Irritable Bowel Syndrome

Article about irritable bowel syndrome, which is a combination of intermittent abdominal pain and constipation, diarrhoea, or bouts of each, that occurs in the absence of other diagnosed disease.

Cause and incidence 

The precise cause of IBS is unknown, but anxiety and stress tend to exacerbate the condition. IBS affects about one in five people at some time in life and accounts for more referrals to gastroenterologists than any other disorder. It is twice as common in women as in men and the disorder is generally found to begin in early or middle adulthood.

Symptoms and signs

Symptoms of IBS include intermittent, cramplike pain in the abdomen; abdominal distension, often on the left side; transient relief of pain by bowel movement or passing wind; a sense of incomplete evacuation of the bowels; excessive wind; passage of mucus; diarrhoea; constipation; and nausea. Some people also have symptoms unrelated to the digestive tract, such as headache, back pain, and tiredness. Symptoms are typically intermittent, and usually recur throughout life, though they may become less frequent and severe with time. The condition is unlikely to lead to complications.

Diagnosis and treatment 

There is no single test to diagnose IBS as opposed to another disorder of the digestive tract. In order for a diagnosis of IBS to be made, a patient must have had continuous or recurrent abdominal pain or discomfort for at least 12 weeks accompanied by at least two of the following features: relief of pain on defaecation; onset of pain associated with a change in stool frequency; and onset of pain associated with a change in stool consistency.

IBS can sometimes be controlled through a change in diet and use of relaxation techniques. An individual may need to experiment to find the approach that works best. If constipation is the main problem, a high-fibre diet or bulk-forming agents, such as bran or methylcellulose, may be helpful. Short courses of antidiarrhoeal drugs may be given for persistent diarrhoea. Antispasmodic drugs may be prescribed to relax the contractions of the digestive tract and relieve abdominal pain. Hypnosis, psychotherapy, and counselling have proved effective in some cases.

Read more: a series of articles about irritable bowel syndrome:

Irritable bowel syndrome in more detail


Symptoms suggestive of disturbed lower gastrointestinal function without adequate explanation are very common in adults in the Western world, up to 15% of whom experience such symptoms at any one time, although most do not seek medical advice. It is not clear whether the symptoms of those individuals who do seek medical help have a different pathophysiological basis from those who do not, and whether the seeking of medical advice is more an indication of a worried individual than of disturbed gut function.

The currently used terms are best viewed as an attempt to provide some clinically useful rather than pathophysiologically accurate categorization of patients and their symptoms. The ‘Rome criteria’ recognize (1) irritable bowel syndrome, characterized by abdominal pain that is relieved by defecation with associated change in frequency in defecation and/or stool consistency; (2) functional bloating; (3) functional constipation; (4) functional diarrhoea; and (5) functional abdominal pain.

Routine haematological and biochemical screening is usually done on the assumption that they will be normal. Features that raise the suspicion of organic disease and indicate a need for further investigation include the onset of symptoms in middle-aged or older individuals, weight loss, or blood in the stool.

Management remains empirical: no single pharmacological agent or group of agents has ever been found to be consistently effective. The principal task of the physician is to give explanation and reassurance (sometimes supplemented by psychological treatments), but particular symptoms are often treated as follows: (1) constipation—defecation may be eased by supplementary dietary fibre and poorly absorbed fermentable carbohydrates which increase faecal bulk and soften the stool; osmotic laxatives and enemas are used for the severely constipated patient with slow transit; (2) diarrhoea—attention to diet is often helpful, as are simple antidiarrhoeal agents; (3) abdominal pain—antispasmodics (e.g. hyoscine butyl bromide) are frequently employed, as are low doses of antidepressants.

Irritable bowel syndrome and functional bowel disorders in detail - technical

Introduction and definition of terms

Over the last century many attempts have been made to categorize functional bowel disorders. It is not surprising that most have failed to stand the test of time, as the symptoms suffered by the patient (although genuine and troublesome) are often difficult to define, variable in their expression, and defy pathophysiological explanation. The latest and perhaps most comprehensive attempt has been made by a working group whose recommendations, known as the ‘Rome criteria’, are now accepted as a consensus view and provide a useful research tool. Whether these criteria will be better than previous attempts will, however, depend upon whether they turn out to provide a better understanding of the pathogenic mechanisms of the disease or to aid its therapy. The Rome Working Group (who are now in their third iteration of their classification) has suggested the division of functional bowel disease into a number of symptom-based categories (Bullet list 1 below). Because they do seem to have some practical value in guiding approaches to management, this chapter is based on some of the Rome categories, with emphasis on those previously encompassed by the term ‘irritable bowel syndrome’. However, it must be recognized that the Rome criteria do not necessarily include all symptoms presented by patients with abnormal bowel function. Failure to allocate a patient into one or other category should therefore not be taken to mean that the patient does not have a functional bowel disorder.

