Background/Purpose: The treatment of idiopathic inflammatory myopathies (IIM) is challenging, complicated by its rarity and heterogeneity. Currently few studies have suggested the efficacy of RTX in refractory idiopathic inflammatory myopathies (IIM). The interpretation of their findings is hampered by the lack of a uniform and restrict criteria of refractory myositis. Herein, we established rigorous definition of refractory. The objective of this study was to evaluate efficacy and predictors of clinical improvement of RTX treated-refractory IIM.

Methods: This prospective single-center study included 25 consecutive adult patients with refractory IIM [7 anti-synthetase syndrome, 12 dermatomyositis (DM), 6 polymyositis (PM) – Bohan & Peter, 1975] from 2011 to 2015. Refractory myositis was defined by an inadequate response to prednisone ≥ 0.5mg/kg/day for ≥ three months and at least two other immunosuppressive or immunomodulatory drugs (azathioprine, methotrexate, cyclosporine, leflunomide, mycophenolate mofetil and/or human intravenous immunoglobulin, in their full-dose, for a minimum period of three months). These patients received two infusions of RTX (1g each, two weeks apart). After RTX initiation only one immunosuppressive was maintained and prednisone dose was tapered gradually. In six months evaluation, clinical improvement was defined as a 20% in at least three of the following six core set measures of disease activity: physician’s and patient’s global assessment of disease activity, manual muscle testing (MMT8), physical function (HAQ), muscle enzymes, 

Results: The mean age of patients was 40.2±11.2 years, with 57.7% Caucasian, 88.5% female gender and mean disease duration of 6.4±3.2 years. Forty percent had antisynthetase (of these, 28% anti-Jo-1), 12% anti-Mi-2 and 12% other subtypes. The majority of the patients (74%) achieved clinical response. Comparison of study entry and six months after RTX revealed a reduction in mean glucocorticoid dose (26.1±16.9mg/day vs. 17.2±16.3mg/day P=0.008) and improvements of physician’s [5.0 (4.0-6.0) vs. 4.0 (2.0-5.0), P=0.01) and patient’s global assessment [5.0 (3.0-7.0) vs. 5.0 (2.0-5.0) , P=0.045) , MMT8 [70.0 (58.0-74.0) vs. 76.0 (64.0-78.0), P=0.006), HAQ [ 1.1 (0.9-1.9) vs. 0.9 (0.3-1.5), P=0.02), creatine kinase [481(98-1261)U/L vs. 236 (84-487)U/L, P=0.042], aldolase [5.3 (4.4-14.1)U/L vs. 4.1 (3.2-6.1)U/L, P=0.002). Further analysis of responders vs. non-responders at baseline identified that autoantibodies were more frequently detected in responder patients (75.0% vs. 12.5%, P=0.004). 

Conclusion: Our study provided evidence of short-term RTX treatment efficacy for refractory IIM. We also confirmed and extended previous observations in overall IIM that myositis autoantibodies is also predictor of RTX treatment response for refractory IIM.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/myositis-specific-autoantibodies-predictors-of-short-term-good-outcome-in-rituximab-treated-refractory-idiopathic-inflammatory-myopathies/