Pityriasis rubra pilaris (PRP) often has a devastating impact on the lives of patients. Descriptions of its histopathologic features are not uniform. Finding a successful therapy can be challenging.

Our purpose was to examine the histopathologic features and response of patients to our standard therapy of an oral retinoid and concomitant or later addition of low-dose weekly methotrexate.

A retrospective chart review was done on 24 patients with PRP seen from March 1986 to March 1996. Biopsy specimens from 19 patients were reexamined. Telephone follow-up was conducted to determine maintenance of remission.

All patients had the adult acquired form of PRP. Biopsy specimens from nine patients were characterized by prototypical findings of PRP, while the others included both typical and other features. Twenty-two patients were treated with either isotretinoin, 40 mg twice daily, or etretinate, 25 to 75 mg/day. Six patients with more disabling involvement had low-dose weekly methotrexate ranging from 5 to 30 mg started concurrently. Five patients had weekly methotrexate added at a later time. Seventeen patients showed 25% to 75% response after 16 weeks of therapy. All patients whose skin cleared maintained their remission.

Initial oral retinoid plus concurrent or later low-dose weekly methotrexate resulted in 25% to 75% improvement of PRP in 17 of 24 patients after 16 weeks of therapy. Some of the atypical features seen in biopsy specimens emphasize the importance of clinical and histopathologic correlation in establishing the diagnosis.