Irritable bowel syndrome


This syndrome is characterized by the presence of abdominal pain associated with defecation, or a change in bowel habit, together with disordered defecation and the sensation of abdominal distension. For practical purposes, its recognition relies upon the presence of abdominal pain that is relieved by defecation and of an associated change in frequency in defecation and/or stool consistency.

Bullet list 1 Categorization of functional bowel disease according to the ‘Rome criteria’

  • Functional bowel disorders
  • Irritable bowel syndrome
  • Functional abdominal bloating
  • Functional constipation
  • Functional diarrhoea
  • Functional abdominal pain

These criteria are themselves based on the studies of Manning and of Kruis, which identified that the above features were reported most frequently in patients with bowel problems but were very unusual in patients with structural disease of the colon.


The recognition of irritable bowel syndrome is clinically based, and relies on a carefully taken history and examination, there being no specific endoscopic, radiological, or laboratory investigation that is yet capable of providing a positive diagnosis. Despite the absence of a specific pathological indicator, the identification of irritable bowel syndrome is usually not difficult, and in most cases it is unnecessary to investigate the patient extensively in an attempt to exclude other, more serious disease.

Clinical features


In addition to the careful elicitation of the above specific symptoms, other features may be found that serve to increase clinical confidence. For example, many patients have upper-gut symptoms, e.g. food-related abdominal distension. Women may also complain of menstrual and bladder symptoms, and there is also an increased prevalence of psychosexual problems.


Clinical examination is important. Although there is no physical abnormality that is diagnostic of irritable bowel syndrome, a number of features occur commonly. Palpation over the site of the lower colon, particularly in the left iliac fossa, may produce discomfort, and a sigmoid colon containing faeces is often palpable. Similar tenderness may be present under the rib margins and in the right iliac fossa.

Rectal examination and sigmoidoscopy should be conducted as part of the initial clinical assessment. Characteristic findings are the presence of pellety stools in the rectum and a mucosa of normal appearance, evidence of mucosal inflammation is incompatible with the diagnosis. A further helpful pointer is the response to air insufflation during the sigmoidoscopy; abdominal discomfort is often reproduced and relieved by air expulsion. Evidence of a pigmented rectal mucosa (melanosis coli) may be found in patients who have been taking stimulant laxatives and is a useful indicator of the chronicity of the problem.

Further laboratory investigations remain at the discretion of the clinician, depending upon the confidence with which a clinical diagnosis is made. Routine haematological and biochemical screening is usually done on the assumption that they will be normal, and thus to provide reassurance both to the patient and the doctor. Radiological and endoscopic examination of the colon is not mandatory unless a clinical suspicion of a structural colonic disorder, particularly neoplasia, remains after the history and examination have been completed.

Features that raise the suspicion of organic disease and indicate a need for further investigation include the onset of symptoms in middle-aged or older individuals, weight loss, or blood in the stool. The development of new colonic symptoms in a patient with a long history of irritable bowel syndrome should also be taken seriously, as there is no evidence that the syndrome protects against the development of other disease and the incidence of colonic neoplasia increases with age.


Despite much interest and many painstaking clinical studies, our understanding of the pathophysiology of irritable bowel syndrome remains limited and the following hypotheses are discussed solely as a guide to current thinking.

Neuromuscular dysfunction

The most popular hypothesis is that these patients have a disorder of neuromuscular function of the gastrointestinal tract. However, although this seems eminently plausible, evidence is lacking. Manometric studies of the colon do show an increased contractile activity in patients with this syndrome, particularly after food, but the neurophysiological basis of this finding and its relationship to symptoms remains to be determined.

Visceral hypersensitivity

Another currently popular hypothesis is that visceral sensation from the gastrointestinal tract is somehow enhanced in these patients. This idea is based on the observation that distension of the rectum and colon produces greater discomfort than in people with normal bowel function. This increased sensory awareness appears to be viscerally specific, as cutaneous responsiveness is normal. However, it remains to be determined whether the mechanism for this hypersensitivity is peripheral (abnormal mechanoreceptor responsiveness in the gut) or central (abnormal sensory processing by the brain and spinal cord) or even both.

