Persistent Delusional Symptoms and Disorders

Persistent delusional symptoms and disorders. Topics covered:

  • Introduction
    • The paranoid spectrum
    • Problems of nomenclature
  • A brief historical review of the delusional disorders
  • Delusions: clinical aspects
  • Particular features of delusions in delusional disorder
  • Delusional disorders: clinical features
    • Official diagnostic criteria
    • General aetiological considerations in delusional disorders
  • Delusional disorder: general features and introduction to the subtypes
    • The subtypes of delusional disorder
  • Delusional disorder: persecutory and litigious subtypes
    • Clinical features
    • Litigious variety of the persecutory subtype (querulous paranoia)
    • Diagnosis of the persecutory subtype
    • Differential diagnosis
    • Epidemiology
    • Aetiology
    • Course and prognosis
    • Forensic complications
    • Treatment of the persecutory subtype
  • Delusional disorder: somatic subtype (monosymptomatic hypochondriacal psychosis)
  • Clinical features
  • Differential diagnosis of delusional disorder: somatic subtype
  • Epidemiology
  • Aetiology
  • Course and prognosis
  • Treatment of the somatic subtype
  • Delusional disorder: jealousy subtype
    • The phenomenon of jealousy
    • When does jealousy become pathological?
    • The impact of pathological jealousy
    • Clinical features
    • Epidemiology
    • Aetiology
    • Course and prognosis
    • Differential diagnosis
    • Forensic complications
    • Treatment
  • Delusional disorder: erotomanic subtype
    • Clinical features
    • Diagnosis and differential diagnosis
    • Epidemiology
    • Aetiology
    • Course and prognosis
    • Forensic complications
    • Treatment
  • Delusional disorder: grandiose subtype
  • Clinical features
  • Differential diagnosis
  • Epidemiology
  • Aetiology
  • Course and prognosis
  • Treatment
  • Delusional disorder: mixed and unspecified subtypes
  • Other disorders with persistent delusions
    • Delusional misidentification syndromes (DMIS)
    • Paraphrenia
    • Late paraphrenia
  • Folie à deux: a phenomenon which may accompany illnesses with delusions
    • Subtypes
    • Classification
    • Diagnosis
    • Epidemiology
    • Aetiology
    • Course and prognosis
    • Treatment
  • Treatment of delusional disorder
    • General aspects of the treatment of delusions
    • Treatment approach
    • Practical aspects of treatment
    • Recognition and treatment of postpsychotic depression
  • Conclusions
  • Further reading 
  • References


Delusional disorder (DSM-IV 297.1 and ICD-10 F22) (1,2) is a psychotic illness with some superficial resemblances to schizophrenia from which, however, it is quite distinct. It presents with a stable and well-defined delusional system which is typically ‘encapsulated' from a personality which retains many normal aspects, unlike the situation in schizophrenia where there is widespread personality disorganization in addition to the psychotic features. Nevertheless, although many normal aspects of the personality are preserved, the individual's way of life becomes progressively overwhelmed by the intensity and intrusiveness of the delusional beliefs. Hallucinations may be present but are not usually prominent. This is a chronic disorder, probably lifelong in most instances, which retains an unjustified reputation for being untreatable. Because of the nature of their delusions, many patients are unwilling to accept that they have a mental disorder or that they require psychiatric treatment but, if they can be persuaded to co-operate and accept appropriate medication, the condition can be shown to respond to treatment in a remarkably high proportion of cases.

Delusional disorder is the name now applied to the illness previously known as ‘paranoia', and the terms are virtually synonymous. Paranoia and its related disorders were regarded as an important group of psychiatric illnesses until the early part of the twentieth century. Then, because of changing diagnostic and classificatory approaches, especially the tendency in some quarters to overdiagnose schizophrenia, the diagnosis of paranoia and a companion illness, paraphrenia, practically stopped and they all but disappeared from standard classificatory systems. In 1987, paranoia was again officially recognized by DSM-IIIR (3) but was renamed delusional (paranoid) disorder—since simplified to delusional disorder. It is currently the only officially acknowledged member of the old group of paranoid illnesses appearing in DSM-IV and ICD-10.

Although the diagnosis of paranoia almost ceased for many years, the illness and its sufferers did not disappear. When the phenomena of the disorder came to attention, one of two things tended to happen. Either the patient was labelled as schizophrenic or else a specific feature of the delusional symptomatology was seized upon and spurious syndromes were described. Therefore, as will be noted in the brief historical review below, we have a multiplicity of apparently disparate diagnoses such as de Clérambault's syndrome (delusional erotomania), the Othello syndrome (delusional jealousy), querulant paranoia (a form of persecutory delusional disorder), monosymptomatic hypochondriacal psychosis (delusional disorder with somatic preoccupations), and many others. The result has been an extraordinarily scattered literature with cases recorded in a variety of medical and non-medical sources, but very few in psychiatric publications until recently. It is only since the publication of DSM-IIIR that a serious attempt has begun to resolve a profoundly confusing situation and once again to diagnose paranoia/delusional disorder on the basis of its own intrinsic features. Later in this section, some of the problems still bedevilling nomenclature will be discussed.

Jaspers, in discussing paranoia, said: ‘Why are the paranoics as defined by Kraepelin so rare, yet when they do occur they are so typical?' This is one of the outstanding paradoxes concerning delusional disorder. There are striking similarities from case to case and the illness has features which clearly distinguish it from other psychoses, yet even now diagnostic practices often lead to its being confused with illnesses such as schizophrenia.

Many psychiatric illnesses are associated with persistent delusions, but DSM-IV and ICD-10 provide criteria to differentiate delusional disorder as an illness in its own right and these are now widely accepted. This section adopts this official approach but with two caveats. The first is that the descriptions are bald and not very helpful to the clinician who has not actually seen cases of the disorder. The second is that the category of delusional disorder (persistent delusional disorders in ICD-10) may well be over-restrictive at present. However, it should be noted that some well-respected authorities (4,5) take a somewhat different approach, regarding ‘delusional disorders' as all psychiatric illnesses with delusions and then subcategorizing according to the underlying syndrome, which might be severe mood disorder, schizophrenia, delusional disorder (as in DSM-IV and ICD-10), etc. Therefore the reader must be aware of each author's particular criteria for the diagnosis.

Emil Kraepelin (1856–1926) clearly described paranoia and he included it in a continuum of illnesses with delusional features, which also subsumed paraphrenia and paranoid schizophrenia. This so-called paranoid spectrum will be described later. Paranoid schizophrenia continues to be a widely used diagnosis, but nowadays it officially belongs to the group of schizophrenias rather than with the delusional disorders. Paraphrenia is not officially acknowledged in DSM-IV or ICD-10, but cases fitting its traditional description are not uncommonly seen in practice. A short account of its putative features is provided later in this chapter and an argument advanced for its reacceptance as a discrete disorder within a paranoid spectrum. A somewhat contentious diagnosis—late-onset paraphrenia—has relevance to the contention that paraphrenia does exist, but as a concept it is not widely used outside the United Kingdom; its features will be considered when describing paraphrenia itself.

At present, ‘delusional disorder' is both an illness category and essentially the only syndrome contained within that category. In recent years, another diagnosis—delusional misidentification syndrome ( DMIS)—has come into increasing prominence. This group of disorders was first specifically reported in 1923 by Capgras and Reboul-Lachaux(6) who described the phenomenon of delusional conviction that someone in the patient's environment has been replaced by an almost exact double. For a long time the ‘Capgras syndrome' led a rather marginal existence in the literature, sustained mainly by occasional anecdotal descriptions and spurious psychodynamic explanations, but in the past decade there have been considerably more case reports, descriptions have become more objective, and clinical subtypes have been distinguished. Most importantly, sound psychological and neuropathological work has been carried out and there has been an increasing ability to demonstrate scientifically the presence of significant cerebral pathologies in a high proportion of sufferers.

DMIS is not currently recognized by DSM-IV and ICD-10, but it has a number of clinical features similar to those of delusional disorder and there is no doubt that it warrants official acknowledgement and, it is suggested, inclusion in an expanded category of delusional disorders.

Finally, there is an important phenomenon which is found in association with all illnesses with delusions, but is especially prominent in delusional disorder. This is named ‘shared psychotic disorder' in DSM-IV and ‘induced delusional disorder' in ICD-10, but is often still referred to by its long-established name folie à deux. Here, the primary patient has a bona fide delusional disorder and a secondary patient comes to accept the abnormal beliefs as true. The secondary patient is usually a highly impressionable individual living in prolonged close contact with the other; he or she is not truly deluded, but retains the beliefs tenaciously as long as the intimate relationship is maintained. A less common variety is when two individuals each have genuine delusional disorders and, through close proximity, come to share identical abnormal beliefs. Folie à deux is not uncommon and, as will be explained later, there are very practical reasons why the clinician should be aware of its possible presence and the ways in which it may influence management of the case.

The paranoid spectrum (7)

Since Kraepelin's time, many psychiatrists have believed that paranoia/delusional disorder and paranoid schizophrenia are opposite ends of a continuum of psychotic disorders with delusions as a prominent feature. Therefore a simplified schema of the spectrum is

delusional disorder—paraphrenia—paranoid schizophrenia.

Somewhat anecdotally, the literature suggests that approximately 10 per cent of individuals with delusional disorder or paraphrenia will ‘shift to the right' at some stage and deteriorate to schizophrenia. (The proportion may seem higher if the original diagnoses are less than rigorous and if cases of early schizophrenia are included). Otherwise, it seems that the majority of cases of delusional disorder and paraphrenia remain diagnostically stable over a prolonged period.

Several reports have indicated that, as one moves to the left on the spectrum, a family history of schizophrenia becomes progressively less common. The risk for schizophrenia in the close family of a case of delusional disorder appears to be much the same as in the general public.

Although paranoid schizophrenia is invariably grouped with other schizophrenia subtypes, there is still justification for Kraepelin's original concept of its belonging with the delusional disorders. A family history of schizophrenia is approximately half as common in paranoid schizophrenia as in other schizophrenias, and profound disintegration of personality is much less marked. Paraphrenia shares many features with paranoid schizophrenia, but there is even less personality deterioration and the retention of affective warmth and of the capacity for good rapport in paraphrenia make it strikingly different from the emotional coldness and isolativeness of the latter. However, its delusions lack the cohesiveness and encapsulated quality of those in delusional disorder.

When approaching cases in this general area, the clinician may find it helpful to bear in mind the concept of the paranoid spectrum. This, plus a knowledge of the features of its constituent disorders, will make it easier to distinguish delusional disorder from superficially similar conditions. The precise diagnostician will also appreciate its help in recognizing the differences between paraphrenia, paranoid schizophrenia, and other schizophrenias, a process of some importance in pursuing management and deciding on prognosis.

Problems of nomenclature

Although English-speaking psychiatrists (and most members of the general public) customarily use the word ‘paranoid' to mean ‘persecutory', strictly speaking its meaning is ‘delusional'. (8) In many writings on ‘paranoia' and ‘paranoid' disorders, authors do not make it clear whether delusions are present or not in their cases.

Paranoia used to be an acceptable name for an illness characterized by a well-organized delusional system in a relatively undeteriorated personality, with delusional contents especially of persecution, hypochondriasis, jealousy, erotomania, and grandiosity. Unfortunately, with the passage of time, its usage became so loose that it ceased to have a useful meaning in clinical practice. The term ‘paranoia' should now be regarded as historical and be seen as more or less synonymous with delusional disorder.

The term ‘paranoid' is still used in the official diagnoses of paranoid schizophrenia and of paranoid personality disorder. The first usage is acceptable enough because the illness is a psychosis and has delusions as a prominent feature, but it is quite illogical in describing a personality disorder which, by definition, does not have delusions. It seems unlikely that the personality disorder will be renamed, and so the reader is warned of the pitfalls in our psychiatric terminology and is again cautioned to read the literature with great care.

A brief historical review of the delusional disorders

Although the form of delusional disorder is remarkably characteristic, the delusional contents and the ways in which cases come to attention are extremely varied. This has led to an extraordinarily complex history. The core description, that of paranoia, gradually crystallized in the second half of the nineteenth century and was definitively delineated by Kraepelin, (9) who recognized subtypes with delusional contents of grandiosity, persecution, erotomania, and jealousy, and also allowed for the possibility of a hypochondriacal content. He clearly differentiated paranoia from dementia praecox (later renamed schizophrenia by Bleuler (10)). At first, Kraepelin accepted that auditory hallucinations could occur in paranoia but later (we believe mistakenly) excluded all forms of hallucination from the description. Except that non-prominent hallucinations are now acceptable, Kraepelin's century-old definition of paranoia still largely serves as that of present-day delusional disorder.

Subsequently, Kraepelin (11) introduced the concept of paraphrenia, an illness similar to paranoid schizophrenia but with significantly better preservation of affect and of personality. As already mentioned, he regarded paranoia, paraphrenia, and paranoid schizophrenia as a relatively discrete group of illnesses, later referred to as the paranoid spectrum.

After Bleuler (1857–1939) coined the term ‘schizophrenia', he and other authorities gradually widened the definition of this illness, so that first paraphrenia and subsequently most cases of paranoia were absorbed into the overblown category. This process was accentuated by the finding that a proportion of cases of paranoia and paraphrenia (although certainly not all) eventually deteriorated to schizophrenia. (12,13) By the middle of the twentieth century, paraphrenia in the Kraepelinian sense was rarely diagnosed and paranoia had come to be regarded as a curiosity; in fact, many psychiatrists simply denied its existence.

Despite this, various workers continued to contribute to speculation on the nature of delusions and of paranoia. Karl Jaspers (1883–1969) wrote outstandingly on the phenomenology and psychopathology of delusions, (14) and his work continues to influence the views of many psychiatrists. Kretschmer (1888–1964) proposed that paranoid symptoms tended to occur in abnormally sensitive individuals who suffered from lifelong conflict between feelings of inadequacy and of unrequited self-importance and who, after undergoing some ‘key experience', were precipitated into a delusional psychosis ( sensitiver Beziehungswahn). (15) Kretschmer's observations tended to emphasize (perhaps overemphasize) the importance of pre-existing personality disorder in paranoid illness. Sigmund Freud (1856–1939) wrote extensively on paranoia, (16,17) proposing ‘latent' homosexuality as the underlying psychopathology, a view no longer widely accepted.

Although these and many other speculations have contributed much to the descriptive phenomenology of delusions, we are left knowing a good deal about delusional contents and little or nothing about the mechanisms underlying delusions and their associated illnesses. (18,19) In particular, we have little idea as to how the unique features of the delusional disorders come about. Most unfortunately, much of the extensive theoretical literature on paranoia appeared at a time when most psychoses, and certainly paranoia, had no effective treatments, and virtually all the authors emphasized the condition's untreatability. This pessimistic view continues over into many modern writings and is quite wrong.

