Performance of the 2017 European Alliance of Associations for Rheumatology/American College of Rheumatology Classification Criteria in Patients With Idiopathic Inflammatory Myopathy and Anti–Melanoma Differentiation–Associated Protein 5 Positivity

Abstract

Objective This study aimed to evaluate whether the 2017 European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIMs) could appropriately classify the diagnosis in adult patients with anti–melanoma differentiation–associated protein 5 (anti–MDA-5)–positive IIM. In addition, this study sought to determine whether a status of anti–MDA-5 positivity could be incorporated into the EULAR/ACR IIM classification criteria set and whether the recently modified criteria based on the presence of myositis-specific autoantibodies (MSAs) could be used to appropriately classify the diagnosis in patients with anti–MDA-5–positive IIM. Methods Consecutive adult patients clinically diagnosed as having anti–MDA-5–positive IIM from 10 hospitals in Hong Kong were retrospectively recruited; patient characteristics were obtained from electronic medical records. We used a commercial line blot immunoassay to detect MSAs. We also determined a proposed set of phenotypic-serologic classification criteria specific for anti–MDA-5. Results In the patient cohort (n = 120; 31.7% with dermatomyositis, 68.3% with clinically amyopathic dermatomyositis [CADM]), the diagnosis could be classified with the EULAR/ACR criteria in 86 patients (71.7%) and with the Bohan and Peter criteria in 49 patients (40.8%). However, when combined with criteria specifically modified for CADM, the diagnosis could be classified by the Bohan and Peter criteria in 76.7% of patients. We observed that the sensitivity of the EULAR/ACR criteria could be improved to 98.3% if anti–MDA-5 antibody–positive status was considered as one of the criteria. The MSA-based criteria had 100% sensitivity. When we applied our proposed specific phenotypic-serologic criteria for the classification of patients with anti–MDA-5 antibodies, 97.5% of patients were able to be classified as having IIM. Conclusion In this cohort of patients with anti–MDA-5–positive IIM, the diagnosis could not be classified by the EULAR/ACR criteria in almost 30% of patients. We suggest incorporating anti–MDA-5 antibody positivity as a criterion into existing criteria sets or developing specific criteria for patients with anti–MDA-5–positive IIM.