Response of psoriasis to twice weekly PUVA

In the U.K., PUVA treatment for psoriasis is usually given three times weekly, with the starting dose of UVA chosen according to the skin type of the patient. Observations on the time-course and dose-response characteristics of PUVA erythema suggest that larger doses of UVA could be used safely, provided that the frequency of PUVA treatment is reduced. We have examined this by treating 100 patients with chronic plaque-type psoriasis with a PUVA protocol in which treatment using oral 8-methoxypsoralen was given twice weekly, with the starting dose of UVA based on each patient's minimal phototoxic dose, and with weekly UVA dose increments calculated as a percentage of the dose used in the previous treatment. Clearance of psoriasis was achieved in 92% of patients. The median number of treatments required for clearance was 12, and the median cumulative UVA dose for clearance was 52J/cm2. Although erythema occurred at some stage during the course of PUVA in 48% of patients, in only 16% of cases was the erythema of sufficient intensity to result in more than one treatment being missed. These results compare favourably with previous studies in which treatment was given three or four times weekly. Thus, twice weekly PUVA treatment for psoriasis is at least as effective as treatment given more frequently, and may be safer, as lower cumulative UVA doses are required for clearance. It also allows for more efficient operation of a PUVA unit and is more convenient for patients.