From the 1970s onwards, interest in paranoia began to reappear (20,21) and a more optimistic view of treatment emerged. (22) In 1987, DSM-IIIR returned to a description of the illness which was essentially that of Kraepelin, except that non-prominent hallucinations were allowable, and renamed it delusional (paranoid) disorder, now simplified to delusional disorder in DSM-IV and ICD-10. Paraphrenia has not so far been reaccepted and this diagnosis remains in official limbo.

Despite the vagaries of paranoia during much of the twentieth century, several of its subtypes developed quasi-independent existences. Unfortunately, their recognition depended almost entirely on the content of the abnormal beliefs and the form of the underlying illness was often poorly perceived; this has led to much confusion between cases of paranoia and cases of quite different provenance which happen to share apparently similar beliefs, and the distinction between delusions and overvalued ideas has often been blurred. Nowadays we recognize much more clearly that the ‘primary' erotomania of de Clérambault is a subtype of delusional disorder, as are the monodelusional types of pathological jealousy (the Othello syndrome) and hypochondriasis (monosymptomatic hypochondriacal psychosis). In addition, certain cases of persecutory delusional illness and irrational litigiousness (litigious paranoia) prove to be cases of delusional disorder. Since each of these subtypes has developed a literature separate from the others and from the mainstream literature on delusional disorder, tracing the history of the overall concept is a daunting task.

At present the clinical description of delusional disorder is well established, but adequate case series are rare and scientific investigations are in their infancy. The separateness of this illness from schizophrenia is beyond doubt, but its relationship to other disorders within the paranoid spectrum still has to be established. Delusional disorder is no longer regarded as rare, but psychiatrists too often remain ignorant of it and are unaware that many cases are being dealt with by other professionals whose literatures describe typical cases which, however, are often not recognized for what they are.

Delusions: clinical aspects

A delusion may be defined very loosely as a mistaken idea which is held unshakeably by the patient and which cannot be corrected. As will be seen, this is not a satisfactory definition, although it may be a useful starting-point for clinical recognition of a delusional process. This brief exposition is concerned to facilitate clinical recognition rather than to dwell on psychopathological theories which are dealt with in detail elsewhere on this site. 

It is a widely held view that delusions are qualitatively different from normal ideas or beliefs and have an all-or-nothing quality. The DSM-IV definition initially seems to accept this viewpoint, stating that a delusion is ‘A false belief based on an incorrect inference about external reality that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the person's culture or subculture.' But the definition then goes on to say that it is often difficult to distinguish between a delusion and an overvalued idea (in which there is an unreasonable belief or idea but not held with such pathological certitude as in a delusion), and that ‘Delusional conviction occurs on a continuum' from normal to abnormal. These two statements markedly lessen the initial description of the absolute nature of the delusional wrongness.

The definition of delusion by Mullen (23) based on the earlier description by Jaspers is widely quoted and its implications are largely accepted by DSM-IV and ICD-10. He characterizes delusions as follows.

  1. They are held with absolute conviction
  2. The individual experiences the delusional belief as self-evident and regards it as of great personal significance.
  3. The delusion cannot be changed by an appeal to reason or by contrary experience.
  4. The content of delusions is unlikely and often fantastic.
  5. The false belief is not shared by others from a similar socio-economic group.

Clinicians widely employ the terminology on delusions introduced by Jaspers, for example when they use terms such as ‘primary' and ‘secondary' delusions, ‘delusional mood' (Wahnstimmung), and ‘delusional memory'. These concepts are of some descriptive and possibly heuristic value, but they do not prove particularly helpful in distinguishing delusions from overvalued ideas in individual cases, nor in deciding whether a particular delusional phenomenon is specific to a given mental disorder.

In a sense, all delusions are secondary in that they are the product of a pathological process in the brain which, in most cases, we can only guess at. It is sometimes useful to differentiate clinically between the ‘primary' or ‘autochthonous' delusion, which appears fully fledged and relatively suddenly, and the ‘secondary' delusion, which is a further development within the delusional system and may sometimes seem to be the individual's way of rationalizing his delusional beliefs although, of course, the rationalization must necessarily be filtered through a mind already thought-disordered and affected by delusions. For example, the initial belief may be that the police are watching him night and day; the secondary delusion ‘explains' that this is because he has secret information about aliens which the authorities do not wish divulged. The better organized the delusions, the more convincing are the ‘explanations', even to outsiders.

Not all primary delusions arise suddenly and, in fact, it must be presumed that in most cases the suddenness is more apparent than real. Almost certainly, unless the delusion is the result of an acute brain dysfunction such as may follow a head injury or delirium, there is a lead-up process which may be accompanied by the above-mentioned Wahnstimmung, a mood state compounded of anxiety, perplexity, and a sense of impending crisis. When the delusion crystallizes, the delusional mood often disappears and is replaced by a sense of revelation and of certainty. It seems likely that this phenomenon occurs in a proportion of delusional disorder patients and it often happens that, at the moment of revelation, some coincidental but irrelevant circumstance is picked upon to explain the appearance of the new belief. For example, a media event, a thunderstorm, a chance telephone call, etc., may thereafter be, in the patient's mind, the ‘cause'.

While psychiatrists regard delusions as one of the most characteristic elements of all the psychotic illnesses and a sine qua non in the diagnosis of delusional disorder, clear-cut description and delineation have proved elusive despite many years of study and experiment, especially by clinical psychologists. (24) In fact, Garety and Hemsley (18) point out that, even now, none of the characteristics of delusion which we traditionally accept completely stand up to scientific scrutiny. For example, it turns out that delusions are not necessarily rigidly fixed, but may fluctuate in the intensity with which they are held. They are not totally incorrigible and it has been shown that some at least are modifiable by psychological approaches, and they are certainly not invariably absolute yes–no entities. A delusion need not always be a blind belief and some individuals freely reflect upon the abnormal ideas, even showing some insight at times. In particular, nowadays the so-called bizarreness of a delusion has been shown to have little or no distinguishing value. (25)

Much of the classical work on delusions was done in pretreatment times when the chronic condition was readily available for study in institutions. In the present era our aim is to diagnose psychotic disorders as early as possible, sometimes even before frank delusions are evident, and to begin treatment at once. Neuroleptics rapidly interfere with many psychopathological processes; they certainly suppress delusions, although not necessarily permanently. Of course this makes ongoing experimental observations of delusions, especially acute delusions, all but impossible in clinical circumstances. Psychiatrists find themselves in the paradoxical situation of diagnosing illness because of the presence of delusions whose scientific validity is largely unsubstantiated, and then causing them to disappear before they can be verified properly. Nevertheless, until we have more objective means of making diagnoses it remains essential that, as far as we can, we recognize delusions when they occur and separate them from other abnormal psychopathological appearances.

How can a clinician deal with this? Firstly it seems inescapable that he or she be both experienced and insightful. Given these qualities, it often does seem possible to have an informed sense as to whether a belief is true or false and, if the latter, whether it is being held with delusional intensity. A key element in the decision is a comparison between the patient's current beliefs and those he habitually held, and here a corroborative account from an informed outside source is usually necessary.

The observer's educated suspicion that a delusion is present is the starting point, but it is evident that suspicion has to be aroused by the context of the apparently delusional idea because, no matter how isolated it appears to be, it will usually occur in the setting of a mental disorder whose other features may be typical of a specific psychiatric diagnosis. Illogically, instead of recognizing the delusion and using it to make a specific diagnosis, we often recognize that we are dealing with a probable psychosis and thereafter judge all the patient's utterances in light of that. While he may indeed be experiencing delusions, it is essential that we do not automatically assume that anything the psychotic individual says is of a delusional nature. The following brief case study demonstrates the danger of doing this.

Case Study:

An elderly man was admitted to hospital, possibly with severe depressive disorder. During history-taking he said that the people upstairs watched him through his ceiling and stole things from him. This was taken as evidence of delusional thinking until a social worker visited his home, which was in a decrepit building. It turned out that there actually was a hole in his ceiling, and that his upstairs neighbours did watch him and did steal from him by reaching down with a walking-stick and lifting belongings from his mantelpiece.

We must accept that we cannot be absolute in our recognition of a delusion. In addition to the illness context we base our estimate on a series of nuances, no one of which is pathognomonic but an accumulation of which becomes increasingly convincing. The abnormalities to be sought are as follows.

  1. An idea or belief is expressed with unusual persistence or force.
  2. As far as we can tell, the idea is not typical of the individual's previously prevailing thinking and is not shared by his or her social community.
  3. The idea appears to exert an undue influence on the person's life and consequently the way of life is altered to an extraordinary degree.
  4. Despite the significance to the patient of the belief, he or she often displays secretiveness or resentment when questioned about it.
  5. The individual tends to be humourless and oversensitive about the belief.
  6. There is a quality of ‘centrality'; no matter how strange the belief or its consequences, the patient rarely questions that incredible things are happening to him or her. For example, why should a perfectly ordinary harmless person be singled out for constant surveillance by the security agencies? But this is simply accepted.
  7. Attempts to contradict the belief are likely to arouse an inappropriately strong emotional reaction, often with irritability and hostility and with a superciliousness that may be a form of grandiosity.
  8. On reflection the belief appears unlikely to the observer, but at the time of history-taking the force of the patient's expression of it may temporarily disguise its improbability.
  9. The patient is so emotionally overinvested in the idea that it swamps other elements in the psyche, and many everyday activities are neglected.
  10. If the delusion is acted out, uncharacteristic behaviours, sometimes involving violence, will occur which may be partly understood in terms of the abnormal belief.
  11. Others who know the patient well will usually observe that his or her thinking and behaviour are alien, unless folie à deux is present when, paradoxically, the other person's denials of abnormality may actually tend to confirm the presence of delusion.
  12. An odd feature of delusions is that, no matter how strongly they are held, when the patient is given the opportunity to obtain ‘proof' he or she persistently evades taking the appropriate action. 13.
  13. One must always look for the features which frequently accompany delusions, especially suspiciousness, hauteur, grandiosity, evasiveness, and eccentric or threatening behaviour, as well as evidence of thought disorder, mood change, and hallucinations.

Particular features of delusions in delusional disorder

In addition to any of the above, in delusional disorder we find several other elements which are of importance in leading to the diagnosis.

  1. The delusional system is stable and is expressed or defended with intense affect and with highly rehearsed arguments. The form of the logic used by the patient is very consistent but the propositions are based on false premises. Since the individual is so focused on his beliefs he often succeeds in making the enquirer feel inept with his or her self-assurance.
  2. The delusional system is markedly ‘encapsulated', so that the beliefs therein and their accompanying symptoms are to a considerable extent separate from the rest of the personality which retains a good deal of normal function. However, the compelling force of the delusions often overshadows these normal aspects and this is increasingly so with advancing chronicity of the illness, when the tendency to express and act out the delusions may well increase.
  3. When the individual is preoccupied with the delusional system there is strong emotional and physiological arousal, but when he or she is engaged on neutral topics, the arousal abates and an ordinary conversation can take place. Switching between normal and abnormal ‘modes', sometimes very rapidly, is virtually pathognomonic of delusional disorder.
  4. Because of the encapsulation of the delusions and the normal– abnormal switch just described, the patient may have phases of relative normality interspersed with psychotic periods. The switch can occur spontaneously or as a result of external provocation; the two are difficult to disentangle since the hypervigilant individual may perceive provocation in almost anything. Since it is a chronic illness the symptoms never remit, but if they are temporarily in the background the patient may converse and function almost normally and may have sufficient quasi-insight to keep the delusions concealed. Total denial of mental abnormality and resistance to psychiatric referral are almost universal in cases of delusional disorder and lead to severe underestimation of the illness's frequency.
  5. As a result of the features just described, many delusional disorder patients can continue to exist in society, sometimes with very abnormal but harmless beliefs but in other instances with highly malignant delusions which they may or may not act out.
  6. As will be repeatedly emphasized, delusional disorder must be diagnosed on the form of the illness and the content of the delusion is not used to make the primary diagnosis. On the other hand, the particular content is employed to categorize into subgroups, as will shortly be described.

Delusional disorders: clinical features

Official diagnostic criteria

The DSM-IV and ICD-10 criteria are shown in Table 1 and Table 2 respectively.

As will be seen, the DSM-IV and ICD-10 descriptions are very similar in overall outline but with a number of rather striking minor differences. The following specific features should be noted.

  1. DSM-IV uses the term ‘non-bizarre' delusions; this criterion has been shown to have little or no validity. (25)
  2. DSM-IV allows the presence of tactile and olfactory hallucinations, while ICD-10 mentions only auditory hallucinations; in practice most modalities may be represented but the important point is that they are relatively non-prominent and usually parallel the content of the delusion(s).
  3. DSM-IV says that delusions should have been present for 1 month and ICD-10 insists on 3 months. Both are guesses, but ICD-10 is probably right to err on the side of caution and it provides category F22.8 as a temporary niche until the definitive diagnosis emerges.
  4. Both classifications exclude delusional illnesses due to organic brain disorder, medical illnesses, medication effects, or psychoactive substance abuse. In essence this is correct, especially in an illness of acute onset. However, as will be noted later, an apparently typical delusional disorder may arise as a long-term complication of any of these factors.
  5. DSM-IV and ICD-10 agree emphatically that delusional disorder is not schizophrenia and DSM-IV notes that general functioning is not impaired. Both say that mood disturbance may accompany the delusional illness but is not a cause of it.
  6. The list of subtypes according to delusional content is similar in both classifications, although ICD-10 adds self-referential and litigious themes.
  7. Neither classification specifies that the essence of delusional disorder is a highly organized delusional system, largely encapsulated from normal aspects of the personality, although DSM-IV hints at this when it comments that functioning is not markedly impaired and behaviour is not obviously odd or bizarre. Neither comments that the patient can demonstrate alternating ‘normal' and ‘delusional' modes.
  8. The ICD-10 category of ‘other persistent delusional disorders' is vaguely described and is largely a catch-all heading or, as mentioned above, a temporary holding station. However, it could conceivably be used for the time being to subsume the unofficial delusional disorder diagnoses of paraphrenia and delusional misidentification syndrome which will be described later.
  9. Overall, DSM-IV and ICD-10 give rather laconic descriptions of delusional disorder and it will be necessary to flesh them out with relevant clinical details. This will be done immediately after the next section on aetiological considerations.

General aetiological considerations in delusional disorders

It must be stressed that knowledge of aetiology in delusional disorder is scanty and highly speculative, largely because so little modern research has been conducted. What follows is an outline, and certain other factors will be noted when we come to consider the individual subtypes of the illness.

