Methotrexate induced false photosensitivity reaction.

Methotrexate is now being used in the treatment of a variety of intractable rheumatologic conditions. We report a patient with polymyositis who developed mild erythroderma after sun exposure. Forty-eight h later he received his weekly dose of methotrexate. Within 24 h the resolving rash erupted into an intense dusky red dermatitis with eventual formation of confluent bullae. The patient had a methotrexate induced ultraviolet reactivation reaction also known as a "false photosensitivity" reaction. This reaction has been reported in dermatologic publications but not in the rheumatologic literature.