Psychiatric disease

There is convincing evidence that psychiatric disease and abnormal illness behaviour are more prevalent in patients with irritable bowel syndrome. The relationship between the psychological problem and any neuromuscular abnormality remains uncertain, although it is recognized that a heightened awareness of visceral sensation is a feature of affective disorders, particularly depression.


It is customary to regard diet as being a pathogenic factor and to attribute constipation symptoms to fibre deficiency, on the basis that irritable bowel syndrome is uncommon in those parts of the world where a high-fibre diet is consumed. While it is true that faecal bulk can be increased by ingesting more fibre and that constipation is improved, careful studies of fibre intake and symptom development do not show a clear causal relationship. Food ‘allergy’ or ‘sensitivity’ is occasionally confused with irritable bowel syndrome because abdominal pain and diarrhoea can accompany both problems. Classic food allergy with measurable immunological alterations in response to a particular food (e.g. eggs, shellfish) is readily distinguishable from irritable bowel syndrome by a clear relationship between ingestion of the implicated food and symptom development. More subtle forms of food intolerance (e.g. lactose intolerance, fructose intolerance that produce gut symptoms without an accompanying immune response are much more difficult to recognize because the nutrient in question is often present throughout the diet. Recognition requires a painstaking dietary history and the clear demonstration of a relationship between symptoms and food intake. In most patients such a relationship is not found.

Functional bloating


This is characterized by symptoms of abdominal fullness or distension, awareness of audible bowel sounds, and excessive flatus with no evidence of either maldigestion and malabsorption or excessive consumption of poorly absorbed fermentable carbohydrate.


Distension of the colon at sigmoidoscopy characteristically produces greater discomfort than normal, suggesting increased gut sensitivity. However, there is no evidence that intestinal gas production is increased. As in irritable bowel syndrome, the prevalence of psychological disorders is high.

Clinical features

The clinical assessment of such patients is identical to that for irritable bowel syndrome and features will be identical.

Functional constipation


This is arbitrarily defined as either persistently difficult, infrequent defecation or the sensation of incomplete defecation. Usually, two or more of the following are present: straining at defecation; lumpy or hard stools; the sensation of incomplete evacuation; and two or fewer bowel movements per week.

Clinical evaluation

As with the other categories of functional bowel disorders, its recognition is based on a carefully conducted history and examination designed to exclude the possibility of more serious colonic disease, particularly cancer. When considering the problem, it is important to enquire about immobility, concomitant drug therapy (particularly opiate analgesia), and a low-roughage diet, all of which are well recognized as contributing to constipation, particularly in infirm individuals.

An abnormality of pelvic-floor function on attempted defecation is an unusual cause of constipation that should be suspected in individuals who feel the need to defecate but cannot expel faeces despite severe straining. Such a problem should be considered when symptoms develop following pelvic trauma or difficult childbirth. Clinical evidence of diabetes, hypothyroidism, and hypercalcaemia must also be sought, as these may also lead to altered colonic function and constipation.

Physical examination should include a rectal and vaginal examination. The absence of perineal descent on straining is a simple indicator of impaired pelvic-floor relaxation, while descent below the level of the ischial tuberosities indicates pelvic-floor weakness. Sigmoidoscopy is required to identify the presence of formed faeces, and to exclude faecal impaction and organic obstruction of the lower colon and rectum.

Laboratory examination

Extensive laboratory investigation is usually unnecessary in the absence of clinical indicators of systemic disease and in the presence of the above criteria. A plain abdominal radiograph is often helpful to confirm the presence of faecal material throughout the colon and to allow estimation of the diameter of the small intestine and colon, which helps to exclude the rare cases of intestinal pseudoobstruction and megacolon caused by intestinal myopathies and neuropathies.

Transit studies using radio-opaque markers are commonly performed as part of the investigation of constipated patients to determine the severity of transit delay, and to distinguish those with a pancolonic abnormality from a more localized problem of pelvic relaxation. However, measurement of whole-gut transit should not be regarded as necessary for the diagnosis—documented infrequent defecation is usually sufficient. The electrophysiological and radiological assessment of anorectal function is only indicated if there is evidence of abnormal perineal descent or rectal prolapse, as the accurate recognition of pelvic-floor dysfunction can influence the choice of therapy. Such investigations are indicated when Hirschsprung’s disease is suspected.


The cause of functional constipation is uncertain. Factors likely to be of relevance are similar to those proposed for irritable bowel syndrome, in particular enteric neural dysfunction.

In the mildest cases, dietary fibre deficiency may be relevant; however, in the more severely affected patients, fibre supplementation does not abolish the problem and may even worsen symptoms, making a causal role for fibre untenable in such individuals. By contrast, a histological abnormality of the enteric nerves of the colon or muscle of the colon may be found in the most severe cases; for the great majority of constipated patients, however, no structural abnormality has been identified.