Genetic factors

Changes in definitions of paranoia/delusional disorder over the years and the frequent confusion with schizophrenia make most studies all but impossible to interpret. Conclusions are inferential rather than evidence based. However, it seems well established (26) that delusional disorder and paranoid schizophrenia are less directly inherited than other forms of schizophrenia, and that there is little or no evidence of a genetic link between delusional disorder and schizophrenia. There may be genetic links with certain severe personality disorders, especially of the paranoid and schizoid varieties, but these are difficult to substantiate. There does seem to be an excess of such disorders in relatives and premorbidly in delusional disorder patients themselves. It is suggested that paranoid and schizoid traits are particularly liable to lead to social isolation and aggravation of delusional tendencies. (27,28)

Organic brain factors

Recent evidence from the study of delusional misidentification syndrome (see later) indicates that delusions of a very specific type may arise in association with certain well-defined brain insults. There are strong hints, but much less supportive evidence, to suggest that organic brain factors may also be important in cases of delusional disorder. For example, head injury may lead to the development of marked paranoid symptoms, and there is a long-established association between chronic alcoholism and pathological jealousy. (29) Old age itself may be linked to the onset of symptoms typical of delusional disorder, and early evidence of brain changes, especially in subcortical areas, is starting to appear in studies of various kinds of senile ‘paranoid' illness. (30,31 and 32) Amphetamine (33) and cocaine abuse (34) can induce delusional illness, as can therapeutic drugs, including L-dopa and methyldopa, at times. Delusional illness induced by the brain effects of AIDS infection has been documented in recent years. (35)

Gorman and Cummings (36) have proposed that delusional illnesses of organic origin have underlying features in common, particularly temporal lobe or limbic involvement and an excess of dopamine activity in certain areas of the brain.

If organic factors predominate in a particular case, delusions must be seen as a secondary feature of an organic brain disorder. However, if the organic factors are subtle and of long duration, the clinical appearances may be those of a quite typical delusional disorder which, interestingly, may well respond to neuroleptic treatment as effectively as idiopathic cases. (In fact, ‘idiopathic' may simply denote organicity at a more subtle level.) It is very possible that organic brain factors are much more common than we suspect in delusional disorder, especially in younger males who have previously abused alcohol or drugs or have suffered a head injury in the past, and in older patients (more commonly female) who suffer from effects of an aging brain. (37)

Interplay with mood factors (38)

We have already seen that DSM-IV and ICD-10 agree that mood symptoms may accompany delusional disorder but not cause it. Delusional and mood disorders are separate illnesses with their own natural histories and responses to treatment, yet there is a complex relationship between them, as is also the case with mood disorder and schizophrenia. For example, it is well documented that some cases of apparently typical mood illness, unipolar or bipolar, can progress to delusional disorder or schizophrenia over time. Conversely, cases which appear to be delusional disorder but with an episodic course may prove to be bipolar illness. There are a number of anecdotal reports of delusional disorder responding to antidepressant treatment, and it is more than likely that these represent a failure to recognize the true nature of a mood disorder associated with delusions.

Both depressive disorder and mania may be complicated by delusions. On the other hand, mood symptoms, especially dysphoria with anxiety, are a common complication of delusional disorder, while individuals with the grandiose subtype may show elation which mimics mania but is far more sustained. In recovering delusional disorder, one may see postpsychotic depression of varying degrees of severity and this is described later. Suicide is not unknown in delusional disorder but its frequency is undetermined.

In many delusional disorder patients the illness is profoundly isolating and sets them at odds with the rest of society, which often generates suspiciousness, dejection, anxiety, and agitation. It seems that a vicious circle results whereby the delusion induces distress and physiological overarousal which, in turn, reinforce the strength of the delusion and progressively diminish reality input.

Psychodynamic theories of causation

The psychodynamic literature continues to discuss aspects of ‘paranoia' but often fails to differentiate clearly between trait, symptom, personality disorder, and psychotic illness. Freud postulated that paranoia (by which he probably meant delusional disorder) was the result of regression from the homosexual phase of psychosexual development to a fixation at the primary narcissistic phase. Homosexual feelings unacceptable to the individual are transformed by projection into suspiciousness and rejection—in this theory, an understandable warding-off of supposed homosexual advances. This scenario involving repressed homosexuality is assumed with no convincing proof and there seems to be no established connection between homosexuality and delusional disorder, although cases of delusional disorder in homosexuals are recorded. (39,40)

There are many psychoanalytic references to the central role played by depression in the genesis of paranoia but, as already explained, this does not appear to be true of delusional disorder. (41)

Klein (42) postulated a fixation at the paranoid–schizoid position, said to occur between the sixth and ninth months of life, inducing profound hatred by the infant of the mother, symbolically represented by the maternal breast, and envy of other women, ultimately leading to paranoia. Many other theorists have regarded narcissistic mechanisms as central, with paranoia arising from repeated empathic failures and narcissistic injuries to the developing self. (43) Paranoid delusions have been described as an escape, via projective mechanisms, from shame, guilt, and inadequacy, with persecutory and grandiose beliefs attempting to overcome a prevailing sense of inferiority. A recurring suggestion is of weakness counteracted by paranoid aggressiveness which is projected on to the external object who can then be perceived and blamed as an aggressor. (44)

Much of the psychodynamic literature dwells on the persecutory aspect of paranoia, with only occasional forays into other types of delusional content. Since psychotherapists rarely treat psychotic patients, their experience of delusional phenomena must actually be rare and their knowledge of the features of delusional illness correspondingly scanty. (45) Their theoretical bias is to interpret the origin of paranoia in terms of psychological maldevelopment, ignoring the increasing weight of evidence that faulty brain mechanisms are involved. One must read the psychodynamic literature on this particular topic with an ultracritical approach, since it usually fails to provide adequate illness definitions or clear case reports and generates explanatory theories which are unjustifiably presented as proven facts.

Conclusions regarding aetiology

No systematic research on paranoia took place for more than half a century and modern investigations into delusional disorder are only beginning to appear. Therefore it is premature to propose specific aetiological hypotheses. However, a gathering weight of evidence does suggest a localized and relatively circumscribed brain disorder associated with the possible influence of abnormal neurotransmitter activity, probably involving dopamine overactivity. Whatever the original basis of delusional disorder, it certainly seems that provocative influences such as head injury, alcohol abuse, and ill effects of drugs can evoke the expression of the illness. Hereditary factors and association with inherited personality factors may play a part, but theories of psychological maldevelopment suggest that this is at most a secondary influence. There is an urgent need for the study of extended case series utilizing modern neurophysiological and neuropsychological investigative methods.

Delusional disorder: general features and introduction to the subtypes

We have already outlined the diagnostic criteria for delusional disorder in DSM-IV and ICD-10 and have amplified these with descriptions of many of the clinical phenomena associated with the illness. It has been emphasized that this is a stable and readily recognizable disorder, provided that the clinician is informed of the essential criteria and has dealt with at least several cases to familiarize him- or herself with its very characteristic ‘feel'. With this experience it becomes much more possible to delve under the prominent symptoms related to delusional content and to discern the underlying form of the illness. However, it is the predominant delusional content in an individual case, and the symptoms and behaviours related to this, which decide how a patient will present for assessment. Therefore we shall consider the main subtypes in some detail. It cannot be stressed enough that these are not separate types of illness, but variants on a single psychopathological theme.

All cases of delusional disorder occur in clear consciousness and have a stable and persistent delusional system which is relatively encapsulated. Since much of the personality remains remarkably intact, a considerable degree of social functioning is retained in many cases. The patient experiences a heightened sense of self-reference within the delusional context and ordinary events take on extraordinary significance. He or she clings to the delusion with fervid intensity and spurns any suggestion that a mental illness is present. Outside the delusional system the patient shows quite normal thinking, affect, and behaviour, but there is a marked tendency for gradual pushing to one side of these normal aspects. The retention of such a degree of normality makes the illness totally different from schizophrenia.

Earlier it has been indicated that the DSM-IV criterion of ‘non-bizarreness' is unhelpful. (25) In all cases of delusional disorder the delusions tend to be well structured, coherent, and consistent, and the logic would often be acceptable if it were not that its basic premises are irrational. Many affected individuals can maintain overtly normal activities, at least in public, but increasing pressure of the delusion tends to cause corresponding responses in behaviour; these may be channelled socially, as in hypochondriacally deluded patients who utilize medical resources, albeit excessively, or antisocially, as in the aggression of the jealously deluded individual. Mood abnormalities are common as a response to the effects of the illness.

Hallucinations do occur in some cases and may affect any modality, but they are often difficult to assess and to differentiate from delusional misinterpretations and illusions. Widespread persistent hallucinations in more than one sensory sphere should make one cautious of the diagnosis of delusional disorder.

The illness appears to affect men and women approximately equally, but it is not clear if this is true of all subtypes. Despite older assertions that the illness is restricted to the middle-aged and elderly, the age of onset can actually be from late adolescence to extreme old age, with male patients appearing on average to experience earlier initiation. Some patients behave in an eccentric or fanatical fashion and, as a group, delusional disorder sufferers are excessively likely to be unmarried, divorced, or widowed, probably reflecting restriction of affective responses and some asocial tendencies. Despite this, the condition can be compatible with marriage and continued employment. The premorbid personality is usually described as asocial and there may indeed be an excess of long-standing schizoid and paranoid personality disorders. However, when a patient makes a good recovery there may be little evidence of this, and it is possible that in some cases a ‘personality disorder' is actually the prolonged and insidious prodrome of the illness.

Onset may be gradual or acute. In the latter the patient often identifies a precipitating stressor which is difficult to confirm (e.g. the person who has a delusion of skin infestation may attribute it to a single insect bite many years previously). While most individuals are secretive about their abnormal beliefs or express them by such means as physical complaints or legal processes, a certain number actually utilize them, perhaps within the context of an extreme religious sect or by becoming an excessively insistent agitator on some social issue. Disinhibited and overtly aggressive behaviour seems usually to be more frequent in males, leading to clashes with authority.

In all cases of delusional disorder, no matter what the nature of the delusional theme, the investigator should look for the relatively unique feature of the illness—the patient's ability to move between normal and delusional modes of thinking. In the former there is relatively calm mood, reasonable rapport, and appropriate emotional reactions, whereas in the latter there is overalerting, suspiciousness, and the sense that the person is being remorselessly driven by the delusional beliefs. This situation is difficult for the inexperienced observer to comprehend, since it is inconceivable to most people that someone who can appear perfectly rational at one moment can almost instantaneously change to a possessed irrational being—and then back again just as quickly. In a sense the same patient is both sane and insane, and when in the latter mode may be ultrapersuasive about the acceptability of his or her beliefs. One may imagine the plight of a lawyer faced with a client who has committed some uncharacteristically outrageous act as a result of a delusion who can then discuss his case with apparent insight and logic, and even remorse, but who nevertheless remains totally self-justifying. As a corollary, the client will usually deny the possibility of mental illness and often refuses to co-operate with psychiatric assessment.

Delusional disorder, when it was known as paranoia, often had a bad reputation because patients were regarded as angry, suspicious, accusatory, and potentially violent. Some undoubtedly are, but as we consider the various subtypes nowadays we realize that many sufferers, perhaps the majority, lead lives of internalized despair in increasingly isolated circumstances. Anger and suspiciousness are often secondary, at least in part, to the perceived neglect of their overwhelming concerns. The illness is chronic and self-reinforcing, and it is likely that only a minority of cases are recognized or helped. Psychiatry does not have an impressive record of recognizing or helping this group of patients.

The subtypes of delusional disorder

As previously noted, DSM-IV recognizes five main subtypes of the illness based on the predominant delusional themes: the erotomanic, grandiose, jealous, persecutory and somatic, and mixed and unspecified types. ICD-10 also recognizes these subtypes, and adds litigious and self-referential. Here, the litigious variety is included under the persecutory group and self-referential cases are not given separate status since self-reference is, in a sense, a feature of the illness as a whole and prominent in all cases.

When delusional disorder was resurrected in DSM-IIIR, single delusional themes were emphasized, but the mixed category in DSM-IV accepts the reality that, for example, a hypochondriacal individual can also feel persecuted and an erotomanic patient can be extremely grandiose. Also, we shall find that there are considerable individual variations within the overall themes, so that in the somatic subtype there are cases involving different body systems. Yet the range of themes does not appear to be all that wide and we have no explanation for this relative restriction in their number. The ‘unspecified' category in DSM-IV allows us to accommodate any case whose delusional theme is unusual and to be open to the discovery of other major themes in the future.

In presenting the subtypes, relatively more attention will be given to the somatic form. This should not be taken as an indication that this is the most common variant; rather, it happens to be the one which has been best documented in the recent psychiatric literature. Other types of delusional presentation are much more often described in non-psychiatric and non-medical sources, where the fundamental nature of the illness may be overlooked, and so we are only beginning to correlate such descriptions with modern findings on delusional disorder.

Delusional disorder: persecutory and litigious subtypes

In most people's minds the persecutory type of delusional disorder is the archetype of ‘paranoia' and it is usually assumed that it is the most common variety. Therefore it is surprising to find that the literature, while full of speculation, is very lacking in good descriptions of the phenomenology of the illness and, apart from psychoanalytic theory, says relatively little about persecutory delusions themselves.

Clinical features

By definition the illness is a chronic psychotic disorder with a well-systematized delusional system and with relative sparing of the surrounding personality. The persecutory threats may be perceived simply as coming from ‘them', but can range from this to descriptions of the most elaborate plots involving a variety of known and unknown adversaries. The beliefs are extremely stable and usually increase in elaboration with the passage of time. There is heightened awareness and misinterpretation of neutral environmental cues and, not unnaturally suspiciousness, extreme anxiety, and irritability are present. Elements of grandiosity are not uncommon, with the individual accepting that he is the centre of focused and malignant attention that would be inexplicable to the normal person. As the illness progresses there is a tendency to involve an increasing number of people in the persecutory system, not uncommonly relatives, physicians, law-enforcement agencies, aspects of government, and others.

As with other subtypes of delusional disorder, many individuals are able to conceal their increasingly insistent delusions at least for some time, but because of fear of harm they are likely to isolate themselves more and more. If they live alone they may come to be regarded as eccentrics, but if they remain in contact with society the suspicion and anger must eventually become evident, so that interactions with family, social agencies, or the authorities become increasingly confrontational. (46) Despite the reputation of ‘paranoia' for violence, only a small proportion of these individuals resort to assault, but in those who do the danger may be profound as the individual is without reservation in his beliefs and will act as though genuinely under severe threat. Disinhibition may at times be provoked by alcohol or drug use, which makes such situations even more volatile.

Even in a long-standing illness, islands of normal functioning remain; despite this there is little or no insight and the patient resists any psychological explanation for his beliefs. He usually refuses to see a psychiatrist voluntarily; many patients of this kind are encountered in a forensic setting only after an outburst of unacceptable behaviour and are minimally co-operative.

Case Study: Persecutory subtype.

