[What the New International Classification Criteria for Idiopathic Inflammatory Myopathy Tell Us].

The classification criteria of idiopathic inflammatory myopathy in the past include the criteria defined phenotypically by Peter and Bohan in 1975 and the criteria defined based on pathological findings in affected muscles. New criteria were defined by international researchers, including the author of this article, from multiple fields to be used widely in different fields in 2017. The criteria were approved by rheumatological societies in Europe and the United States, and validated as excellent criteria in a Japanese cohort. It is known that the criteria used for etiological studies and those for diagnosis should be different in their stringency. In the new criteria, the stringency can be set freely by the users to be used for a wide range of purposes.