Dermatitis herpetiformis: pathognomonic transglutaminase IgA deposits in the skin and excellent prognosis on a gluten-free diet.

Dermatitis herpetiformis (DH) is an itchy, blistering skin disease with sites of predilection at the elbows, knees and buttocks. Although DH is mostly asymptomatic, all patients exhibit small bowel villous atrophy or at least coeliac-type inflammatory changes. Deposition of immunoglobulin A (IgA) in the papillary dermis is a key diagnostic feature of DH. Epidermal transglutaminase (TG3) is the antigen for IgA deposited in the skin, and tissue transglutaminase (TG2) is the antigen for IgA deposited in the small bowel mucosa. Clinically silent, but immunologically active coeliac disease in the gut appears to result in IgA TG3 antibody complexes aggregated into DH skin. The prevalence of DH in northern Europe is high (30-75/100,000), but its incidence is decreasing, possibly due to increased recognition of subclinical coeliac disease. The rash and small bowel heal on a gluten-free diet, which is a life-long treatment. The risk of non-Hodgkin's lymphoma is increased, but in patients with DH who adhere strictly to a gluten-free diet long-term prognosis is excellent.