Applicability of EULAR/ACR classification criteria for dermatomyositis to amyopathic disease

Background Existing classification systems for idiopathic inflammatory myopathies (IIMs) fail to permit classification and/or diagnosis of amyopathic dermatomyositis (ADM) in patients. Objective In light of the new European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for IIM, we evaluated the likelihood of the skin variables included in the EULAR/ACR criteria (Gottron's sign, Gottron's papules, and heliotrope rash) to give a high probability of classifying patients with ADM. Methods This retrospective study evaluated 211 adult patients with dermatomyositis at the University of Pennsylvania. The EULAR/ACR criteria were used to determine the probability of classification for patients with ADM. Results Of patients with ADM, 73.7% would be classified as having a reasonable probability of dermatomyositis on the new EULAR/ACR criteria and 26.3% would not meet the suggested 55% minimum probability cutoff to be classified as having it on the basis of the EULAR/ACR criteria. Limitations This study was conducted with a retrospective design at a tertiary academic medical center. Conclusions The 3 skin variables included in the EULAR/ACR classification criteria for IIM improve on previous criteria but miss classifying some patients with ADM. It is important to consider additional variables such as skin biopsy results to encompass more of these patients and prevent the inclusion of any skin diseases mimicking ADM.