In a proportion of patients, almost invariably female, defecatory dysfunction appears to be the major factor. A failure of the pelvic-floor muscles to relax on attempted stool expulsion is identifiable in these patients; this appears to be a ‘learned’ phenomenon with a psychophysiological aetiology rather than peripheral nerve dysfunction. In other patients, low tone in the pelvic floor and rectal prolapse appear to be the result of damage to the pudendal nerve from straining at stool or parturition and thus may be a consequence of the constipation rather than its cause.

In some severely affected women there is a relationship between symptom severity and the luteal phase of the menstrual cycle, which has led to the suggestion of a sex-hormonal aetiology. In support of this hypothesis is the fact that colonic muscle tone is reduced by progesterone and that constipation is a frequent accompaniment of normal pregnancies. Against the hypothesis, however, is the failure to demonstrate abnormal colonic sensitivity to progesterone in constipated women, leaving the possibility that the menstrual cycle-related events are merely the expression of a normal cyclical progesterone effect on a malfunctioning colon.

Functional diarrhoea


This is defined as the frequent passage of unformed stool without the presence of other features of irritable bowel syndrome. Neither abdominal pain nor the frequent passage of formed stools is included in the symptoms.

The diagnosis of functional diarrhoea depends on the presence of two or more of the following: unformed stool; three or more bowel movements per day; and increased stool weight, more than 200 g/day.

Clinical features

This disorder is recognized only after excluding other, more medically serious conditions, in particular inflammatory bowel disease and secretory diarrhoeas. The possibility of surreptitious laxative use should always be borne in mind. Some patients identify the time of onset of the problem to a specific life event, particularly a bout of severe gastroenteritis. The possibility of a chronic intestinal infection needs to be considered carefully in such patients, although evidence of an infective agent will be lacking in most and the label ‘postinfective diarrhoea’ is usually applied.

Physical examination should determine the extent of nutritional deficiency, exclude metabolic disorders such as hyperthyroidism, and rule out intraabdominal structural abnormalities. Careful examination of stool samples for pathogens and laxatives is required.

Laboratory investigations

Unlike the other functional diseases, it is important to make a careful search for a structural mucosal disease in such patients. Key diagnoses that must be excluded are chronic malabsorption due to pancreatic insufficiency or gluten sensitivity, inflammatory bowel disease, infections, and infestations of the gastrointestinal tract.


In the absence of any definable structural abnormality, functional diarrhoea is generally assumed to be a disorder of neuroenteric control of intestinal epithelial transport.

In some patients, there is a clear relationship between psychological state and symptoms, with diarrhoea worsening whenever anxiety occurs. However, whether the relationship is truly causal is unknown.

Functional abdominal pain


While this symptom category is commonly included amongst the functional bowel disorders, the relationship between the abdominal pain and a disturbance of gastrointestinal tract function is difficult to ascertain. Abdominal pain is frequent, recurrent, or continuous, and characteristically persists for many months. The relationship between pain and recognizable physiological events such as eating, defecation, or menstruation is lacking, and evidence of organic disease in the abdomen is absent. Most of these patients show a major loss of daily functioning capacity and exhibit chronic illness behaviour.

Management of functional bowel disorders

The management of patients with functional bowel disorders remains empirical. Perhaps it should not be surprising that in an area of human suffering with such symptom diversity and in which the pathophysiological mechanisms remain obscure, no single pharmacological agent or group of agents have ever been found to be consistently effective.

A review of randomized, double-blind, placebo-controlled trials for the treatment of irritable bowel syndrome examined 43 trials and concluded that none offered convincing evidence that any therapy was effective, a conclusion which is perhaps as much a reflection of the difficulty of trial design as the efficacy of the drug therapy. Furthermore, in a condition in which the patient’s mental state plays such an important part in defining symptom severity, it is not surprising that in most clinical trials placebo responses have been very high, usually up to 50%. Also, short-term trials of therapeutic agents in diseases where symptoms are intermittent may be unable to distinguish a true drug effect from a placebo response.

So what can the clinician do to help patients with functional bowel disease? As in all chronic problems without a cure, a principal task is to give an explanation and reassurance. Therapy must be patient-centred and designed to provide a solution for the patient’s personal needs and expectations. The clinician should give a full explanation of the likely nature of the problem and firm reassurance that organic disease is not likely to be present. Attention to the patient’s psychological state is very important, as it is clear that mood is a powerful modulator of symptoms.

