Dermatitis herpetiformis is a chronic skin disease in which clusters of tiny, red, intensely itchy blisters occur in a symmetrical pattern, most commonly on the back, elbows, knees, buttocks, and scalp. It usually develops in adult life and is believed to be related to coeliac disease, a condition in which the lining of the small intestine reacts to gluten, a constituent of wheat, rye, and some other cereals.
Dermatitis herpetiformis is a manifestation of coeliac disease, although the connection was unrecognized until the 1960s.
Aetiology, genetics, pathogenesis, and pathology
Dermatitis herpetiformis is gluten dependent. However, the mechanism by which gluten causes the skin to blister is unclear. The only autoantibodies that distinguish it from coeliac disease are IgA epidermal transglutaminases, and it may be an immune complex-mediated disease. There is a strong association with HLA DQ2 or 7, and 10% of patients have a family history of dermatitis herpetiformis or coeliac disease. The frequency of this condition is highest in western Ireland, Scandinavia, and Hungary. It is rare in non-European populations. Methods to reduce the incidence of coeliac disease would be predicted to reduce the incidence of dermatitis herpetiformis.
The onset is usually sudden in young adults, although childhood cases are common in Italy and Hungary, and older people can present with it. Small, intensely itchy papules and vesicles develop on the extensor surfaces of the knees, elbows, buttocks, and trunk. In partially controlled disease the lesions are often found on the scalp and chin. The lesions are so intensely itchy that it is rare to see an intact blister. There may be other autoimmune diseases present.
Histology of a fresh lesion shows papillary microabscesses filled with neutrophils. Direct immunofluorescence testing demonstrates granular deposits of IgA in the papillary dermis, which are essential for diagnosis. As in coeliac disease, antiendomysial and antitransglutaminase antibodies should be sought, and the patient investigated for malabsorption and other autoimmune diseases.
The treatment of choice is a gluten-free diet although the malabsorption improves within weeks, the skin will not usually clear until after 2 years of strict gluten avoidance. The ingestion of gluten causes recurrence of the itching and lesions. Dapsone or sulfonamides (sulfamethoxypyridazine or sulfapyridine) will switch off the disease in 24 to 48 h, and may be slowly reduced as the gluten-free diet takes effect. Remission is dependent on strict gluten avoidance, and those electing not to have gluten-free diet will need lifelong treatment. There is an increased susceptibility to lymphoma.