Bohan and Peter is the oldest criteria for the classification of idiopathic inflammatory myopathies (IIM). Recently, 2017 EULAR/ACR criteria were introduced which were validated against a control group. The objective of this study was to assess the performance of the 2017 EULAR/ACR criteria in retrospective cohort of adult and juvenile idiopathic inflammatory myopathies and compare with Bohan and Peter criteria. This was a retrospective study of patients clinically diagnosed to have IIM in a tertiary care center in the last 10 years. Only patients with a minimum follow-up of 6 months and response to steroids and immunosuppression were included in the study. Performance of both the criteria in the cohort was assessed and compared with clinical diagnosis. Hundred and eleven patients (87 females) were included in the study. Eleven patients had juvenile onset. Ninety-three patients (83.8%) were classified as probable/definite myositis using the Bohan and Peter criteria. Eighty-nine (80.2%) patients were classified as having probable/definite inflammatory myositis using the new criteria. Agreement between the two criteria was weak in our cohort (κ-0.331). Complete details of muscle biopsy were available in 52 patients. In this subgroup, 96% were classified by Bohan and Peter and 80.8% by EULAR/ACR criteria. Bohan and Peter classified 73% and EULAR/ACR 82% of patients when biopsy was excluded (n = 111). Both criteria classified over 90% of the patients with dermatomyositis. Forty-two patients were clinically diagnosed as polymyositis, of these 32 patients had myositis overlap syndrome. Bohan and Peter classified 66.7% and EULAR/ACR classified 64.3% in this subset. Bohan and Peter criteria had high sensitivity in the presence of muscle biopsy compared with EULAR/ACR. The performance of the EULAR/ACR criteria was similar to Bohan and Peter in the absence of muscle biopsy. Both criteria had poor sensitivity in polymyositis.
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