Reclassification of Korean patients with polymyositis and dermatomyositis based on the Bohan and Peter criteria by the 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies

BACKGROUND/AIMS: We investigated the concordance rate of the classification of polymyositis (PM) and dermatomyositis (DM) between the Bohan and Peter criteria and the 2017 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria for idiopathic inflammatory myopathies (IIMs) (the 2017 EULAR/ACR criteria) in Korean patients. METHODS: We retrospectively reviewed the medical records of 137 patients with PM and DM. We finally included 72 PM patients and 49 DM patients who fulfilled the Bohan and Peter criteria for PM and DM and reclassified them by the 2017 EULAR/ ACR criteria. RESULTS: Three patients (4.2%) with probable PM were newly reclassified as non-IIM due to a total score of 5.3 or smaller. Meanwhile, one patient with possible PM was newly reclassified as probable PM due to the presence of dysphagia. In addition, eight patients (16.3%) with possible DM with DM-specific typical skin rash were newly reclassified as amyopathic DM (ADM) due to the absence of proximal muscle weakness. The concordance rate of the classification between the Bohan and Peter criteria and the 2017 EULAR/ACR criteria was 95.8% for PM patients and 83.7% for DM patients. CONCLUSIONS: The Bohan and Peter criteria were comparable to the 2017 EULAR/ ACR criteria for classifying PM and DM in Korean patients. Considering the convenience of the Bohan and Peter criteria in the real clinical settings, we suggest that the old criteria should be preferentially applied and then performing muscle biopsy should be considered in a patient suspected of PM without antihistidyl tRNA synthetase (anti-Jo-1). Moreover, we suggest that ADM could also clinically be classified by the old criteria.