P.21.5 Progress report on the development of new classification criteria for adult and juvenile idiopathic inflammatory myopathies

Abstract

On behalf of the members of the International Myositis Classification Criteria Project. An international, multidisciplinary collaboration, the International Myositis Classification Criteria Project (IMCCP), supported by ACR and EULAR, was established to develop and validate new classification criteria for adult and juvenile IIM and its major subgroups. Candidate variables were selected from published criteria and inclusion criteria in 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. Crude pair-wise associations among all measured variables and between each variable and clinicians’ diagnoses were assessed. Explored approaches were: 1. Traditional: case defined by specified number of items from a set. 2. Probability score: case assigned a probability score by summing score-points associated with a set of variables. 3. Classification tree: case defined by a decision tree Internal validation using bootstrap methods was performed. Data from 973 IIM patients (74% adults; 26% children) 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, or better than, the classification tree that was developed (sensitivity 88%, specificity 72%, and correctly classified 84%) and published criteria. New classification criteria for IIM with readily assessable measurements and symptoms have been developed that generally show superior performance compared with existing criteria.