[Bullous pemphigoid on a healed herpes zoster : A rare example of an isotopic response]

Wolf's isotopic response describes the eruption of a secondary, pathogenically independent skin disease within the borders of a primary, already healed skin disease. The exact mechanism is unknown, but the restriction to diseases with a known T‑cell component in the pathogenesis suggests an involvement of persistent local immune activation. We report the case of an 87-year-old woman who developed bullous pemphigoid lesions within the boundaries of a previous, already healed herpes zoster C7-C8, which had been diagnosed clinically and treated 2 months previously. Histopathological examination revealed subepidermal blisters, and indirect immunofluorescence showed IgG antibodies against the basal membrane zone. Both BP 180 and BP 230 enzyme-linked immunoassays (ELISAs) were positive. Based on these findings, we diagnosed a bullous pemphigoid arising on the site of the already healed herpes zoster, linked by an isotopic response.