Dermatitis herpetiformis (DH) is a chronic autoimmune blistering disease and the dermatologic manifestation of celiac disease, occurring in 10–20 percent of celiac patients. The cutaneous and intestinal manifestations are linked by a common immunologic mechanism: dietary gluten triggers production of IgA antibodies against tissue transglutaminase 2 (TG2, intestinal) and epidermal transglutaminase 3 (TG3, skin); IgA-TG3 immune complexes deposit at dermal papillae and trigger neutrophilic inflammation and subepidermal microabscesses leading to blister formation.
Epidemiology: prevalence 11.5 per 100,000 in Northern European populations (Finland highest), male predominance 1.5–2:1, peak onset 30–40 years (can occur in childhood and elderly); strong HLA association with HLA-DQ2 (90 percent) and HLA-DQ8 (5 percent), identical to celiac disease; family clustering common.
Clinical: symmetric grouped (herpetiform = clustered like herpes) papulovesicles, urticarial plaques, and excoriations because the intense pruritus often destroys vesicles before patients present (excoriations may be the only visible finding); classic distribution on extensor surfaces — elbows, knees, buttocks, sacrum, posterior neck, scalp, shoulders; mucosal involvement rare. Associated conditions: celiac disease (essentially universal subclinically — duodenal biopsy shows villous atrophy in 65–75 percent, partial in remainder), other autoimmune diseases (Hashimoto thyroiditis, type 1 diabetes, vitiligo, alopecia areata, pernicious anemia, Addison disease), enteropathy-associated T-cell lymphoma (rare but increased risk), small bowel adenocarcinoma. Diagnosis: skin biopsy from non-affected perilesional skin shows granular IgA deposits at the tips of dermal papillae on DIF (pathognomonic); H&E shows neutrophilic microabscesses at dermal papillae and subepidermal blisters; serology: IgA anti-TG2 (anti-tTG, screening), IgA anti-endomysial antibodies (EMA, confirmatory), IgA anti-deamidated gliadin peptides (DGP), IgA anti-TG3 (most specific for DH but less available); duodenal biopsy may be deferred if classic skin biopsy and positive serology.