Histopathology of psoriasis treated with zinc pyrithione.

Psoriasis is still a relatively poorly understood inflammatory dermatosis that is resistant to many therapies. Because the pathogenesis is poorly understood, rational treatment is elusive. Until recently, the North American public was able to achieve successful resolution with an over-the-counter topical preparation marketed for dandruff and seborrheic dermatitis called SkinCap, which has now been withdrawn from the market. The purpose of this study was to examine the histologic changes induced by this preparation in a well-developed psoriatic plaque. Serial punch biopsies were taken over a 2-week period during which time SkinCap was applied topically twice daily. The biopsies were examined histologically, and features were evaluated semiquantitatively. The classic histologic features of psoriasis resolved completely over 2 weeks, with the reversal beginning with disappearance of neutrophils and the most striking finding being prominent apoptosis at 48 hours. The mechanism of this normalization is unknown. Hypotheses include blockage of cytokine and growth factor effect at some level and induction of apoptosis.