Concomitant psoriasis and bullous pemphigoid: coincidence or pathogenic relationship?

Psoriasis vulgaris and bullous pemphigoid represent two clinically well-characterized, chronic, inflammatory skin diseases. The concomitant occurrence of these two entities in a patient is rare, and the pathogenic implications of this phenomenon are unknown. We describe a 55-year-old woman with a 25-year history of plaque-type psoriasis who presented with disseminated tense bullae. Skin biopsies showed the typical histologic and immunohistochemical traits of bullous pemphigoid, and she had circulating immunoglobulin G (IgG) antibodies against the basement membrane zone, specifically the BP180 antigen. The bullous eruption was successfully treated with oral methylprednisolone and dapsone. Bullous pemphigoid is the autoimmune blistering disease that has most often been associated with psoriasis. Forty cases have been described in the literature. Classical psoriasis and psoriasis associated with bullous pemphigoid are identical. The pathogenic relationship between psoriasis and bullous pemphigoid is unclear. It has been postulated that the autoimmune process responsible for bullous pemphigoid lesions may be induced by ultraviolet light therapy, topical corticosteroids, and/or the inflammatory processes that occur in psoriasis. Immunomodulatory therapy may positively influence shared as well as distinct inflammatory mechanisms in patients who have psoriasis and bullous pemphigoid.