A single man of 35 was convinced that he had been infected with AIDS by an antagonistic racial minority group. For several years he moved from place to place and from doctor to doctor trying to obtain confirmation of his diagnosis and appropriate treatment. His serology was negative and he appeared physically well, but he refused to accept this and became increasingly frustrated with the medical profession. He sent threatening letters to his family physician, and then one day walked into the latter's office and severely beat him. When charged he said that he was perfectly justified and that this was a deliberate reprimand to physicians in general for their incompetence. He felt sorry for having injured a particular individual, but he had no alternative and would do it again if he was not properly diagnosed. This man was intelligent and well educated, and had no evidence of psychiatric disorder apart from his single, absolutely fixed, delusional system. 

Litigious variety of the persecutory subtype (querulous paranoia) (47,48)

In some individuals with delusional disorder there is a profound and persistent sense of having been wronged in some way, and these people endlessly and repetitively seek redress, sometimes personally but often through the legal system. In a proportion of cases there may initially have been a genuine grievance and there may also have been unsatisfactory recompense, but the subsequent pursuit of ‘justice' becomes never-ending and also becomes self-reinforcing because no satisfactory resolution is possible.

This group may not be large but it generates considerable media publicity. Reports of cases naturally tend to be in the literature of the legal profession, the law-enforcement agencies, and, to some extent, forensic psychiatry, but rarely from general psychiatry. Because the individual appears relatively high functioning apart from his delusional beliefs, the complaintive behaviour may be regarded as mere eccentricity for a long time. As in many cases of delusional disorder, the immediate complaint and behaviour may seem coherent and not unreasonable but over time their ongoing, never-ending, and extraordinarily demanding quality begin to raise the suspicion of severe underlying psychopathology. Even then, unless the person begins to be perceived as a threat, little may be done and severe harassment of officialdom and the legal system may be accepted for surprisingly long periods. In some national communities (e.g. Germany and the Scandinavian countries) there are legal provisions to stop ‘barratry' or unreasonable use of the law by declaring an individual a querulous litigant.

Goldstein (49) has described three typical ways in which ‘litigious paranoia' presents. The first is the ‘hypercompetent defendant' who knows and uses the letter of the law up to and beyond its limits but pays no heed to its spirit. The second is the ‘paranoid party in a divorce proceeding' who is often consumed with jealousy and pursues vendettas against the ex-spouse, the lawyers on both sides, and even the judge. The third is the ‘paranoid complaining witness' who endlessly initiates litigation despite repeated adverse judgments. All such individuals pursue their grievances in a driven manner, see conspiracy in every corner, and are often quite unscrupulous in their single-mindedness, blatantly bending facts to fit with their beliefs. Since they hold the delusional belief with total conviction, they can accept no counterargument or contrary facts. In the past, persistent litigation was virtually a preserve of the rich, but many modern societies provide a variety of avenues for complaintiveness and will even support complaint procedures, and so abnormally litigious behaviour appears to be on the increase. (50)

Case Study: Litigious delusional disorder

A man in his early forties who is barely literate is well known to local police, the legal system, and the psychiatric profession. He is unmarried and lives alone in squalor. Despite his lack of education, he has developed a remarkable knowledge of the letter of the law. He has insisted for years that neighbours persecute him and he harries them with a noisy radio, by shouting at their house, and occasionally threatening assault. He has repeatedly been cautioned and arrested, but shows a remarkable ability to involve legal aid, the social services, a variety of voluntary agencies, and even the local news media. He is essentially harmless but is a profound public nuisance, and attempts to restrain and incarcerate him always fail in the end. He has never co-operated with any treatment, but several psychiatric examinations have declared him to suffer from delusional disorder of the persecutory/litigious type.

Diagnosis of the persecutory subtype

All the features of a delusional disorder which have been previously described are present. In this subtype, wariness, irritability, suspiciousness, and threatening behaviour are especially prominent, and both impulsive and planned violence may occur. Gaining confidence is extremely difficult, but if this succeeds, the more normal aspects of the individual's personality may become apparent and one may also perceive how chronically afraid and overalerted he or she is.

Differential diagnosis

The illness must be distinguished especially from the following:

  • paranoid schizophrenia
  • paranoid and antisocial personality disorders
  • substance-related disorders
  • organic brain disorders, including early dementia and some epileptic disorders
  • obsessive–compulsive disorder.


Virtually nothing is known of the frequency and distribution of persecutory delusional disorder. As with other subtypes it occurs in both sexes, but male cases are probably over-reported because of a readier tendency to violence and antisocial acts. The literature is biased by the reporting of the most overt cases, often in the news media or in legal situations. (51) It is open to speculation how many cases avoid diagnosis; as noted, relatively few come to the detailed attention of psychiatrists other than forensic psychiatrists.


Hypotheses are of the vaguest. There may be an excess of premorbid personality disorder, especially of paranoid and schizoid types. There do not appear to be close genetic links with schizophrenia or major mood disorder. The delusional system can appear suddenly or insidiously and often for no obvious reason, although previous alcohol and other substance abuse and a prior history of head injury may be significant. The psychoanalytic view of ‘paranoia' is largely based on the persecutory subtype, but the provenance of cases in that literature is usually vague and speculation far outweighs verifiable fact.

Course and prognosis

Delusional disorder is a very chronic disorder, and it is presumed that cases of the persecutory subtype are as likely as others to be lifelong and to show increasing psychopathology with the passage of time. In a proportion of cases there is always a risk of antisocial behaviour and violence. Since co-operation with treatment is usually minimal, the overall figures for prognosis must be bad, but we have no reliable data to confirm this.

Forensic complications (52,53)

If someone with a generalized psychotic disorder like schizophrenia becomes sufficiently disorganized, functioning in the community becomes impossible. In contrast, many patients with delusional disorder retain a sufficient grasp of reality to continue existing in society, sometimes indefinitely. However, this does not imply that their illness is quiescent. Intellectual ability, capacity for reasoning and the form of thought remain relatively intact, but the delusional process worsens. They retain the ability to brood on their beliefs so that normal thought processes and delusions interweave, as do normal and abnormal behaviours. Anger may express itself explosively, but some individuals may carry out violent actions in a very calculated way, believing that a just vengeance is being exacted. Afterwards there may be real regret and a clear awareness of a wrong against society, but nevertheless the actions are seen as justifiable and necessary.

In 1843 the English legal system devised the McNaghten Rules following the trial of McNaghten, a deluded assassin, and these attempted to define the relationship of delusion to crime. Subsequently they were found to be inadequate, since they dwelt on cognitive misapprehension and largely ignored the rôles of emotion, volition, and the capacity for behavioural control. Nowadays the principal issue in cases of delusionally motivated crime is whether or not the accused appreciated the rightfulness or wrongfulness of his action at the time. In delusional disorder the patient is usually aware that by societal standards his deed is legally and morally wrong, but that awareness resides within the normal non-delusional aspect of his mental functioning. Within the confines of the delusional system, the person unswervingly believes that it was necessary to behave as he did.

In such cases, the judge and jury are placed in a quandary, made worse by the individual's frequent arrogance (which is at least partly grandiosity), self-justification, and ambivalent expression of regret. The ability to acknowledge the wrongness of one's act in general terms and even show remorse for it, while also asserting that it was necessary to carry it out, may well be regarded as indicating wilfulness or hypocrisy. Then, paradoxically, culpability may be determined by the content of the delusion, although this usually has minor relevance to the disinhibition of behaviour. Thus, as Goldstein (51) has pointed out, if the person felt threatened because of a delusional belief and reacted, as he genuinely perceived, in self-defence, his degree of blame may be adjudged to be low. But if he were equally deluded and carefully plotted revenge, this might be seen as highly culpable. Such a distinction cannot be defended logically either in the clinical situation or at law.

Delusional disorder defies any definition of insanity in black or white terms; it is both black and white. Because few psychiatrists, even in the forensic field, are familiar with its detailed characteristics, psychiatry has had limited success in educating the legal profession about the subtleties of the illness or the conundrum that delusions can induce such abnormal behaviour in an individual who superficially appears rational and for significant periods of time is effectively sane even though the illness is always present.

Treatment of the persecutory subtype

Treatment is discussed later in this article in the section on overall treatment aspects.

Delusional disorder: somatic subtype (monosymptomatic hypochondriacal psychosis)

Modern society, especially in developed countries, is preoccupied with health concerns. While much of this is positive, there is no doubt that many people worry excessively about health matters and a proportion of these show pathological self-concern. This can shade into hypochondriasis, in which there is a persistent conviction of illness in the absence of objective evidence of its existence, with misinterpretation of bodily sensations as disease and with inability to accept reassurances. In many cases the individual shows some degree of body image disturbance, sometimes of extreme degree. (54,55) Usually we think of hypochondriasis as referring to physical complaints, but nowadays it seems that an increasing number of affected people are also prepared to complain in psychological terms.

Hypochondriasis is common and may be a personality trait, but it can also be an accompaniment to many psychiatric illnesses, both non-delusional and delusional. It is the presenting feature of the somatic subtype of delusional disorder and in different patients we see many varieties of alteration of body image expressed in delusional terms. Certain themes of delusional content tend to predominate and this has meant an unfortunate proliferation of descriptive names scattered across a fragmented literature, leading to many difficulties in conceptualizing the subtype and in separating it from other psychiatric disorders with prominent hypochondriasis.

As with all subtypes of delusional disorder, the clinician must bear in mind the advice already given that, for the diagnosis of delusional disorder, it is the characteristic form of the illness that is of prime importance, not the content of the delusional beliefs. The hypochondriasis in delusional disorder may superficially resemble that of somatoform disorder, psychotic depression, or obsessive–compulsive disorder, but careful examination will reveal very different underlying illnesses.

Clinical features

We shall consider the manifestations of the somatic subtype of delusional disorder under four major theme areas

  1. delusions involving the skin;
  2. delusions of ugliness or misshapenness (dysmorphic delusions);
  3. delusions of body odour or halitosis; 
  4. miscellaneous.
Delusions involving the skin (56,57 and 58)

In the delusion of skin infestation, the patient insists that he has organisms, usually insects, crawling over the surface of the skin and sometimes burrowing into the skin or under the nails. In most instances he cannot see the creatures, but sometimes there may be graphic descriptions. This may represent a visual hallucination but more usually seems to be a vivid ideational projection.

The delusion of parasites burrowing deeply under the skin is often attributed to worm-like parasites, and internal body sensations or the rippling of small superficial muscles are misinterpreted as evidence of their activities. Sometimes the patient believes that the worms have spread throughout the whole body or intermittently migrate from place to place.

In the delusion of discrete foreign bodies under the skin or nails, these bodies are occasionally described as inanimate, but generally the patient says they are seed-like or believes that they are parasite eggs. In some individuals this is associated with an irresistible desire to pick, and multiple deep excoriations may result. Such people are sometimes labelled as having ‘neurotic excoriations' or factitious disorder, but in fact the picking behaviour is delusionally motivated and is an irresistible urge to stem the invasion of the parasites.

Chronic cutaneous dysaesthesia (59) is an unremitting burning sensation of the skin or mucosae, sometimes generalized but at other times largely confined to complaints of glossodynia or vulvodynia. A minority of these patients appear to have a monodelusional complaint.

A subgroup of patients with trichotillomania and onychotillomania (60) have delusional illnesses, and the hair-pulling or nail-picking may be part of the attempt to rid themselves of parasites.

In all the above presentations, the delusion and its associated behaviours typically occur in the setting of many well-retained personality features and the patient can often make very clear-cut and apparently rational complaints, convincing the many physicians they attend, at least for a time, that actual physical disease is present. However, no somatic treatment works and the complaining becomes increasingly frenzied and unreasonable. The sufferer cannot be persuaded that infestation is not present and often becomes very angry at the perceived incompetence of the dermatologists he has visited.

Usually the story of the infestation is presented in great detail, perhaps involving an original event such as an insect bite. ‘Proof' is presented by displaying skin lesions, deformed nails, bald patches, etc. The ‘matchbox' or ‘pill-bottle' sign, in which the patient produces a small container in which ‘insect corpses' or ‘eggs' are kept, is typical; these nearly always turn out to be dried mucus, skin scrapings, or pieces of lint. (61) Often, there is incessant cleaning of self and surroundings, and repeated demands may be made to local authorities or pest-control agencies for disinfestation of the home. At times bizarre and even dangerous self-treatment is resorted to, such as applying boiling water or corrosive substances to the skin. The more normal part of the psyche is dominated by shame or fear of passing on the infestation, so that progressive social isolation tends to occur, with attendance on doctors as virtually the only outside activity.

Case Study: Somatic subtype with a theme of infestation

A woman of 67 was referred by a dermatologist because of ‘neurotic excoriations'. She had been seen by many physicians over a period of 10 years, complaining of worms which crawled under her skin and laid their eggs, especially around her genital region. She had an irresistible urge to scratch and dig out the ‘eggs' and as a result her genital area, buttocks, and thighs were covered with excoriations. She denied any itch and said she dug out the parasites to prevent further spread. No physical treatments had helped. On examination she was alert and showed no evidence of dementia. Her physical health was otherwise good. On most topics she could converse reasonably, but on the ‘worms' she was vehement and angrily denied they were ‘imagination'. She appeared to have an isolated delusional system of somatic type.

Dysmorphic delusions

‘Dysmorphophobia', an old term which implies a morbid fear of being deformed, is still sometimes employed to describe cases in this category but should be abandoned since it has been so loosely used to denote both delusional and non-delusional complaints as well as a variety of very different illnesses. (62) In the present context we are considering only cases typical of delusional disorder which present with a false belief of ugliness or deformity. In some instances there may indeed be some minor deformity, but the complaining is out of all proportion to this and is expressed with unremitting delusional intensity.

A specific feature is often singled out by the individual, such as an overlong nose, prominent ears, over-large or undersized breasts, dissatisfaction with the appearance of the genitalia, a skin blemish, or some other. (63) However, in other cases the total body is perceived as abnormal, and there is evidence that a small subgroup of apparent cases of anorexia nervosa and bulimia nervosa may have an underlying delusional disorder.

Many of the patients with dysmorphic delusions go from surgeon to surgeon demanding cosmetic procedures and usually being refused, but if the surgeon does not perceive the illogicality of the complaint an operation may take place. While some successes have been reported, the general consensus is that most cases need psychiatric rather than surgical intervention and that surgery may seriously worsen the mental disorder in the longer term.

It is sometimes very difficult to distinguish cases of delusional disorder of somatic subtype from severe somatization disorder, and claims have been made that there is a continuum between these illnesses. (64) The evidence for this is minimal and a diagnostic distinction is essential since treatments of the two disorders are very different.

