Bullous pemphigoid. Occurrence in psoriasis treated with psoralens plus long-wave ultraviolet radiation.

The occurrence of bullous pemphigoid during treatment for psoriasis has been described in the literature. We saw a case of psoriasis that was complicated by bullous pemphigoid in a patient receiving orally administered psoralen followed by long-wave ultraviolet radiation (PUVA) therapy. In our patient the localization of bullous lesions to psoriatic plaques demonstrates that the PUVA-treated psoriatic skin may have a decreased threshold for the development of clinical bullous pemphigoid. This suggests factors other than simple coexistence of the two diseases. Therapy with PUVA might induce bullous pemphigoid in psoriasis, either primarily or by facilitating the expression of a previously existing subclinical form of the bullous disorder.