[Bullous scabies and scabies-triggered bullous pemphigoid]

Two patients were admitted to our hospital with tense blisters on an erythematous base, typical for bullous pemphigoid. In both patients an infestation with Sarcoptes scabiei was diagnosed by dermatoscopy as well as histological examination. In one patient the clinical diagnosis of bullous pemphigoid could be confirmed by immunofluorescence microscopy, histopathology and a clinical relapse of bullous pemphigoid without scabies infestation. In the other patient no evidence for an autoantibody-mediated autoimmune blistering disease was found. We postulate that bullous scabies could develop after long persistency of the parasites leading to a specific immune response with activation of T helper type 2 (Th2) cells causing high levels of the cytokine interleukin 5 and then consecutively eosinophilia. Secretion of proteolytic enzymes near the basal membrane zone might explain the development of intraepidermal, often suprabasal blisters. In contrast, in the first patient the scabies infestation might have triggered a flare up of the underlying autoimmune disease. Comparison of our two patients demonstrates two entities: bullous pemphigoid triggered by scabies as a Koebner phenomenon and a bullous subtype of scabies mimicking bullous pemphigoid. Therefore both, scabies infestation triggering bullous pemphigoid and bullous pemphigoid-like scabies should be included in the differential diagnosis of vesicles, tense blisters and erythema, especially at an early clinical stage.