dermatitis herpetiformis

Pathophysiology: DH is a cutaneous manifestation of gluten-sensitive enteropathy (celiac disease). Ingested gluten triggers production of IgA antibodies against tissue transglutaminase (tTG); these antibodies cross-react with epidermal transglutaminase (eTG) in the skin, forming immune complexes that deposit in the dermal papillae, triggering neutrophil recruitment and microabscess formation, leading to subepidermal blistering.

Clinical features: Presents with intensely pruritic, symmetric, grouped (herpetiform) papules and vesicles typically on extensor surfaces—elbows, knees, buttocks, and scalp. Because lesions are so itchy, patients often present with excoriations rather than intact vesicles. Nearly all patients have some degree of gluten-sensitive enteropathy, though many are asymptomatic from a GI standpoint.

Diagnosis: Skin biopsy with direct immunofluorescence (DIF) is the gold standard, showing granular IgA deposits at the tips of dermal papillae. Serologic testing for anti-tTG and anti-endomysial IgA antibodies supports diagnosis. Histology shows neutrophilic microabscesses in dermal papillae with subepidermal blister formation.

Associations: Strongly linked with HLA-DQ2 and HLA-DQ8 haplotypes (same as celiac disease). Increased risk of other autoimmune conditions (thyroid disease, type 1 diabetes) and small increased risk of GI lymphoma if untreated.

Treatment: Dapsone provides rapid symptomatic relief (mechanism involves inhibition of neutrophil myeloperoxidase and chemotaxis) but does not treat underlying gluten sensitivity. Long-term management requires strict gluten-free diet, which addresses both GI and skin manifestations and reduces relapse risk. Monitor for dapsone side effects: hemolytic anemia (especially with G6PD deficiency) and methemoglobinemia.

High-yield boards association: DH + IgA deposits at dermal papillae tips + celiac disease + dapsone response is a classic testable triad/tetrad.