Two patterns of skin ulceration induced by methotrexate in patients with psoriasis.

Two patterns of skin ulceration occurred in patients receiving weekly methotrexate for psoriasis. In type I ulceration, psoriatic plaques became painful and eroded shortly after starting methotrexate (MTX) (median, 10 days). Type II ulcers occurred in clinically uninvolved skin affected by other pathology--stasis dermatitis in two and adjacent to an anal fistula in one and had a variable relationship to the duration of methotrexate treatment. Type I ulcers developed at methotrexate doses between 12.5 and 25 (median, 20) mg/wk and healed rapidly (median, 10 days) after dose reduction or withdrawal. Type II ulcers developed at methotrexate doses of 7.5 to 20 (median, 10) mg/wk and took a median of 9 weeks to heal. Type I ulceration may be confused with an exacerbation of psoriasis, and the MTX dose mistakenly increased rather than reduced. Type II ulcers can mimic stasis ulcers and may be overlooked as evidence of MTX toxicity.