Disseminated superficial actinic porokeratosis in a patient undergoing treatment with long-term narrowband ultraviolet B for psoriasis.

Disseminated superficial actinic porokeratosis (DSAP) is a subtype of porokeratosis, thought to be clonal disorder of keratinization. Chronic exposure to ultraviolet (UV) light might be an etiological cause of DSAP, of which frequent sites are sun-exposed areas. We report a case of DSAP that occurred on the trunk of a 79-year-old man with psoriasis treated with narrowband ultraviolet B (NB-UVB) for clearing and maintenance therapies. DSAP has been reported to associate with psoralen and ultraviolet A therapy and broadband UVB, but not NB-UVB. This may be the first case of DSAP after repeated exposure to NB-UVB.