Dermatitis Herpetiformis

Dermatitis herpetiformis (DH) is an intensely itchy, chronic blistering eruption caused by cutaneous IgA deposition and gluten sensitivity; it is the cutaneous manifestation of coeliac disease.

• Prevalence is 1 to 4 per 10,000, more in northern Europeans. Onset in 20 to 40 years, male predominance (1.5 to 2:1).
• HLA-DQ2 and DQ8 are present in nearly all. IgA anti-epidermal transglutaminase (TG3) deposits in the dermal papillae.
• Most patients have villous atrophy (often asymptomatic). Associated with autoimmune thyroid disease, type 1 diabetes, and an increased risk of small bowel lymphoma and non-Hodgkin lymphoma.

• Symmetrical, grouped, intensely itchy papulovesicles on extensor surfaces (elbows, knees, buttocks, shoulders, scalp). Often excoriated, with vesicles rarely seen intact.
• Burning or stinging before lesions appear. Oral and palmar involvement are rare.
• Gastrointestinal symptoms may be mild or absent; also iron deficiency, osteoporosis, dental enamel defects.

• Perilesional (normal appearing skin adjacent to a lesion) biopsy for DIF: granular IgA deposits in the dermal papillae (diagnostic).
• Lesional biopsy: neutrophilic microabscesses in the papillae with subepidermal clefting.
• Serology: tissue transglutaminase IgA, endomysial IgA, and epidermal transglutaminase IgA (while on a gluten containing diet).
• Duodenal biopsy if serology is positive, for baseline villous atrophy.
• Check G6PD, full blood count, ferritin, B12, folate, TSH, bone density.
• Exclude linear IgA disease, bullous pemphigoid, scabies, atopic dermatitis, and prurigo.

• Dapsone 25 to 50 mg daily, increasing in 25 mg steps weekly to 100 to 200 mg to control symptoms; response within 24 to 72 hours. Check G6PD beforehand. Monitor full blood count (haemolysis, methaemoglobinaemia), reticulocytes, liver tests, and peripheral motor neuropathy. Dose is reduced to the minimum after the gluten free diet takes effect.
• Sulfasalazine 1 to 4 g/day or sulfapyridine 500 mg to 1.5 g daily for dapsone intolerance.
• Strict lifelong gluten free diet is the definitive therapy; the rash may take 6 months to 2 years to settle off dapsone. Dietitian input, avoidance of excess iodine, and family screening.
• Topical potent steroids for itch, treatment of osteoporosis, and monitoring for lymphoma if symptoms of malabsorption persist.