Management of dermatitis herpetiformis

Dermatitis herpetiformis (DH) is a vesiculo‐bullous disease with a characteristic clinical picture. The diagnostic hallmark is the demonstration by direct immunofluorescence of IgA deposits in the dermal papillae of uninvolved skin. The diagnosis should not be made without this finding. Patients with DH have an associated gluten sensitive enteropathy and overwhelming evidence has been presented over the last 30 years that gluten causes both the rash and the enteropathy of DH in genetically predisposed individuals. Nearly all patients with DH have the histocompatibility antigens HLA B8 DR3 and DQw2 and associated target specific autoimmune disease. The management of DH has to be directed at control of the rash, identification of the severity and treatment of the associated gluten sensitive enteropathy and identification and treatment of associated autoimmune disease. The rash of DH responds impressively to oral therapy with dapsone. Itching subsides within 24 h of starting treatment and new lesions stop appearing after 48 h. Cessation of therapy leads to recurrence of the rash. The use of dapsone is limited by its side‐effects. It is a powerful oxidizing agent and in therapeutic dosages of about 100 mg daily causes a chemical haemolysis. Elderly atherosclerotic patients will not tolerate even moderate degrees of haemolysis. Dapsone also has idiosyncratic side‐effects such as headache and lethargy. These unwanted effects lead to withdrawal of dapsone therapy in about 25% of patients in whom it is prescribed and substitution with a sulphonamide such as sulphapyridine or sulphamethoxypyridazine, usually brings about adequate control. Once the rash is controlled it is important to establish the minimum drug requirements as many of the toxic side‐effects are dose dependent. The severity of the associated gluten sensitive enteropathy is variable ranging from symptomatic coeliac disease to a mild abnormality of permeability. Patients with DH should be placed on a strict gluten‐free direct (GFD). After approximately 6 months the minimum drug requirements start to fall and patients are usually able to withdraw completely from drug therapy after about 2 years on the diet. The GFD controls the rash of DH regardless of the severity of associated enteropathy and has to be maintained indefinitely. The most common autoimmune associations of DH are thyroid disease and pernicious anaemia. Annual monitoring of serum autoantibodies is important to identify patients at risk.