Bullous pemphigoid and dermatitis herpetiformis: mixed bullous disease or coexistence of two separate entities?

We present a 73-year-old man with a 5-year history of dermatitis herpetiformis who developed lesions with the clinical, histologic, and immunologic features of bullous pemphigoid. Direct immunofluorescence testing of a skin biopsy demonstrated both granular deposition of IgA, predominantly in the papillary bodies, and linear deposition of IgG and C3 at the basement membrane zone. This mixed direct immunofluorescence pattern, typical for dermatitis herpetiformis in the type of IgA deposits, but also typical for pemphigoid in the linear localization of IgG and C3, is unusual. This case emphasizes that even after a specific diagnosis has been established, if the clinical morphology or response to therapy changes, repeat histologic and immunofluorescence studies may be indicated in diagnosis and management of patients with bullous disease.