Leflunomide-induced polymyositis in a patient with rheumatoid arthritis

Although rheumatoid arthritis (RA) and myositis are major autoimmune diseases, co-occurrence of the two is rare. We treated a patient who developed polymyositis (PM) following the treatment of RA with leflunomide. Prednisolone (PSL) in combination with methotrexate (MTX) was effective in managing the PM, but the RA relapsed during the treatment. Based on the clinical course, we suspect that the PM was induced by the leflunomide treatment and suggest that clinicians should consider the possibility of this rare adverse event in cases of cholestyramine-resistant elevation of transaminases.