Rituximab as an effective alternative therapy in refractory idiopathic inflammatory myopathies.

OBJECTIVES: To assess the efficacy and safety of B-lymphocyte depletion therapy (BCDT) utilising rituximab in refractory idiopathic inflammatory myositis. METHODS: We retrospectively evaluated 16 adult patients with active dermatomyositis (DM) or polymyositis (PM) who received 1 gram rituximab intravenous infusions two weeks apart after failing to respond to conventional therapy. The clinical and biochemical response were analysed by the Myositis Intention to Treat index (MITAX) and the serum creatine kinase (CK) levels at baseline and 6 and 12 months after treatment. The primary efficacy outcome was 20% improvement in the MITAX index and 30% reduction in CK. RESULTS: Eight patients responded to treatment and achieved both the MITAX and CK levels objectives within 6 months of rituximab therapy. Five out of these 8 responders remained clinically stable at 12 months and CK levels were still reduced or normalised. Of note, 4 patients who did not respond were re-assessed and had their diagnoses corrected. All patients showed adequate B cell depletion (BCD) with re-population occurring for a 15.4 months average (range 3-42 months). Those simultaneously treated with cyclophosphamide achieved more long-lasting depletion (average 18.6 months). CONCLUSIONS: The heterogeneous clinical and serological characteristics of patients diagnosed with IIM probably explain why some, but not all patients respond to rituximab. Myositis overlap and anti-synthetase syndromes seem to respond better than other patient subsets.