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Methotrexate-induced papular eruption following treatment of psoriasis.

Mebazaa A, Kenani N, Denguezli M, Ben Salem C, Ziadi S, Sriha B, Belajouza C, Nouira R

Department of Dermatology, Farhat Hached Hospital, Sousse Tunisia.

OBJECTIVE: To report a case of a diffuse papular eruption following treatment of psoriasis with methotrexate injections. CASE REPORT: A 52-year-old woman presented with an extensive flare of psoriasis associated with joint pain, especially in her knees and elbows. She was treated with intramuscular injections of methotrexate 20 mg/wk. Ten hours after the second methotrexate injection, the patient experienced a diffuse pruritic papular eruption located mainly on the limbs. Histology showed foci of dyskeratosis in the mucosal layer and a polymorphic perivascular inflammatory infiltrate of the papillary dermis, suggesting a drug-induced skin reaction. According to the Naranjo probability scale, the papular eruption was probably caused by methotrexate. The drug was discontinued and papular lesions gradually disappeared. DISCUSSION: Methotrexate-induced papular eruption is rarely reported shortly after beginning methotrexate therapy in patients with acute exacerbation of collagen vascular diseases. Methotrexate-induced papular eruption following treatment of psoriasis has not been previously reported. CONCLUSIONS: The pathogenesis of methotrexate-induced papular eruption in collagen vascular diseases may suggest cutaneous small-vessel vasculitis. In our patient, histology showed aspects of drug-induced skin reaction without vasculitis. Pathogenesis of methotrexate-induced papular eruption in psoriasis may involve immune mechanisms other than those of methotrexate-induced cutaneous vasculitis in collagen vascular disease.

Published 7 January 2008 in Ann Pharmacother, 42(1): 138-41.
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