Objective To develop and validate new classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIM) and their major subgroups.
Methods Candidate variables were assembled from published criteria and expert opinion using consensus methodology. Data were collected from 47 rheumatology, dermatology, neurology and paediatric clinics worldwide. Several statistical methods were used to derive the classification criteria.
Results Based on data from 976 IIM patients (74% adults; 26% children) and 624 non-IIM patients with mimicking conditions (82% adults; 18% children), new criteria were derived. Each item is assigned a weighted score. The total score corresponds to a probability of having IIM. Subclassification is performed using a classification tree. A probability cut-off of 55%, corresponding to a score of 5.5 (6.7 with muscle biopsy) ‘probable IIM’, had best sensitivity/specificity (87%/82% without biopsies, 93%/88% with biopsies) and is recommended as a minimum to classify a patient as having IIM. A probability of ≥90%, corresponding to a score of ≥7.5 (≥8.7 with muscle biopsy), corresponds to ‘definite IIM’. A probability of <50%, corresponding to a score of <5.3 (<6.5 with muscle biopsy), rules out IIM, leaving a probability of ≥50 to <55% as ‘possible IIM’.
Conclusions The European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for IIM have been endorsed by international rheumatology, dermatology, neurology and paediatric groups. They employ easily accessible and operationally defined elements, and have been partially validated. They allow classification of ‘definite’, ‘probable’ and ‘possible’ IIM, in addition to the major subgroups of IIM, including juvenile IIM. They generally perform better than existing criteria.
- autoimmune diseases
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This article is published simultaneously in Arthritis & Rheumatology.
FWM and LGR contributed equally,
AT and MB contributed equally.
Handling editor Tore K Kvein
Contributors All authors were involved in drafting the article or revising it critically for important intellectual content and approved the final version to be published. All authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design: IEL, AT, MB, VPW, CP, MdV, LA, AAA, RJB, MHL, JAS, KD, BMF, HK, PAL, BAL, FWM, LGR. Acquisition of data: IEL, AT, MB, VPW, CP, MdV, LA, AAA, RJB, MHL, JAS, RA, SA, HC, RGC, KD, MMD, BMF, IG-DLT, PG, TH, JDK, HK, PAL, BAL, YL, CVO, MO, AMR, LR-S, HS, AS-O, YWS, JV, SRY, FWM, LGR, The International Myositis Classification Criteria Consortium, working committee members. Analysis and interpretation of data: IEL, AT, MB, VPW, CP, MdV, LA, AAA, RJB, MHL, JAS, RA, BMF, IG-DLT, PG, HK, PAL, BAL, YL, FWM, LGR.
Funding Financial support came from the European League Against Rheumatism (EULAR), American College of Rheumatology (ACR), The Myositis Association (TMA) and in part by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences and the European Science Foundation for the Euromyositis Register, the Swedish Research Council K2014-52X-14045-14-3 and through the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet. However, the project also received support (not financial support/funding) from different associations: the American Academy of Neurology (AAN), the Childhood Arthritis and Rheumatology Research Alliance (CARRA, CARRA Inc is funded by NIH-NIAMS), Friends of CARRA, and the Arthritis Foundation, the European Neuromuscular Centre (ENMC), the International Myositis Assessment and Clinical Studies Group (IMACS), the Muscle Study Group (MSG), the Rheumatologic Dermatology Society (RDS), the Pediatric RheumatologyEuropean Society (PReS) network for JDM and the Pediatric Rheumatology International Trials Organization (PRINTO).
Disclaimer The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of the Department of Veterans Affairs or the United States government, or the NHS, the National Institute for Health Research or the Department of Health (UK).
Competing interests JAS has received research grants from Takeda and Savient and consultant fees from Savient, Takeda, Regeneron, Merz, Iroko, Bioiberica, Crealta and Allergan. JAS serves as the principal investigator for an investigator-initiated study funded by Horizon pharmaceuticals through a grant to DINORA, Inc., a 501 (c)(3) entity. JAS is a member of the executive committee of OMERACT, an organisation that develops outcome measures in rheumatology and receives arms-length funding from 36 companies; a member of the American College of Rheumatology’s (ACR) Annual Meeting Planning Committee (AMPC); Chair of the ACR Meet-the-Professor, Workshop and Study Group Subcommittee; and a member of the Veterans Affairs Rheumatology Field Advisory Committee. HC and RGC’s work in myositis is partly funded by grants from Arthritis Research UK (18474) and the Medical Research Council (MR/N003322/1). JV’s work in myositis is supported by Project (Ministry of Health, Czech Republic) for conceptual development of research organization 00023728.
Ethics approval Ethical committees at each participating centre.
Provenance and peer review Not commissioned; externally peer reviewed.
Collaborators The collaborators are included in the appendix.