New Myositis Classification Criteria and Response Criteria Developed by IMACS and International Myositis Research Community

New criteria have been finalized to classify patients as having an idiopathic inflammatory myopathy (IIM) and distinguish them from other mimicking conditions. The 2017 European League Against Rheumatism (EULAR) /American College of Rheumatology (ACR)EULAR/ACR classification criteria for adult and juvenile IIM, now published and also provisionally endorsed by the EULAR and ACR, are based on a probability score in which 16 clinical and laboratory features are summed to develop a probability of having an IIM. For patients classified as having an IIM, a classification tree approach is used for sub-classification among different clinical forms, including polymyositis, inclusion body myositis, and adult and juvenile dermatomyositis. These criteria are recommended for use in research studies for patients at least 6 months from diagnosis. (Classification Criteria webpage)

A second major milestone was the recent publication of the 2016 American College of Rheumatology/European League Against Rheumatism Criteria for Minimal, Moderate, and Major Clinical Response in Adult Dermatomyositis and Polymyositis and Juvenile Dermatomyositis. The new response criteria are a conjoint analysis definition of response that provides a threshold for minimal, moderate and major clinical improvement, with different cut points used in juvenile and adult patients. The criteria use the IMACS core set measures of activity in adults, and either IMACS or PRINTO core set measures in pediatric patients, and are based on the absolute percentage change in these measures. They have been fully validated, published and are endorsed by both the ACR and EULAR. (Myositis Response Criteria webpage)

Many IMACS members contributed substantially to the development and finalization of these new classification and response criteria as part of projects that each were of more than one decade in duration.