Randomized pilot trial of betaINF1a (Avonex) in patients with inclusion body myositis.

BACKGROUND: Inclusion body myositis (IBM) is the most common acquired disease of muscle in adults over the age of 50 years. Although there is compelling evidence for the importance of immunologic abnormalities in its pathogenesis, the cause of the disease is not known, and it is considered to be resistant to treatment with corticosteroids and other conventional immunosuppressive agents. beta-Interferon (betaIFN), an immunomodulatory cytokine, is a candidate therapeutic agent for IBM.

METHOD: A 24-week, multicenter, randomized, placebo-controlled, parallel-group clinical trial of 30 microg of beta-interferon-1a (betaINF1a) administered IM once a week in 30 patients with IBM was conducted. The primary goal was to establish the safety and tolerability of betaINF1a in IBM. A secondary goal was to obtain preliminary data on the efficacy of betaINF1a by measuring changes from baseline in muscle strength and muscle mass.

RESULTS: Twenty-nine of the 30 subjects enrolled completed the study. Two subjects (one in the placebo group, one in the betaINF1a group) experienced severe adverse events. One subject, randomized to receive betaINF1a, died from an ischemic bowel after resection of a colonic mass. No subjects required dosage reductions, and the adverse event profile was similar for the placebo and betaINF1a groups. There were no significant differences in the changes in muscle strength and muscle mass between the placebo and betaINF1a groups at 6 months.

CONCLUSIONS: betaINF1a at a dose of 30 microg/week IM is well tolerated in IBM. Further studies are needed to establish its therapeutic usefulness in this inflammatory myopathy.