Topical methoxsalen followed immediately by long-wave UV irradiation. A preliminary report on the treatment of psoriasis.

In the treatment of psoriasis with topically applied methoxsalen, the patient is exposed to long-wave UV (UV-A) energy two hours after the application of methoxsalen. Using the guinea pig as an experimental model, we found that UV-A irradiation given immediately after the topical application of methoxsalen resulted in the notable suppression of tritiated thymidine incorporation into epidermal basal cells. This finding suggests that the rate of suppression of epidermal DNA synthesis by PUVA (methoxsalen plus UV-A light) may not correlate with the interval between methoxsalen application and UV-A irradiation. This modified method of PUVA therapy (immediate irradiation) was successfully used in the treatment of psoriasis.