Reactivation of phototoxicity test for psoralens plus ultraviolet A by low-dose methotrexate.

Reactivation of a solar burn has been reported after administration of methotrexate for cancer and psoriasis patients. We report a case of psoriasis with a similar but delayed elicitation of phototoxic reaction by administration of low-dose methotrexate one month after psoralen and long-wave ultraviolet light (PUVA) treatment. The reactivation was seen in an already receding phototoxicity test area but not in a less phototoxic, noninterval PUVA treated area, suggesting that the reactivation by methotrexate is related with the severity of light-induced skin inflammation.