Case Study: Somatic subtype with dysmorphic delusion

A man aged 35 was seen in psychiatric consultation on a surgical unit. He had been complaining for at least 6 years that an appendicectomy scar was so ugly that it was ruining his life, although he never let anyone other than surgeons see it. He had repeatedly sought cosmetic surgery, but every surgeon who examined him said the scar was normal. The patient gave up work, became reclusive, and ruminated endlessly on his ‘deformity'. Finally he operated on himself, trying to excise the scar, but when he lost a lot of blood he panicked and called for an ambulance. Following operation in hospital he appeared rational on every topic except the scar, was of average intelligence and denied any suicidal feelings. At first he was thought to have a factitious disorder, but his continuing conviction that his life was useless if he could not have reparative surgery proved to be delusional.

Delusion of smell or of halitosis (65,66 and 67)

In this category it is often very difficult to distinguish between delusions and hallucinations of smell. The term ‘olfactory reference syndrome' is often used to describe olfactory delusions, but in fact it should properly only refer to hallucinatory experiences. Sometimes the deluded patient will say that he or she has not actually experienced the odour, which is usually unpleasant, but ‘knows' that it is present because of remarks made by others or their avoidant behaviour. In other cases the stench is described graphically and consistently (like ‘burning rubber' or ‘faeces') and here a hallucination may be present. There may be no explanation, or else the smell may be attributed to escaping flatus, abnormal sweat secretion, or sinus or dental problems leading to halitosis etc. As is typical, an unending and escalating search for a physical treatment occurs.

Miscellaneous delusional contents

Presumably there is an almost infinite possibility of different themes, but in practice their numbers are somewhat limited. The following have been described.

Dental (68)

Although his dentition is satisfactory, the patient insists that his dental bite is abnormal and obtains repeated corrective treatments from successive dentists, none of which work. This has been termed the ‘phantom bite syndrome', and may sometimes be associated with complaints of facial pain for which no physical basis is apparent. There may also be delusional complaints of deformity of the jaw or abnormality of the temporomandibular joint.

Delusion of transmitting non-sexual diseases

Some patients may be convinced that they are causing illnesses in others (e.g. tuberculosis), and they will cite as evidence, for example, that everyone starts coughing when they walk into a room.

Delusion of sexually transmitted disease (69)

Hypochondriasis is, of course, rampant around the topic of sexually transmitted disease. A subgroup of delusional disorder patients develop the conviction that they have venereal disease, often when there is no evidence of risk-taking behaviour having occurred. In the past syphilis was probably the greatest fear, but nowadays it is usually AIDS. Repeated tests showing negative serology have no reassuring effect. Interestingly, a few cases of AIDS have been described in recent years in which a delusional illness with hypochondriasis has emerged, usually due to direct effects of the virus on the brain.

Differential diagnosis of delusional disorder: somatic subtype

First, the presence of a significant physical disorder must be excluded. The illness must be distinguished from the following: paranoid schizophrenia substance-related disorders (e.g. itching due to alcohol-related liver failure, cocaine abuse, etc.) organic brain disorders severe depressive disorder with hypochondriacal delusions somatoform disorders, especially body dysmorphic disorder obsessive–compulsive disorder factitious disorder.


Cases usually present in medical and surgical practices and much less often in a psychiatric context. We have no idea of the frequency because non-psychiatrists make a variety of diagnoses, often untranslatable in psychiatric terms. However, the somatic subtype of delusional disorder is certainly not uncommon, and this is increasingly being revealed as onsultation–liaison psychiatry develops.

These cases make a strong impression on physicians and surgeons because of their insistence and unreasonable demands. To date, dermatologists have been most aware of the nature of the delusional complaining and, in some cases, have learned to treat the deluded patients satisfactorily with appropriate medication. Infectious and tropical disease specialists also have an awareness, as do gastroenterologists and some dentists, and they are gradually referring more cases for psychiatric help. Plastic and cosmetic surgeons see a considerable number of cases with dysmorphic delusions, but it is still rather uncommon for them to seek psychiatric consultations. Since the patient with delusional disorder generally refuses to visit a psychiatrist willingly, it is often necessary for us to consult on the other specialists' territory in order to offer practical help and to obtain a better idea of the illness's frequency.

From what we know, the somatic subtype affects both sexes approximately equally and the age of onset may be from late adolescence to extreme old age. The illness is more common in the unmarried, the divorced, and the widowed.


The aetiology is discussed in the section on general aetiological considerations above.

Course and prognosis

Typically the illness is long term with a tendency to worsen with time. Some patients eventually lapse into a rather apathetic state, and some attempt or commit suicide in chronic despair, but the majority continue to demand treatment on their own deluded terms indefinitely. Treatment of the somatic subtype Treatment is discussed later in this chapter in the section on overall treatment aspects.

Delusional disorder: jealousy subtype (70,71)

This is sometimes known as the Othello syndrome, but the term is not recommended as it lacks specificity.

The phenomenon of jealousy

Jealousy can arise in various contexts, but here we shall deal with sexual jealousy. This is a virtually universal human emotion, especially when a rival is attempting to lure away someone's sexual partner. Males and females are equally prone to jealousy but may express it differently; Mullen and Martin (72) suggest that men are mainly concerned with losing the partner whereas women worry about the effect of infidelity on the ongoing relationship.

Broadly there are three levels of jealousy. Normal jealousy is understandable in terms of the situation and the individual's perception of it, and its expression can range from pique to severe rage. How it is expressed is largely related to temperament; some people habitually vent anger with slight provocation and others usually bottle up their feelings. On the whole, men tend to act out their jealous anger more physically.

Neurotic jealousy occurs where the mood and its mode of expression are relatively normal but owing to non-psychotic psychiatric illness, including personality disorder, the reaction is impulsive and excessive. Although the individual is reacting to an overvalued idea rather than a delusion, this type of jealousy can be irrational and quite persistent, and may be expressed dangerously.

Psychotic jealousy, such as occurs in delusional disorder, is characterized by a fixed delusional belief which cannot be swayed by reasoned argument or presentation of contrary evidence. This is the most alarming type since there is no dissuasion and there is an inexorability about the way that the individual accuses, controls and even stalks the victim. Since the accusations are usually untrue, the latter is bewildered by them, but occasions do arise when a partner actually has been unfaithful and it is then very difficult for the observer to know at first how much of the jealousy is justified and how much is delusional. Eventually the savageness and unreasonableness of the accusations reveal themselves as undoubtedly abnormal, but meanwhile a frightened partner will have suffered enormous abuse and possibly repeated assault.

When does jealousy become pathological?

Jealousy which appears justifiable is regarded as normal, although perhaps not laudable, and it will usually be accepted by society if its manifestations are not antisocial. Nowadays we increasingly frown on jealous violence, whether provoked or not, but in some communities there is still acknowledgement of the crime passionel, the crime committed out of jealous love. However, this is invariably an excuse extended to males, and the jealous woman who commits assault or murder is usually treated more harshly.

Cobb(70) proposed the following as clinical features of pathological jealousy, whether it be neurotic or psychotic.

  1. The jealous thinking and behaviour are unreasonable in expression and in intensity.
  2. The jealous individual is convinced of the partner's guilt but the evidence is dubious to others.
  3. A recognizable psychiatric illness is present which could plausibly be associated with abnormal jealousy.
  4. In a proportion of cases, the jealous person has habitual personality characteristics of jealousy, suspiciousness, and overpossessiveness.
  5. The jealousy persists unduly and reinforces itself.
  6. Pathological jealousy is usually focused on one specific person.

In neurotic jealousy, which in some ways resembles obsessive– compulsive disorder, there is high self-awareness of the emotion and sometimes of its irrationality. In delusional jealousy the person is totally at one with the belief which has come to occupy much of his or her time. Counter-argument or contrary evidence is rejected, yet in delusional disorder the individual may be so high functioning in other areas that he or she is totally convincing to outsiders and may even be able to brainwash the innocent victim into admission of guilt, a form of folie à deux.

The impact of pathological jealousy

Delusional jealousy is anguishing to the sufferer and even more so to the sexual partner who is accused of infidelity. The latter is subjected to escalating emotional abuse, and indignation, protest, and proof of innocence are unavailing. Physical violence, especially by males, is common (73) and in a proportion of cases finally ends in homicide, sometimes followed by the suicide of the perpetrator. (74) Subjected to prolonged threat, many victims are too terrified to speak up, and some become housebound in a vain attempt to prevent accusations of philandering. From time to time the situation reveals itself when the desperate partner attempts suicide and talks to a helping professional when recovering.

Clinical features

The person's belief in the other's infidelity is absolute and brooks no contradiction. There is much associated irritability, despondency, and, in some cases, aggressiveness. An ever-increasing proportion of time is spent searching for spurious ‘proofs', and ‘clues' are pounced upon and misinterpreted; for example, an innocent stain is believed to be semen. The victim is put through endless interrogations and is kept under constant surveillance.

Paradoxically, when the jealous individual is questioned closely about his or her specific charges, details prove vague, there is irritability, and there are self-justifying repetitive statements. Evidence is always about to be produced but rarely materializes. Strangely too, the jealous person often avoids taking the action which might provide definite proof of guilt or innocence, and this passivity in the midst of intensiveness may be evidence of some volitional defect.

As noted, delusional jealousy is more commonly reported in men, but this is probably an artefact due to their greater likelihood of violence. Also, there is a link between chronic alcohol abuse, as well as amphetamine and cocaine abuse, and delusions of jealousy, and it is known that these substance abuses are more common in males.


The overall prevalence of abnormal jealousy and the specific prevalence of the delusional disorder subtype are unknown and, because of fear on the part of the victim, both are invariably under-reported. Both heterosexual and homosexual cases occur, and family patterns of jealous behaviour have been described, but there is little evidence of direct inheritance.


Psychological, especially psychodynamic, theories of jealousy have failed to distinguish between normal and pathological forms. Freud (16) suggested that delusional jealousy was the result of an unconscious homosexual wish externalized onto the heterosexual partner and the theme of ‘latent' homosexuality is again invoked, but with little supportive evidence. Injured narcissism is another recurring speculative theme. Psychological investigations, in general, have raised many questions but provided us with no convincing answers about aetiology.

Inherited temperamental factors may be important(75) but most cases of delusional jealousy do not have a family history of the condition itself. In the jealousy subtype of delusional disorder, it may be fair to postulate a brain abnormality which can express itself over time or when provoked by chronic substance abuse or the effects of brain injury.

Of course, provocative or misunderstood behaviour by the partner may provide a context for the delusion but is never sufficient to account for the illness itself.

Course and prognosis

The condition may appear gradually or suddenly, but even when the onset seems rapid there may have been a previous period of rumination and perplexity of varying duration which probably represents the experiencing of delusional mood or Wahnstimmung. When the delusion crystallizes the perplexity vanishes and the patient is then totally sure of his belief.

Delusional jealousy is typical in being chronic and often lifelong. Without treatment the prognosis is poor and the danger to the victim is ever present. Most patients refuse to accept psychiatric treatment and unfortunately may only receive it following incarceration for a violent crime.

Differential diagnosis

The illness must be distinguished from the following:

  • actual marital or sexual problems, including spousal infidelity
  • mental handicap, where a simple-minded person may develop a ‘crush' and be unable to understand that the other person does not reciprocate, or else enters into a sexual relationship and cannot cope with the partner's motives and behaviours
  • schizophrenia, especially of the paranoid type
  • major mood disorder with delusions, either depressive or manic
  • personality disorder, especially of the paranoid, antisocial, borderline, histrionic, and narcissistic types
  • obsessive–compulsive disorder
  • substance abuse (which may complicate any of the other differential diagnoses)
  • organic brain disorders, including dementias and some epileptic disorders
  • sexual dysfunction may lead to fears that a normal partner is seeking satisfaction elsewhere.

It should be noted that an important part of the diagnostic process, an accurate collateral history, may be impossible to obtain in cases of delusional jealousy because of the victim's fears.

Forensic complications (51)

In cases of identified physical abuse in a relationship one possibility that must always be considered is delusional disorder of jealous type. Severe assault and even murder are not uncommon, and the physician has a duty to warn and protect the partner if these dangers seem real, perhaps divulging confidential information if necessary. Of course the patient denies that his beliefs are unjustified and may present his case more convincingly than the terrified victim can. If involuntary committal is necessary it may be very difficult to sustain, partly because of the individual's ability to maintain a pseudonormal facade and often because he or she threatens litigation.

Occasionally, cases of stalking, usually of females by deluded males, are jealousy related and the victim is nearly always well aware of the stalker's identity in these instances.


This will be discussed when considering the overall treatment approach to delusional disorder. If successful treatment can be achieved, the couple may require considerable psychotherapy and counselling to re-establish a trusting and fear-free relationship.

Case Study: Delusional disorder: jealousy subtype

A married man aged 47 was arrested by the police after unprovokedly attacking the minister of his church who had been paying a pastoral visit to him and his wife. It emerged that for the past 18 months he had had the growing suspicion that his wife and the minister were having a sexual affair. Lately he had been following her unseen to choir practices and had started to take days off work to observe his own house for secret visits by the minister. Although nothing untoward occurred his conviction grew and his wife reported increasingly alarming jealous outbursts at home. He apparently attacked the minister on the strength of an innocent remark he misinterpreted. On examination in a forensic psychiatric unit he was quiet, mostly rational, and showed some remorse, but still maintained that his wife was committing adultery. He admitted to heavy alcohol use as a young man but not in recent years. Otherwise his history was unremarkable and he was still holding down a steady job. He appeared to have an encapsulated delusional system with jealous content.

Delusional disorder: erotomanic subtype (76,77 and 78)

 In erotomania the individual has strong erotic feelings towards another person and has the persistent, unfounded belief that this other person is deeply in love with him or her. The belief is usually delusional, though a small number of non-delusional cases have been reported. Occasionally the imagined lover does not actually exist, but more often he or she is a real person who is unaware of the situation. The phenomenon is often referred to as de Clérambault's syndrome, but this usage is obsolete and can be misleading since it is used to describe erotomanic manifestations in a number of different mental illnesses.

De Clérambault (76) distinguished a ‘pure' or ‘primary' erotomania from other cases which were more symptomatic, and this pure form approximates to the modern description of delusional disorder with erotomanic content. In the older literature it was claimed that erotomanic delusions were largely confined to women, especially isolated and frustrated elderly spinsters, but more and more cases of male erotomania are being reported nowadays. (79,80) In both sexes the majority of cases described involve heterosexual emotions, but homosexual erotomania is now well documented in both males and females.

Clinical features

The patient yearns for another person and has the unshakeable belief that these feelings are reciprocated. The person is often socially unattainable, may be of higher social status, and can be a celebrity. There has rarely been close contact and the love object will usually be unaware of the situation, but despite this the patient believes that the other initiated the imagined relationship, often with covert signals or utterances. Many patients experience strong erotic feelings, but some insist that the relationship is platonic and that the other person is maintaining a non-sexual attitude of watchful protectiveness.

