Characterization of a subgroup of patients with dermatitis herpetiformis with nonclassical histologic features.

Dermatitis herpetiformis (DH) is an autoimmune disease mediated by IgA antibodies. The diagnosis of DH is based on clinical presentation, biopsy for hematoxylin and eosin, and direct immunofluorescence. The chief hematoxylin and eosin finding is a subepithelial blister with neutrophils in dermal papillae. The direct immunofluorescence findings are deposition of IgA and sometimes C3 at the basement membrane with accentuation in dermal papillae. Immunofluorescence is thought to be a sensitive and specific assay in DH, and there are no other known diseases with this pattern of immunofluorescence. The aim of this project was to determine the prevalence of nonclassical histologic findings in DH. We studied 24 cases of DH received at our institution. All cases had clinical findings of DH as well as positive direct immunofluorescence with IgA. We found that 9 of 24 cases (37.5%) had nonspecific H&E findings of a lymphocytic infiltrate only with fibrosis in the dermal papillae and ectatic capillaries. The remaining 15 cases had classic findings of multilocular neutrophilic microabscesses in the dermal papillae. These findings were reproduced on step sectioning. These findings suggest that routine histology may be quite nonspecific in DH and direct immunofluorescence or other more specific immunologic assay is an essential adjunct to diagnosis.