To the Editor It was with interest that we read the article by Mariampillai et al1 describing a new classification approach for idiopathic inflammatory myopathies (IIM) based on clinical manifestations and myositis-specific autoantibodies (MSAs).1 The authors describe their classification system as complementary to the recently published European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria, as they focus on defining IIM subsets (clusters) rather than IIM diagnoses. The EULAR/ACR criteria attempted to subgroup as well, but an immune-mediated necrotizing myopathy (IMNM) subgroup could not be isolated, which is worrisome given the clinical consensus on its status as a subgroup and inclusion in previous classification approaches.2,3 The 4 clusters proposed by Mariampillai et al were significantly associated with some MSAs (eg, anti–3-hydroxy-3-methyl-glutaryl-coenzyme A reductase and cluster 2, corresponding to IMNM). This is reflected in the major role of MSAs in allocating patients to a specific cluster in their decision tree. In the EULAR/ACR criteria, only the presence of anti–Jo-1 was included as a classification criterion, generating debate on the role of MSAs in the classification of IIMs.2,4
Vulsteke J, De Langhe E, Mahler M. Autoantibodies at the Center of (sub)Classification—Issues of Detection. JAMA Neurol. 2019;76(7):867–868. doi:https://doi.org/10.1001/jamaneurol.2019.0440
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