OBJECTIVE: The ACR-EULAR Myositis Response Criteria (MRC) were developed as a composite measure using absolute percentage change in six core set measures (CSMs). We aimed to further validate the MRC by assessing the contribution of each CSM, frequency of strength vs extramuscular activity improvement, representation of patient-reported outcome measures (PROM), and frequency of CSM worsening. METHODS: Data from adult dermatomyositis/polymyositis patients in the rituximab (n = 147), etanercept (n = 14), and abatacept (n = 19) trials, and consensus patient profiles (n = 232) were evaluated. The Total Improvement Score (TIS), number of improving vs worsening CSMs, frequency of improvement with and without muscle-related CSMs, and contribution of PROM were evaluated by MRC category. Regression analysis was performed to assess contribution of each CSM to the MRC. RESULTS: Of 412 adults with dermatomyositis/polymyositis, there were 37%, 24%, 25%, and 14% with no, minimal, moderate, and major MRC improvement, respectively. The number of improving CSMs and absolute percentage change in all CSMs increased by improvement category. In minimal-moderate improvement, only physician-reported disease activity contributed significantly more than expected by MRC. Of patients with at least minimal improvement, 95% had improvement in muscle-related measures and a majority (84%) had improvement in PROM. Patients with minimal improvement had worsening in a median of 1 CSM, and most patients with moderate-major improvement had no worsening CSMs. Physician assessment of change generally agreed with MRC improvement categories. CONCLUSION: The ACR-EULAR MRC performs consistently across multiple studies, further supporting its use as an efficacy end point in future myositis therapeutic trials.

Department of Dermatology Stanford University School of Medicine Redwood City CA USA

Department of Neurology Brigham and Women's Hospital Harvard Medical School Boston MA USA

Department of Rheumatology 1st Medical Faculty Institute of Rheumatology; Charles University Prague Czech Republic

Division of Rheumatology Department of Medicine Solna Karolinska Institutet Karolinska University Hospital Stockholm Sweden

Environmental Autoimmunity Group Clinical Research Branch National Institute of Environmental Health Sciences NIH Bethesda MD USA

Hospital General de Occidente de la Secretaría de Salud and Universidad de Guadalajara Department of Immunology and Rheumatology Mexico

IRCCS Istituto Giannina Gaslini UOSID Centro Trial Reumatologia Pediatria 2 PRINTO Genoa Italy

Juvenile Myositis Pathogenesis and Therapeutics Unit National Institute of Arthritis Musculoskeletal and Skin Diseases National Institutes of Health Bethesda MD USA

Medical Research Center Institute of Human Environment Interface Biology Department of Internal Medicine Seoul National University

National Institute for Health Research Manchester Biomedical Research Centre Division of Musculoskeletal and Dermatological Sciences Manchester University NHS Foundation Trust The University of Manchester Manchester UK

Section of Rheumatology at University of Chicago and Division of Rheumatology and Clinical Immunology Department of Medicine University of Pittsburgh Pittsburgh PA USA

Social and Scientific Systems Inc Durham NC USA

doi: 10.1093/rheumatology/kead111 PubMed

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