Patients with idiopathic inflammatory myopathies (IIM), including dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM), and juvenile idiopathic myositis, show heterogeneous clinical symptoms that reflect differences in organ involvement, but all of these conditions include muscle weakness [1]. Among rheumatic diseases, the diagnosis of IIM can be complicated and both clinicians and investigators have struggled to define a homogeneous group of clinical, laboratory and pathologic features that can be used to separate IIM from other conditions, thus facilitating treatment and providing a detailed focus for clinical research. Most classification criteria are based on accumulated clinical and laboratory manifestations that appear with high certainty in patients who have developed or been diagnosed with a specific disease [2-4]. Among major proposed classification criteria for the different forms of IIM, the comprehensive Bohan and Peter [2] criteria for PM and DM have been used extensively in the clinical setting during the last four decades. The criteria distinguish definite from possible PM and DM based on an initial assessment of “characteristic rashes” to distinguish DM and then offers more detailed descriptions for five subgroups of PM/DM, including juvenile, overlapping, and cancer-associated forms of myositis. The modification of the Bohan and Peter criteria proposed by Dalakas added criteria for IBM and identified important muscle biopsy features that led to major advances in practice and in clinical trials [3]. Potential markers associated with distinct clinical phenotypes, such as myositis-specific autoantibodies (MSA), can provide important insights but they have not yet been validated for use in the establishment of diagnostic criteria [4]. In 2017, the European League Against Rheumatism/American College of Rheumatology developed classification criteria (2017 EULAR/ACR criteria) for adult and juvenile IIM that were validated in a data-driven analysis of children and adults with different ethnicities who were seen at centers in Europe, America, and Asia [5]. The major subgroups recognized by these criteria were developed through an international multidisciplinary collaboration, the International Myositis Classification Criteria Project (IMCCP) [6]. The 2017 EULAR/ACR criteria employ a scoring system in which a score < 5.3 is used to rule out IIM (non-IIM) [5]. A remarkable difference from previous criteria was the addition of dysphagia and anti-Jo-1 positivity [5,6]. Patients with pathognomonic skin rashes (heliotrope rash, Gottron’s papules and/or Gottron’s sign) are considered to have juvenile DM or DM without muscle biopsy findings (Fig. 1) [5]. Nevertheless, the Bohan and Peter criteria are still commonly used to classify IIM due to their reliance on a small number of variables and their convenient application in routine clinical settings [7].