In more severe cases of irritable bowel syndrome, psychological treatment using a variety of techniques has been found to provide greater improvement in a patient’s sense of well being than drug therapy alone. Good prognostic factors for improvement seem to be overt psychiatric symptoms, particularly anxiety or depression, together with intermittent pain exacerbated by stress. In contrast, patients in whom the abdominal pain is constant, and who exhibit evidence of chronic illness behaviour, do not seem to be helped by a psychotherapeutic approach although they may respond to antidepressants.

In mild cases, attention to the individual and his/her symptoms is usually the approach taken. In patients with predominant constipation, supplementary dietary fibre and poorly absorbed fermentable carbohydrates increase faecal bulk, soften the stool, and may ease defecation. On occasion, however, this approach can exacerbate symptoms of abdominal distension, probably as a result of increased colonic gas produced by the fermentation of the unabsorbed carbohydrate. Wherever possible, long-term use of stimulant laxatives is best avoided because of the concern that such drugs may themselves damage the colonic enteric-neural function and eventually make the problem worse. Osmotic laxatives and enemas are the mainstay of therapy of the severely constipated patient with slow transit.

For the patient who appears unable to relax the pelvic floor musculature on attempted defecation, a variety of biofeedback techniques are now available that help the individual to ‘relearn’ the process. Patient satisfaction is high in those able to engage closely with the therapist in the process.

For patients with diarrhoea-predominant symptoms, attention to diet is also often helpful, as the size of and timing of meals is likely to influence the frequency and social inconvenience of the diarrhoea. Fermentable carbohydrates are best taken in moderation because they can exacerbate symptoms. In the more persistent cases of diarrhoea, symptoms can be improved by simple antidiarrhoeal agents, the dose being adjusted according to the symptoms and administered before a meal.

In the management of patients with unexplained abdominal pain it is tempting to prescribe opiate-derivative analgesics. These are unlikely to be of benefit in the long term, however, and may even exacerbate symptoms because of their constipating effect. Antidepressants are often prescribed empirically in low doses, with evidence of benefit at least in mood elevation. Antispasmodics (e.g. hyoscine butyl bromide) are frequently employed. Although there are undoubtedly a number of patients and doctors who are convinced of their value, a beneficial effect has yet to be proven beyond doubt by clinical trial. Outside Europe, 5-HT3 antagonists are becoming increasingly used for severe diarrhoea-predominant irritable bowel symptoms.

Relaxation therapy, in particular hypnosis, seems to benefit those individuals who are prepared to participate. In the right conditions, programmes of self-delivered ‘autohypnosis’ may offer a satisfactory approach for some sufferers.

Surgical intervention for symptoms of functional bowel disorders is usually best avoided, as benefit is unlikely. On occasions, however, subtotal colectomy and ileorectal anastomosis will provide symptomatic benefit in carefully selected patients with severe constipation.

Further reading

Afzalpurkar RG, et al. (1992). The self-limited nature of chronic idiopathic diarrhoea. N Engl J Med, 327, 1849–52.

Christensen J (1992). Pathophysiology of the irritable bowel syndrome. Lancet, ii, 1444–7.

Creed F, et al. (2003). The cost-effectiveness of psychotherapy and paroxetine for severe irritable bowel syndrome. Gastroenterology, 124, 303–17.

Creed F, et al. (2005). Outcome in severe irritable bowel syndrome with and without accompanying depressive, panic and neurasthenic disorders. Br J Psychiatry, 186, 507–15.

Drossman D (2006). The functional gastrointestinal disorders and the Rome III process. Gastroenterology, 130, 1377–91.

Klein KB (1988). Controlled treatment trials in the irritable bowel syndrome: a critique. Gastroenterology, 95, 232–41.

Kruis W, et al. (1984). A diagnostic score for the irritable bowel syndrome: its value in the exclusion of organic disease. Gastroenterology, 87, 1–7.

Longstreth GF, et al. (2006). Functional bowel disorders. Gastroenterology, 130, 1480–92.

Manning AP, et al. (1978). Towards a positive diagnosis of the irritable bowel. Br Med J, 2, 653–4.

Read NW, Timms JM, Barfield LJ (1986). Impairment of defecation in young women with severe constipation. Gastroenterology, 90, 53–61.

Wexner SD, et al. (1992). Prospective assessment of biofeedback for the treatment of paradoxical puborectalis contraction. Dis Colon Rect, 35, 145–50.

Whorwell PJ, Prior A, Faragher EB (1984). Controlled trial of hypnotherapy in the treatment of severe refractory irritable bowel syndrome. Lancet, ii, 1232–4.