In many instances the patient makes no attempt to get in touch with the love object, perhaps writing letters or buying gifts but not sending them. When given a chance to make actual contact he or she will frequently avoid doing so and will make spurious excuses such as not wanting to offend the other person's spouse. In those cases where the patient does attempt contact, equally false reasons are presented to explain the almost inevitable rejection that results.

Since this is erotomania in the setting of delusional disorder, the illness will have the typical form of a tightly knit delusional system with preservation of relatively normal personality features and with greater or lesser ability to continue functioning in society. There is often enough insight or inhibition present for the patient to keep the delusional beliefs concealed. However, at times he or she may be profoundly angered by being ‘inexplicably' rejected and may act this out, occasionally dangerously. This is more likely to occur in males.

The onset of erotomania can be gradual or apparently sudden. Hallucinations are sometimes present but are not prominent, although the patient may be encouraged by ‘hearing' the other person express passionate feelings. Occasionally, the presence of tactile hallucinations leads the patient to believe that a lover has paid a visit during the night (sometimes picturesquely referred to as the ‘incubus syndrome') (81)

Diagnosis and differential diagnosis

Many covert examples necessarily go unrecognized and so there is a bias towards diagnosis of cases with some sort of acting-out behaviour. Otherwise the most common situation is one where the patient, after years of silent suffering, becomes unhappy enough to be treated for depression and then, during sympathetic history-taking, lets the delusional belief slip out. There is often much accompanying anguish and perhaps anger, and of course the beliefs are regarded as indisputable. Obviously, if the patient has been very secretive, a confirmatory history may be impossible to obtain. In married patients the spouse may be totally unaware of delusions which have lasted for years.

The following disorders may be associated with secondary erotomanic features.

  • Schizophrenia, especially paranoid, in which the erotomania coexists with other delusions, florid hallucinations, and more widespread thought disorder.
  • Major mood disorder, in depressive or manic phases.
  • Organic brain disorders, including epilepsy, post-head-injury states, following long-term substance abuse, senile dementia, and possibly as a side-effect of steroid treatment.
  • Mental handicap, in which misunderstanding occurs regarding another's feelings or intentions. However, we must remember that the mentally handicapped are liable to sexual abuse and we must not unthinkingly dismiss sexually laden remarks that they may make about other individuals. Conversely, we must also remember that mental handicap can coexist with psychotic disorders and delusional expressions.
  • Delusional misidentification syndrome has occasionally been described with erotomanic features.
  • Non-delusional erotomanic beliefs may emerge in unstable individuals, sometimes complicating transference in the course of psychotherapy. If associated with histrionic traits there may be florid acting out, but the beliefs do not have the qualities of a delusion.


Nothing is known of the frequency of erotomania in general, or of the erotomanic subtype of delusional disorder. As will be noted below, the more dangerous aspects of the illness are proving to be not uncommon.


Textbooks commonly cite premorbid personality characteristics of oversensitivity, isolativeness, and vulnerability, accompanied by traits of priggishness and prudery, especially in women. They may be correct but the evidence is inferential and slight. Nevertheless a stereotype has been perpetuated of lonely embittered spinsters obtaining vicarious sexual satisfaction with a delusional lover. (15) The truth is that it may be at least as common in younger males whose tendency to aggressiveness can be accentuated by a history of alcohol or drug abuse.

Course and prognosis

Without treatment this is a chronic illness which is likely to worsen gradually over time.

Forensic complications (80,82)

Males who irrationally act out their erotomanic delusions are usually diagnosed as schizophrenic but some prove to have delusional disorder. Often the overt behaviour is in the nature of harassment, but even without violence the individual's persistent intrusiveness and incorrigibility can be thoroughly alarming to the victim, who is bewildered by the situation and by the other's accusations of duplicity. (83)

Severely aggressive behaviour can lead to assault, kidnapping, and even murder, sometimes of the love object or perhaps an acquaintance of the latter who is viewed as a rival. A manifestation which has gained much recent publicity is that of victim stalking, and in a considerable number of cases the victim has no idea who is carrying out the stalking.

While women are generally less prone to aggressive acting out of their delusions, they may sometimes demonstrate their false beliefs in devastating ways. For example, a deluded woman may claim publicly that a physician, counsellor, or teacher has demonstrated strong erotic feelings towards her. This belief may be the result of a delusional memory. If she has an undeteriorated personality, is coherent, totally believes her own story, and presents it with typical vehemence and persistence, it may be virtually impossible to persuade the public and the authorities that the accusations are totally false. Any professional person dealing with deluded patients must be aware of abnormal transference emotions that may arise in the patient during treatment, usually of a heterosexual nature but sometimes homosexual. Great circumspection is then required and the therapist must immediately seek collegial help in dealing with such a situation.


Treatment is discussed later in the chapter in the section on the overall treatment of delusional disorder.

Case Study: Delusional disorder: erotomanic subtype

A woman of 53 was referred for psychiatric opinion by her family doctor because of depressive symptoms. She demanded a female psychiatrist and at first was uncooperative in giving a history. She admitted that she was unhappy and eventually broke down and told the psychiatrist that her unhappiness was due to the fact that she and her gynaecologist were in love but because of his profession he could not declare himself. When she visited his office she knew by his gestures and vocal intonations that he was covertly expressing love and she admitted having orgasmic sensations during pelvic examinations. She had never said anything to him and did not want to break up his or her marriage, but the prolonged stress of unrequited love was causing her depression. No actual depressive illness was present and the symptoms appeared to be those of a delusional disorder, erotomanic subtype. The gynaecologist was discreetly made aware of the situation via the family physician. Fortunately the patient improved with treatment and subsequently agreed to attend a different gynaecologist.

Delusional disorder: grandiose subtype (37)

This is the least well described variant of delusional disorder, not surprisingly in view of its nature. An individual who is habitually elated, even exalted, and who may believe himself or herself rich or powerful is unlikely to seek help, especially psychiatric help. If he or she remains sufficiently high functioning to function in the community, the delusions may be undetected; indeed some people capitalize on their beliefs by belonging to fringe organizations, apocalyptic religious groups, or doomsday sects. Sometimes these groups develop malignant qualities, especially under a deluded but charismatic leader, and one cannot minimize the dangerous qualities of the forceful megalomaniac whose grandiosity is alloyed with persecutory anger. Like-minded and impressionable people are readily drawn in and a kind of mass shared psychotic disorder may result; comparisons with Nazi Germany are not inapt.

Clinical features

This disorder often only emerges over time and with observation. The few cases that we see tend to fall into two categories. The first are those whose state of bliss is so profound that they totally neglect self-care. The rest are usually seen in custody after they have committed an offence under delusional influence. The characteristic underlying features of a delusional disorder have already been well described.

Differential diagnosis

The illness must be distinguished from the following.

  • Mania, in which grandiosity is associated with euphoria, overactivity, and, at times, irritability and suspiciousness. As the mood is highly volatile, the grandiose symptoms are unstable.
  • Schizophrenia in which there is marked incongruity between ecstatic affect and relative thought poverty.
  • Organic brain disorders, especially affecting the prefrontal cerebral lobes, which cause labile mood, disinhibited behaviour, and some degree of cognitive deficit.
  • Cerebral syphilis (general paralysis of the insane) used to be the best-known exemplar.
  • Antisocial personality disorder in which the individual feels above the law and may express grandiose ideas and behaviours. In these cases one finds evidence of marked impulsivity, lack of remorsefulness, and a long-standing history of delinquency.


We have virtually no information. The illness can occur in either sex and apparently at any age from adolescence onwards. It may appear gradually or suddenly.


All that can be said is that the aetiology is probably similar to that of other delusional disorder subtypes and that abnormal brain function is present. Psychoanalysis has suggested that it is due to pathologically inflated narcissism with investment of the self by libido which is usually invested in external objects, as well as a prolongation of the feelings of omnipotence said to occur in the young child. Other theorists have postulated that grandiosity represents a flight from feelings of worthlessness. (84) None of these developmental hypotheses proves helpful in dealing with the clinical case.

Course and prognosis

As far as we know, the grandiose subtype is as chronic and unremitting as the other subtypes of delusional disorder. For many years the presence of grandiosity in any psychiatric disorder has been regarded as a bad prognostic factor. In delusional disorder this may be so, because a grandiose delusional system is particularly likely to be associated with refusal to accept treatment. Even if treatment begins to be effective, the abandoning of highly pleasurable beliefs may not be welcomed by some patients. There may be forensic complications if grandiose delusions are overtly acted out.


Treatment is discussed later in the article in the section on the overall treatment of delusional disorder.

Case Study: Delusional disorder: grandiose subtype

A 78-year-old unmarried woman who had always lived alone was admitted to a geriatric medical unit after being found in unbelievably squalid circumstances. Although unable to care for herself and showing some evidence of malnutrition, she was in reasonable physical health and appeared quite personable in social situations. Her mood was cheerful but not elevated and she was non-demented. It gradually emerged that she believed herself to be a multimillionairess who did not have to care for herself because her affairs were being attended to by multiple servants. Although she appreciated that her home was filthy, she did not see any conflict in this. Her delusions were absolutely fixed but were encapsulated, and she showed marked preservation of personality features. When discussing topics other than herself she was quite reasonable and non-grandiose, and she regularly kept up to date on current affairs via the media.

Delusional disorder: mixed and unspecified subtypes

There is little to be added regarding these categories. When delusional disorder was defined in DSM-IIIR, the emphasis was on single predominant delusional themes such as those that have been described. In DSM-IV it is accepted that more than one theme can exist side by side so that, provided that the form of the illness is that of delusional disorder, it is acceptable that the delusional system may combine themes of, for example, hypochondriasis and persecution, persecution and grandiosity, erotomania and jealousy, etc.

The unspecified type is a residual category and again the illness must have the form of a delusional disorder, but the delusional content is one other than those specifically listed. No systematized data exist on either the mixed or the unspecified subtypes.

Other disorders with persistent delusions

As mentioned previously, ICD-10 has a category for ‘other persistent delusional disorders' (F22.8), but this is so loosely worded as to nullify any description as a coherent clinical entity. Under the rubric of ‘other disorders with persistent delusions' we shall now discuss two conditions, delusional misidentification syndrome and paraphrenia. Neither of these is officially recognized at present, although paraphrenia could be diagnosed indirectly as a member of category F22.8. It is suggested that both are important diagnoses which belong on the paranoid spectrum and which should be strongly considered for inclusion in it.

Delusional misidentification syndromes (DMIS) (85,86)

The abilities to recognize individual faces and to discriminate between different faces are fundamental human processes and normally we are extraordinarily adept at them. The biological need for face recognition is present from birth and the capacity elaborates throughout earlier life. Changes in a familiar facial appearance can be unsettling and even frightening, not just in children but also in adults. A great deal of sophisticated neurophysiological and neuropsychological investigation has been carried out on normal and abnormal human face-recognition abilities.

A number of clearly defined neurological disorders are associated with very specific abnormalities of face recognition. (87) Since 1923, when Capgras and Reboul-Lachaux(6) first reported the illusion de sosies or ‘delusion of doubles', there has been growing interest in abnormalities of recognition involving facial and bodily appearance and behavioural characteristics which present as psychiatric, and specifically delusional, disorders. Here we shall emphasize those cases in which a delusion of misidentification is the principal symptom of the disorder and in which the form or structure of the illness is in many ways similar to that of delusional disorder. These are the delusional misidentification syndromes. However, it is important to note that superficially similar presentations may occur as secondary features in cases of schizophrenia, severe mood disorder, or dementia, and in these we refer to a misidentification phenomenon rather than syndrome.

Clinical features (88)

There are four main variants of DMIS:

  1. the Capgras syndrome, in which the patient falsely perceives that someone in his environment, usually a close relative or friend, has been replaced by an almost, but not quite exact, double;
  2. the Frégoli syndrome, where the patient believes that one or more individuals have altered their appearances to resemble familiar people, usually to persecute or defraud him or her;
  3. intermetamorphosis, in which the patient believes that people around have exchanged identities so that A becomes B, B becomes C, and so on;
  4. the syndrome of subjective doubles, where the patient is convinced that exact doubles of him- or herself exist, a kind of Doppelgänger phenomenon.

Additional alternative forms have been described and it should be noted that features of more than one variant may occur in an individual case. This is especially true of the subjective doubles phenomenon.

Although the patient is convinced of the deception, typically he is aware that something is wrong and that the replacements are subtly incorrect. Many sufferers are extremely distressed and frightened because they are convinced that the substitution of identity is meant to harm them. In some cases they become enraged and attack the ‘impostor' with considerable violence. Their belief is of delusional intensity and they usually cannot be dissuaded by argument or by demonstration of contrary proof.

It is of particular interest that the misidentification is not indiscriminate but involves a limited number of usually familiar people. In some cases, substitution involves not just people but places or objects. An admixture of depersonalization and derealization is not uncommon, especially in the earlier stages.


Delusional misidentification syndromes have been regarded as something of a curiosity until recently and have not been included in DSM-IV or ICD-10. If a misidentification phenomenon occurs in the setting of another psychotic illness such as schizophrenia, then of course it is regarded as a feature of that illness. However, if it is the principal aspect of a psychosis then it should be regarded as a disorder sui generis. In those cases where there is a discrete delusional system occurring in clear consciousness and within a relatively intact personality, it would seem logical to assign the patients to a new status within the Delusional Disorder (DSM-IV) or Persistent Delusional Disorders (ICD-10) category. In other cases where organic brain disease is more prominent, the proper assignment would be to Mental Disorders due to a General Medical Condition (DSM-IV) or Organic, Including Symptomatic, Mental Disorders (ICD-10).

Diagnosis and differential diagnosis

The diagnosis is based on recognition of the patient's delusional belief, the accompanying agitation, and uncharacteristic behaviours, possibly including violent attacks on people in the environment. A full neurological investigation is mandatory. Differential diagnosis includes the following: schizophrenia delusional disorder, persecutory subtype major mood disorder with delusions organic brain disorder substance abuse disorders.


The frequency of DMIS is unknown. Until the past decade it was regarded as very rare, but an increasing number of cases are being reported. The disorder occurs in both sexes and across a wide age range, but particularly in middle-aged and elderly people.


When DMIS was first recognized, psychological, and especially psychodynamic, explanations were sought for the phenomenon. (89) The fact that the delusion usually involved the patient's nearest and dearest led to the theory that overintense affect towards significant others induced ambivalent feelings, leading to psychological splitting and projection, very much as in theories of paranoia. Such hypothesizing was based entirely on retrospective information, and it has been seriously undermined in recent years by the increasing recognition of significant brain pathology in a high proportion of cases. Also, it has been suggested that the majority of patients tend to be too old at the time of onset for a purely psychological origin to seem feasible. To date, psychodynamic formulation and therapy have not proved useful in practice.

