Epidermal dystrophy. Occurrence after psoriasis therapy with psoralen and long-wave ultraviolet light.

Focal dystrophy of epidermal cells has been recognized in about half of 37 patients treated with psoralen and long-wave ultraviolet radiation (PUVA) for psoriasis. This lesion appeared in many patients by the end of the clearing phase of therapy and was present to a similar degree one year after the beginning of the treatment. It is probable that most such changes are transient, but the appearance suggests the possibility that cells have undergone somatic mutation that potentially could be dangerous.