OBJECTIVES: The 2016 ACR-EULAR Response Criteria for JDM was developed as a composite measure with differential weights of six core set measures (CSMs) to calculate a Total Improvement Score (TIS). We assessed the contribution of each CSM, representation of muscle-related and patient-reported CSMs towards improvement, and frequency of CSM worsening across myositis response criteria (MRC) categories in validation of MRC. METHODS: Data from JDM patients in the Rituximab in Myositis trial (n = 48), PRINTO JDM trial (n = 139), and consensus patient profiles (n = 273) were included. Observed vs expected CSM contributions were compared using Sign test. Characteristics of MRC categories were compared by Wilcoxon tests with Bonferroni adjustment. Spearman correlation of changes in TIS and individual CSMs were examined. Agreement between physician-assessed change and MRC categories was evaluated by weighted Cohen's kappa. RESULTS: Of 457 JDM patients with IMACS CSMs and 380 with PRINTO CSMs, 9-13% had minimal, 19-23% had moderate and 41-50% had major improvement. The number of improved and absolute percentage change of CSMs increased by MRC improvement level. Patients with minimal improvement by MRC had a median of 0-1 CSM worsened, and those with moderate/major improvement had a median of zero worsening CSMs. Of patients improved by MRC, 94-95% had improvement in muscle strength and 93-95% had improvement in ≥1 patient-reported CSM. IMACS and PRINTO CSMs performed similarly. Physician-rated change and MRC improvement categories had moderate-to-substantial agreement (Kappa 0.5-0.7). CONCLUSION: The ACR-EULAR MRC perform consistently across multiple studies, supporting its further use as an efficacy end point in JDM trials.

Department of Pediatric Immunology and Rheumatology Wilhelmina Children's Hospital Utrecht The Netherlands

Department of Pediatrics Duke University Durham NC USA

Department of Pediatrics; Division of Rheumatology Ribeirao Preto Medical School Sao Paulo University Ribeirao Preto Brazil

Department of Rheumatology Oslo University Hospital Norway and Institute of clinical medicine University of Oslo Oslo Norway

Division of Rheumatology IRCCS Ospedale Pediatrico Bambino Gesù Roma Italy

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

General University Hospital and 1st Faculty of Medicine Charles University Prague Czech Republic

Hospital Civil de Guadalajara FrayAntonio Alcalde Guadalajara Mexico

Institute of Rheumatology Department of Rheumatology Charles University Prague Czech Republic

IRCCS Istituto Giannina Gaslini Direzione Scientifica Genoa Italy

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

Pediatrics and Adolescent Medicine Aarhus University Hospital Aarhus Denmark

School of Medicine Division of Rheumatology and Clinical Immunology University of Pittsburgh Pittsburgh PA USA

Section of Rheumatology Department of Internal Medicine Universidade Federal do Rio de Janeiro Rio de Janeiro Brazil

Section of Rheumatology Department of Medicine University of Chicago Chicago IL USA

Social and Scientific Systems Inc Durham NC USA

UOSID Centro Trial PRINTO IRCCS Istituto Giannina Gaslini Genova Italy

doi: 10.1093/rheumatology/kead110 PubMed

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