Nowadays we have many reports on brain dysfunction in DMIS (32,90,91) but large case series are lacking. There is some consensus that abnormalities of the right cerebral hemisphere are especially likely to be present, particularly in the right temporoparietal area, but these are not inevitable and lesions in other cerebral locations have been noted. Currently it is acknowledged that at least two-thirds of typical DMIS cases have a demonstrable brain lesion which can be regarded as causal and which may specifically bring about abnormalities of face recognition (a function mediated especially in the right hemisphere). Also, there commonly appears to be dissociation of sensory information from its appropriate affective accompaniment and failure of suppression of inappropriately repetitive behaviours (also a right-sided function). These last two phenomena are very typical of delusional illnesses in general.

We know little of the biological substrate of delusional symptoms, but one proposal is that there may be a dysfunction of the limbic-basal ganglia mechanisms involved in their genesis, with particular emphasis on dopamine overactivity. (92) In DMIS there appears to be a breakdown in integration of information between the right parietotemporal cortex, the limbic system, and certain basal ganglia, resulting in the specific misidentification quality of the delusion, associated with inappropriate emotion and inability to suppress abnormal thoughts and behaviours. In addition, there is some evidence linking disorders of the limbic lobe with ‘paranoid' symptoms in general. Therefore it is possible to postulate a complex brain mechanism which normally integrates sensory and affective impulses and downregulates repetitive behaviour, and whose malfunction results in delusional beliefs, altered judgment, overintense mood, and inability to change or develop insight. The particular delusional content would be determined by the specific site within the mechanism at which the significant abnormality had its predominant affect.

Although the above is simply a paradigm, it is also a model with potential for the study of delusional and concomitant phenomena by modern neurobiological investigative methods. It also allows us to conjecture about the general similarities and specific differences between DMIS and delusional disorder, and perhaps it may help us with the classification of the former.

Course and prognosis

Although DMIS may appear insidiously, it not uncommonly comes on relatively suddenly in a previously normal individual, presumably related to the underlying cerebral pathology. Where brain damage is substantial, the prognosis is that of the brain disease. If the brain dysfunction is more subtle and does not remit, the delusional symptoms may become chronic. Forensic complications may occur if the patient becomes violent, (93) and a small number of murders have been reported in association with DMIS.


Acute treatment may involve sedation and antipsychotic medication. Ongoing treatment is by maintenance doses of an antipsychotic with possible addition of an anticonvulsant. Psychological counselling may be beneficial as the patient recovers.

Case Study: Delusional misidentification syndrome with Capgras and Frégoli features

A man of 63 recovered from a relatively minor stroke with only minimal left-sided weakness. During his convalescence he became very agitated and began accusing his wife of being an impostor. He also thought that visiting relatives were being impersonated by strangers and that this was all part of a plot to deprive him of his money. He frequently threatened to strike others, although he did not actually commit violence. At times he broke down and wept copiously, apologizing to his wife somewhat over-effusively. He was admitted to a psychiatric unit where an electroencephalogram and a CT scan revealed cerebral abnormalities, especially but not exclusively on the right side. His symptoms gradually improved on anticonvulsant treatment. He returned home functioning on a somewhat limited level but apparently free of delusions.

Paraphrenia (11,94)

As noted earlier, paraphrenia is a diagnosis which has fallen out of favour, but its demise has left an uncomfortable gap in the diagnostic repertoire which psychiatrists either ignore by labelling everything as schizophrenia or else ineffectually try to fill with nondescript diagnoses such as ‘atypical psychosis' or ‘schizoaffective disorder'. The ICD-10 category of ‘other persistent delusional disorder' (F22.8) could be used for cases of paraphrenia and would at least denote an illness with links to delusional disorder, but it must be made clear that paraphrenia is not simply a variant of the latter.

Clinical features

Kraepelin's description of paraphrenia (11) was of an illness similar to paranoid schizophrenia, with fantastic delusions and hallucinations but having relatively limited thought disorder and well-preserved affect. Compared with schizophrenia, there was less personality deterioration and volition was less impaired. The patient's ability to communicate with others and to demonstrate rapport and emotional warmth remained good. In contrast with paranoia (now delusional disorder), there was not the encapsulated highly organized quality of the delusional system and the delusions lacked the quasi-logical structure of delusional disorder.

There are few recent descriptions of Kraepelinian paraphrenia (95) and virtually no studies have been carried out on it in the past 60 years. However, a recent investigation by Ravindran et al. (96) appears to confirm that cases of paraphrenia can readily be recognized on predetermined criteria and can be distinguished from schizophrenia. These patients have a disorder which closely fits Kraepelin's original description. In addition, it is noted that agitation and irrational behaviour are prominent in the acute stage, usually an apparent response to vivid delusions and hallucinations. Despite resemblances to paranoid schizophrenia, less than a third had made threats or displayed aggressive behaviour prior to assessment. In fact, nearly half the patients came to notice because of illogical complaints to the authorities, indicating a breakdown in reality testing but some retention of social judgment.

When the immediate psychotic symptoms settle sufficiently to allow better communication, the preservation of emotional warmth and sociability becomes apparent and is in marked contrast to typical schizophrenia, but these individuals still show widespread thought disorder, multiple delusions, and poor insight.

Diagnosis and differential diagnosis

The principal aim is to distinguish paraphrenia from the more deteriorative aspects of schizophrenia on one side and from the encapsulated delusional system characteristic of delusional disorder on the other. Therefore other disorders to be distinguished are:

  • paranoid schizophrenia
  • delusional disorder
  • major mood disorder with delusions
  • dementia
  • severe schizoid, schizotypal, or paranoid personality disorder
  • schizoaffective disorder.

By inference it appears that cases of paraphrenia are about one-tenth as common as all other cases of schizophrenia in an inpatient psychiatric population, but this tells us nothing about its frequency in a general population. Since personality deterioration is less marked, one might expect cases of paraphrenia to survive better in the community than cases of schizophrenia and to be relatively more common there, but we have no statistics on this.

The illness occurs in both males and females, but the sex ratio is undetermined. Despite their retention of some positive social attributes, many of these patients live alone and experience considerable social isolation. Contrary to the traditional belief that this is an illness of older people, the age of onset can be at any time from early adult life to extreme old age. It is possible that paraphrenia may occur more often in immigrant groups. Schizophrenia is said to be uncommon in the family history, although psychiatric illness in general is frequent in families.


The possible association with immigration has been noted above. Many texts have declared that deafness, and to a lesser extent blindness, are potentially isolative and provocative factors, but evidence for this is uncertain. A family history of psychiatric illness occurs in perhaps half of the cases of paraphrenia and its presence seems to be associated with an earlier onset of the disorder. A prior history of substance abuse and head injury are presumed to have significance in some cases but no statistics are extant.

Course and prognosis

The illness is chronic and is progressive in many cases. Fluctuations in severity occur, but nowadays this may be related to intermittent periods of treatment alternating with non-compliance. Despite their good rapport with staff and fellow patients, paraphrenics often have poor insight and judgement about their illness. As inpatients they co-operate with treatment and usually respond well to neuroleptics, so that superficially they appear remarkably normal at the time of discharge. However, delusional thinking remains covertly active in many cases and a high proportion repeatedly relapse after discharge because they stop their medications. Fortunately many patients remain fairly undeteriorated even after several exacerbations, but in the longer term possibly as many as half will gradually deteriorate towards schizophrenia, particularly of the paranoid type. Consistent compliance with medication is likely to lead to a much more optimistic outcome.


In an acute phase the patient usually needs to be admitted for inpatient observation until stabilized on medication. The little evidence that exists suggests that paraphrenics in general respond well to all standard neuroleptics. If relapse occurs, non-compliance is a likely cause. Since the illness is potentially lifelong, the choice of neuroleptic should be influenced by the need to avoid long-term side-effects. Following discharge from hospital it is extremely important to maintain permanent supervision, even when the patient appears appear well, and to remember that these patients can utilize their retained social skills to hide their delusions and their lack of co-operation, at least for a time. The uncooperativeness is often delusionally motivated.

Case Study: Paraphrenia

A 38-year-old woman was admitted to a psychiatric inpatient unit for the sixth time in 5 years with an initial diagnosis of paranoid schizophrenia. On admission she was restless, disruptive, and grandiose, and she appeared to have severe auditory hallucinations. She had been brought to hospital because she had been virtually camping in the police station demanding action against allegedly persecutory neighbours. This hospital admission was typical of several previous ones. Each time, after some initial resistance, she accepts treatment and rapidly improves. Despite the severity and pervasiveness of her delusions, she always becomes pleasant and shows remarkable appropriateness and range of mood and a good deal of depth of affect. Rapport with others is good. At discharge she always insists she will comply with treatment, but her insight is poor and she never completely loses her delusional beliefs. Relapse is always the result of stopping her medications. Despite frequent exacerbations and chronicity of the illness, her personality remains remarkably preserved when she takes her treatment, but long-term prognosis is thought to be poor.

Late paraphrenia

This subject is considered in this article: Schizophrenia and paranoid disorders of late life

Folie à deux: a phenomenon which may accompany illnesses with delusions (97,98 and 99)

This phenomenon is listed as a psychiatric disorder in DSM-IV (Shared Psychotic Disorder, 297.3) and in ICD-10 (Induced Delusional Disorder, F24) but there is a conceptual difficulty in regarding it as a psychotic illness in its own right, as will be discussed shortly. Folie à deux is a venerable term used to describe a situation in which mental symptoms, usually but not invariably delusions, are communicated from a psychiatrically ill individual (the ‘primary patient') to another individual (the ‘secondary patient') who accepts them as truth. As noted, DSM-IV and ICD-10 refer to this by different names and there have been several confusing changes of official terminology in recent years. The older name, which is used as an alternative by DSM-IV, is well known to most psychiatrists and is used here by preference. However, à deux may sometimes be a misnomer since several people can be involved, and then we read of folie à trois, folie à plusieurs, folie à ménage, etc.

Taking the dyad as the classical situation, the two people are usually closely associated or related, especially husband–wife, siblings, or parent–child, and usually live in social isolation. The content of the shared belief depends on the predominant delusion(s) of the primary patient and can include convictions of persecution, delusional parasitosis, belief in having a child who does not exist, misidentification delusions, and many others. There have been descriptions of shared persecutory and apocalyptic beliefs in quasi-religions and cults apparently originating with a charismatic leader and coming to be shared by gullible followers. In many shared delusional constellations there is a sense of antagonism by ‘them' who may be defined or who may be what Cameron (100) referred to as the ‘paranoid pseudocommunity', the hovering ‘they' who carry out persecution which is evident to the sufferers but not to others.

Once thought rare, folie à deux has been increasingly described in the literature. Milder cases may not be recognized and, also, many delusional people strive to avoid psychiatric referral; collusion between primary and secondary patient in this has been noted. The physician should be aware of the phenomenon and not overlook it.

The current official names (above) are open to semantic criticism since ‘shared psychotic' and ‘induced delusional' disorder imply that both members of the dyad are psychotic. In delusional disorder this is certainly true of the primary patient, but the recipient of the beliefs does not usually have a psychotic illness. Most often, he or she is highly impressionable and perhaps highly dependent and adopts the untrue beliefs because of their prolonged and extraordinarily intense transmission by the primary patient. Social isolation, accentuated by induced mistrust of ‘them', prevents adequate reality testing from occurring. Thus one might say that the content of the secondary patient's false belief derives from psychotic thinking, but he or she is not usually psychotic.

Nearly all cases of folie à deux are reported in association with schizophrenia, delusional disorder, severe depressive illness with delusions, or early dementia, but it is probable that the condition also sometimes coexists with non-psychotic illnesses such as obsessive– compulsive disorder, somatoform disorder, and histrionic–dissociative personality disorder, in which the beliefs are intensely held and communicated but are not delusional. This makes the DSM-IV and ICD-10 names even less appropriate.


In practice, the great majority of cases are of the type described, often known as folie imposée because the belief is impressed on the non-deluded person by the primary patient.

However, one occasionally sees an alternative presentation, the so-called folie simultanée, in which two predisposed people develop illnesses with delusions and through long and over-close association come to share identical false beliefs. This is said to be most likely when there is a genetic link (for example two siblings) and the situation may be most common in older people who have lived together in considerable isolation for many years.


Folie à deux is included with Schizophrenia and Other Psychotic Disorders in DSM-IV and with Schizophrenia, Schizotypal, and Delusional Disorders in ICD-10, and is treated as though it were a separate psychotic illness. It would be better to treat it as an important clinical phenomenon which may be associated with other identifiable mental disorders. However, rather than encourage a pedantic argument, it is best simply to alert the clinician to its existence, its frequency, and, as will be explained, its importance.


The phenomenon is sui generis and is recognized by the identical nature of the two individuals' beliefs, their gross overinvestment of affect in these, and their refusal to accept alternatives even when proof is presented. Careful history taking will usually readily distinguish the primary from the secondary patient, but at times this proves difficult. In the much less common folie simultanée, the distinction is largely irrelevant.


This is unknown except that, by definition, it will occur most often in association with an illness characterized by delusional beliefs or severely overvalued ideas, especially under isolated living conditions, and it is by no means rare. It is extremely important for the clinician to be on the lookout for it. He or she may be convinced that a patient is expressing delusional ideas but be thoroughly perplexed when an apparently rational relative supports the unlikely belief. This can lead to serious mismanagement of the case. Conversely, recognition of folie à deux may solve a baffling diagnostic problem and result in appropriate care for both individuals.


Folie à deux appears to arise from a combination of the following:

  1. innate impressionability and marked dependence on the primary patient;
  2. personality traits such as suggestibility, low initiative, poor reality testing, etc. in the secondary patient;
  3. in some cases, low intelligence in the secondary patient;
  4. the intensity of the abnormal beliefs expressed by the primary patient;
  5. the length of time during which the abnormal beliefs are being imposed;
  6. the degree of social isolation.

Course and prognosis

This depends on the outcome of treatment (see below). Treatment In folie imposée the logical approach is to identify the primary patient and treat his or her mental disorder adequately. It may also be helpful to separate the two individuals for a time, for example by admitting the primary patient to hospital. With both people, every attempt must be made to reduce social isolation and to reintroduce them to reality. If the primary patient's delusions improve with treatment, the secondary patient's beliefs usually also improve. It is rarely appropriate to treat the secondary patient with antipsychotic medication, although this is sometimes mistakenly done.

In folie simultanée, both patients require neuroleptic or other active treatment.

