The mitotic index in psoriatic plaques and their response to PUVA therapy.

The mitotic index of pretreatment plaques of chronic psoriasis was determined before treatment with PUVA. There was a wide variation in mitotic indices in different patients. Treatment was given with UV-A 2 h after oral ingestion of 8-methoxypsoralen (8-MOP) two or three times per week, with increasing doses of UV-A. Patients were considered cleared if there was 95% clearing of all psoriatic plaques. There was no correlation between the mitotic index and the response to treatment, as measured by either the number of joules administered or the number of treatments until the lesions cleared. This suggests that the action of PUVA in psoriasis is not dependent on the amount of increase in epidermal proliferation.