Polymyositis associated with infliximab treatment for rheumatoid arthritis

To the Editor: Therapies using anti-tumor necrosis factor (TNF)α hold the promise of exciting new strategies for the treatment of rheumatoid arthritis (RA). Although the anti-TNFα antibody infliximab has been shown to be efficacious, well tolerated, and safe, very rare reports have described induction of autoimmune phenomena (anti-double standard DNA [dsDNA] antibodies) and development of systemic lupus erythematosus. In addition, polymyositis (PM) develops on rare occasions with the use of infliximab. We report on the first confirmed case in Japan. A 52-year-old Japanese woman had a 33-year history of severe, disabling, and seropositive destructive RA with radiological changes and pulmonary fibrosis, and had recently received treatment with the nonsteroidal anti-inflammatory drugs methotrexate (6mg/week) and prednisolone (2mg/ day). Erythrocyte sedimentation rate (ESR) was 82mm/h. C-reactive protein (CRP) level was 2.5mg/dl. KL-6 level was 471IU/ml (normal, <500IU/ml), and was not indicative of the severity of interstitial pneumonia (IP). Serum aminotransferase levels were within normal ranges. No previous history of any muscular disorder was identified. The patient was started on infliximab in May 2004 following the standard regimen (3mg/kg, intravenous administration, weeks 0, 2, and 6, and then every 8 weeks) in association with methotrexate (6mg/week) and prednisolone (2mg/ day). After the third course of injections, marked clinical improvement was observed, and ESR and CRP levels de-