Efficacy and safety of rituximab in anti-synthetase antibody positive and negative subjects with idiopathic inflammatory myopathy: a registry-based study.

OBJECTIVE: Post-hoc analyses of the Rituximab in Myositis trial indicate that specific autoantibodies profiles may influence treatment response. We compared the efficacy and safety of rituximab in anti-synthetase antibody (ARS-ab) positive and negative patients.

METHODS: Adult idiopathic inflammatory myopathy (IIM) subjects in the Swedish Rheumatology Quality Register who received ⩾ 1 cycle of rituximab were enrolled. Efficacy assessment was based on the International Myositis Assessment and Clinical Studies (IMACS) core set measures and the 2016 ACR/EULAR definition of improvement for PM and DM. Safety assessment included drug-related adverse event and death during study period. Comparisons were done within and between the ARS-ab defined groups before and after first and last cycles. Associations between selected clinical features and improvement after one rituximab cycle were assessed using logistic regression.

RESULTS: Sixty-five subjects were included and 43 had a follow-up visit within 5-10 months. Seventy-eight percent of ARS-ab positive subjects had moderate/major ACR/EULAR improvement after one cycle compared with 50% in the ARS-ab negative group. After several cycles, 79% of the ARS-ab positive and 67% of the ARS-ab negative patients achieved moderate/major improvement. A significant glucocorticoid-sparing effect was only observed in the ARS-ab positive group (P = 0.001). The most frequent adverse events were infections. One ARS-ab positive and two ARS-ab negative patients died during follow-up period.

CONCLUSION: Irrespectively of their autoantibody status, a majority of subjects treated with several rituximab cycles had moderate/major improvement. In addition, ARS-ab positive subjects experienced a significant glucocorticoid-sparing effect.