Psoriasis occurring predominantly on warts. Possible involvement of interferon alfa

We describe a patient who developed psoriasis predominantly on the lesions of warts. After therapy with etretinate, all psoriatic lesions resolved completely, leaving only the warts. An intralesional injection of interferon alfa resulted in the rapid development of psoriatic lesions on the warts located on the dorsal aspect of the hand, as they were before therapy was started. Two injections with interferon alfa induced onset of psoriasis on warts located on the wrist. Psoriasis had not developed in this location previously. Interferon alfa may play an important role in the development of psoriasis.