Theoretically, treatment is straightforward but in practice it can be problematic. For example, in delusional disorder the primary patient often resists psychiatric help, and subterfuge and resistance by both individuals is common. In group situations, for example a cult, this resistance is likely to be widespread and intense, and will be justified by the participants in terms of religious and social beliefs which they claim are being suppressed and persecuted. The propagators should be separated from the recipients as much as possible, and the treatment team has to expend much time and diplomacy in gaining some confidence and a degree of co-operation. Direct challenge of the beliefs in any shared delusional situation is usually totally counterproductive.

Mass suicide is a reported outcome of shared delusions in some cult situations and any danger of this must be countered with great urgency. (101)

Case Study: Folie à deux

A highly intelligent man in his early fifties had had a brief sexual affair with a woman in his workplace some years before. He felt rather guilty although the liaison ended amicably and his wife did not know about it. About 3 years later he gradually became convinced that the woman involved had generated a plot against him amongst his fellow workers. He became totally preoccupied with this and eventually publicly accused her. She totally denied his charges, but in the next few months he harassed her and fellow employees incessantly, demanding ‘proof' and a ‘confession'. He was eventually dismissed and it was made clear to him by the company that they found no basis for his suspicion. For the next 2 years he spent all his time at home, endlessly retailing his constantly elaborating beliefs to his wife and neglecting all his normal routines. His equally intelligent wife had become totally convinced by him and was running a campaign with him to force the woman to admit to her alleged provocations. This had resulted in several legal actions against both of them which proved no deterrent. They reluctantly agreed to a psychiatric examination which indicated that he had a delusional disorder of the persecutory subtype and that she suffered from folie à deux. Neither accepted the need for treatment.

Treatment of delusional disorder

The treatment approaches to the delusional misidentification syndromes, paraphrenia, and folie à deux have been dealt with in their respective sections, but for several reasons the treatment of delusional disorder has been touched on only briefly until now. Firstly, it is necessary for the reader to have a grasp of the disorder's features and to know something of its status within a group of illnesses with delusions. Secondly, there are special aspects to the treatment of delusional disorder which need emphasis, especially since many clinicians are unfamiliar with them.

During the many years when paranoia was all but forgotten many psychiatric illnesses previously regarded as hopeless became readily treatable. When paranoia was again recognized—as delusional disorder—by DSM-IIIR in 1987 it seemed that the therapeutic hopelessness of an earlier era was also revived. Even now most texts state that treatment response is poor and are vague about the specifics of medication approaches. In fact, by far the greatest problem is not treatment responsiveness, but persuading the patient to accept that he needs psychiatric help because his delusions militate against this.

It must be stated categorically that, given careful diagnosis and an approach that encourages the patient to co-operate, delusional disorder is a highly treatable illness.

Unfortunately most of the literature supporting that statement is anecdotal but it shows good consensus on the remediability of the disorder. Virtually all the reports of success refer to psychopharmacological, specifically neuroleptic, treatment.

General aspects of the treatment of delusions (102)

Psychiatrists usually aim to treat the illness of which the delusion is a part, but there is good evidence that delusions themselves, as well as hallucinations, can be considerably modified by a psychological approach. In severe psychotic illnesses the institution of psychological treatment usually has to await the initial controlling of symptoms with medications or, on occasion, electroconvulsive therapy. Thereafter, a cognitive–behavioural approach or, to a much lesser extent, conventional psychotherapy can help the individual to reduce preoccupation with false beliefs, become less isolated from society, and reorientate towards reality. (18,103) However, there is no good evidence that psychological methods by themselves can completely eliminate delusions.

Since many illnesses are associated with delusions we have to tailor the psychopharmacological approach to suit each particular condition. In delusional disorder, the schizophrenias, and schizoaffective disorder, neuroleptics are the mainstay, with antidepressants, mood stabilizers, and electroconvulsive therapy sometimes playing subsidiary roles.

The rate of symptom response to treatment in a psychotic disorder is not uniform. (102) For example, hallucinations often resolve quite quickly, but delusions tend to be much more persistent. Despite vigorous treatment they can last for many months and, in some patients, never fully remit. If the patient continues to be deluded, non-compliance with treatment is likely to be present, especially in delusional disorder where the individual is often expert at concealing his or her lack of co-operation.

Treatment approach (37)

At present it appears that all the subtypes of delusional disorder are potentially responsive to treatment. If treatment fails, consider patient non-compliance first before abandoning the current approach.

The best-attested treatment results refer to the somatic subtype, with smaller literatures on the erotomanic, jealousy, and persecutory subtypes, and virtually nothing on the grandiose form. A wide variety of neuroleptics has been reported upon, but at present pimozide, a diphenylbutylpiperidine neuroleptic, is the drug of first choice.(104) Antidepressants and benzodiazepines are usually ineffective as first-line treatments and monoamine oxidase inhibitor antidepressants are contraindicated as they may worsen the delusions. There is no literature on the use of newer atypical neuroleptics in delusional disorder, but this should certainly be an area of study in the future.

Currently the best estimate of treatment outcomes, admittedly from a very scattered literature, is that, if the diagnosis is correct, the patient compliant, and the treatment adequate, recovery (defined as ‘return to full function with total or near-remission of symptoms') occurs in approximately 50 per cent of all patients, no matter which neuroleptic has been used. A further 30 per cent will show substantial but less complete improvement. If pimozide has been the specific neuroleptic the results are a little better and nearly 90 per cent of all patients are reported to be recovered or improved. An unknown proportion of the remainder have failed to improve because they have not taken the medication adequately. Although based on mostly non-blind trials these figures come from a worldwide literature which does show marked consistency in reports of recovery rates.

Practical aspects of treatment

Since so many delusional disorder patients actively resist seeing a psychiatrist, it is best to see them in a non-psychiatric setting where possible, for example in the office of the referring specialist or family physician. The physician who treats cases of delusional disorder needs much patience and tact, and it is common to spend one or more sessions first gaining the individual's confidence and finally persuading him to give a psychotropic medication a trial. Many of them argue vehemently and with well-organized pseudo-logic against the premise that they have a psychiatric illness and use all kinds of sophistry to deny the need for a neuroleptic, but a calm and persistent approach will gain co-operation in a good proportion of cases.

As pimozide does seem to have the best success rate reported so far, (105) its use is recommended, but whatever neuroleptic one prescribes it is essential to begin with the lowest effective dose (e.g. pimozide 1–2 mg daily, haloperidol 1–2 mg daily). This dose is only raised if required and then very gradually to avoid side-effects which are guaranteed to cause cessation of treatment. The patient should be seen at least once a week as an outpatient in the initial stages. Inpatient treatment is not often indicated, although forensic cases will nearly always be seen in an institutional setting.

It is not unusual to observe minor improvements in a few days, such as reduced agitation, a slight increase in well being, improved sleep, and a little less preoccupation with the delusion. On average it is about 2 weeks before the delusional system is significantly ameliorated, but in some patients this may take 6 weeks or longer.

Quite often if this degree of improvement occurs the patient decides that there is no further need for treatment and stops it. Within days or weeks there is an inevitable return of the delusion with its accompanying agitation and preoccupation. It is then that the treating physician must be available to encourage resumption of medication. Although at this stage the patient still believes in his delusions, the experience of improvement followed by relapse makes a deep impression and, given trust in the therapist, often leads to long-term co-operation.

It is striking that good recovery is often relatively rapid and can be surprisingly complete, even when the illness has been present for many years. Some patients return to a considerable degree of intrapsychic, interpersonal, and occupational functioning, with little evidence of the personality disorder that is supposed to be so prevalent in delusional disorder. Also, many patients require surprisingly little counselling or psychotherapy in resuming a reasonable life, although these should always be available if needed. Such results suggest that this profound illness may be due to a relatively circumscribed brain abnormality and also that, in some cases at least, a very insidious onset may cause initial changes which mimic personality disorder.

In most instances, treatment has to be continued for an indefinite period since delusional disorder is potentially a lifelong illness. Naturally the drug dosage should be the lowest which keeps symptoms under control and this maintenance dose is often very low indeed (e.g. 1–2 mg pimozide daily). Perhaps up to one-third of patients can eventually be weaned successfully from medication, but we have no means of predicting who these will be, so that any reduction in treatment must be carried out with extreme caution. Sadly, a proportion of relapses are due to injudicious withdrawal of treatment by a physician and we must assume the need for treatment to be permanent unless proved otherwise. It is interesting that successfully treated patients, whether on maintenance drugs or not, keep a lookout for subsequent recurrences themselves and may report that tension-inducing circumstances provoke some reappearance of symptoms. Such patients may then request to have their medication raised or resumed.

There is no necessary correlation between acquired insight into the desirability of taking one's medication and true insight into the illness itself. Many patients never fully accept the psychotic nature of their experience, but as long as they are benefiting from treatment and are functioning reasonably there is nothing to be gained from challenging them on this. If, despite treatment, the delusions remain intrusive, cognitive–behavioural therapy and counselling should be available, but exploratory psychotherapy is contraindicated.

Throughout treatment, an optimistic and encouraging attitude by the physician is essential. Early on, frequent appointments are necessary and these are scaled down as improvement occurs. In the longer term it is essential that delusional disorder patients have good ongoing supervision; an insightful family physician is excellent for this but a periodic psychiatric review is recommended.

Recognition and treatment of postpsychotic depression (37,106)

Ten per cent or more of delusional disorder patients whose illness responds to neuroleptics experience significant degrees of mood disorder during recovery, sometimes very severe and with suicidal risk.(107) Such postpsychotic depression has also been noted in recovering schizophrenics, or in a few cases, mania.

Various explanations have been proposed such as a medication side-effect or perhaps the achievement of insight which is painful. On the whole the most likely reason is neurochemical, due to rapid changes in neurotransmitter balance.

If the neuroleptic is withdrawn, the depression tends to improve but the delusions return. Therefore the proper approach is to continue with the minimum effective level of neuroleptic and to add an antidepressant drug in a full therapeutic dose. Occasionally, in extremely severe cases, electroconvulsive therapy is indicated. Subsequently the neuroleptic is continued but, in most instances, the antidepressant can be gradually withdrawn.

All cases of delusional disorder should be observed for the possible emergence of mood symptoms during recovery and treatment should be immediately instituted. If suicidal symptoms appear, admission for inpatient observation and treatment is highly recommended.


Paranoia, now delusional disorder, is unique in psychiatry in that it is virtually a newly discovered illness and yet much of the fundamental descriptive work was done a century or more ago. This long hiatus means that most practitioners have scant knowledge or experience of the disorder, and the few who are aware of it usually only see a small part of the fabric. For example, there is the dermatologist who treats a case of delusional parasitosis, the cosmetic surgeon whose difficult patient has a dysmorphic delusion, the lawyer trying to cope with a totally unreasonable litigant, the police officer faced with a jealous murderer or an erotomanic stalker, or the personnel officer who has to deal with an employee who is convinced his fellow workers are persecuting him, and many more. How can we draw all this scattered material together so as to make a whole cloth? The answer at this stage is largely by consciousness raising and education.

Delusional disorder is not rare, but there is good reason to believe that the majority of its sufferers remain in society, still functional to varying degrees, and, even if impaired and suffering, rarely agreeing to be referred to a psychiatrist. Therefore psychiatry's experience of the illness is sketchy and biased, and because of the still-prevailing belief that the illness is untreatable there is little incentive for psychiatrists to seek out cases.

This is a disorder with a considerable impact on society. Somatically deluded patients grossly overuse health services in their demands for inappropriate help. Individuals with persecutory delusions can be very disruptive in their communities, and the law and law-enforcement agencies are involved at various levels with cases which may involve assault and even murder.

To bring order out of the present chaos clinicians must learn to recognize the illness by its characteristic form, using delusional content only afterwards to define the clinical subtypes. Earlier, Jaspers was quoted as saying that delusional disorder is highly recognizable, which is very true, but too many psychiatrists are still seduced by the readily noticeable delusional content and cannot adequately discern the illness underlying it. Not only clinical work on delusional disorder but also research is being held up by lack of clarity in diagnosis.

The delusional disorder which does not yet have official diagnostic status—the delusional misidentification syndrome—has been more clearly defined of late and is being better recognized and more productively researched as a result. It sufficiently resembles paranoia/delusional disorder that one may hope that adaptations of its research methodology could usefully be applied there. This would certainly be facilitated if future DSM and ICD editions included DMIS with delusional disorder in an enlarged category.

The concept of the paranoid spectrum has been discussed earlier in this chapter, and it has been suggested that a significant gap exists in this diagnostic continuum because paraphrenia is currently being ignored. Should paraphrenia be revived in the future it is essential that it not simply be equated with ‘late' paraphrenia, a diagnosis that should probably be amalgamated with that of late-onset schizophrenia. Instead, paraphrenia, like delusional disorder, should be recognized as arising in all age groups from early adulthood onwards.

Anyone dealing with the delusional disorders must be aware of two very important associated phenomena, folie à deux and postpsychotic depression, and be able to deal competently with the problems that they pose.

Delusional disorder has much to commend it as a focus for research. It is a chronic and stable illness which may well be caused by a focal disturbance of brain function. Many of its sufferers are reluctant to take medication and so their brains are often unaffected by neuroleptics, which is unusual nowadays in a chronic psychotic illness that we wish to investigate. Those patients who do accept treatment often respond quite rapidly, enabling clear-cut studies to be undertaken on preand post-treatment states. Those who refuse are still fascinating because the encapsulation of the delusional system allows one to study abnormality and normality at virtually the same time in the same patient.

In this article we have attempted to draw together our extremely fragmented knowledge of the delusional disorders and to demonstrate that it is possible to diagnose and classify them with some assurance. Kendler, an authority in this field, has said, ‘The paranoid disorders may be the third great group of functional psychoses, along with affective disorder and schizophrenia'. (108) If he is correct, it is clear that this is no trivial task and that the well being of large numbers of patients is dependent on the physician's becoming greatly more skilled and proficient in dealing with the illnesses that have been described.

Further reading

Bhugra, D. and Munro, A. (ed.). (1997). Troublesome disguises: underdiagnosed psychiatric syndromes. Blackwell Science, Oxford.

Cash, T.F. and Pruzinsky, T. (ed) (1990). Body images: development, deviance and change. Guilford Press, New York.

Garety, P.A. and Hemsley, D.R. (1994). Delusions: investigations into the psychology of delusional reasoning. Maudsley Monograph No. 36. Oxford University Press.

Manschrek, T.C. (ed.) (1992). Delusional disorders. Psychiatric Annals, 22, 225–85.

Munro, A. (1999). Delusional disorder. Cambridge University Press.

Rix, K.J.B. and Snaith, R.P. (ed.) (1988). The psychopathology of body image. British Journal of Psychiatry, 153 (Supplement 2).

Sedler, M.J. (ed.) (1995). Delusional disorders. Psychiatric Clinics of North America, 18, 199–425.

Sharma, V.P. (1991). Insame jealousy. Mind Publications, Cleveland, TN.


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