Background Inadequate classification criteria for IIM are a fundamental limitation in clinical studies. An international, multidisciplinary collaboration, the International Myositis Classification Criteria Project (IMCCP), supported by ACR and EULAR, was established to address this problem.
Objectives Develop and validate new classification criteria for adult and juvenile IIM and its major subgroups.
Methods Candidate variables were selected from published criteria and inclusion criteria in controlled trials of myositis. Comparator conditions confused with IIM were defined.
Clinical and laboratory data from IIM and comparator patients were collected from 47 rheumatology, dermatology, neurology and pediatrics clinics worldwide from 2008-2011.
Crude pair-wise associations among all measured variables and between each variable and clinicians’ diagnoses were assessed. The explored approaches were:
Traditional: case defined by specified number of items from a set of variables
Probability score: case assigned a probability score by summing score-points associated with a set of variables
Classification tree: case defined by a decision tree
Internal validation using bootstrap methods was performed.
Results Data from 973 IIM patients (74% adults; 26% children), representing subgroups of IIM, and 629 comparators (81% adults; 19% children) were obtained. Two probability score models were developed: Model 1 comprised clinical variables on muscles, skin, and laboratory measures; Model 2 additionally comprised muscle biopsy variables. Model 1 performed nearly as well as Model 2 (specificity 87% vs. 88%, sensitivity 89% vs. 89%, and correctly classified 87% vs. 89%). Both models performed as well as, and often better than, the classification tree that was developed (sensitivity 88%, specificity 72%, and correctly classified 84%) and published criteria.
Conclusions New classification criteria for IIM with readily clinically assessable measurements and symptoms have been developed. They generally show superior performance compared with existing criteria. External validation is in progress.
Disclosure of Interest None Declared