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Comment & Response
April 1, 2019

Autoantibodies at the Center of (sub)Classification—Issues of Detection

Author Affiliations
  • 1Skeletal Biology and Engineering Research Center, Department of Development and Regeneration, KU Leuven, Leuven, Belgium
  • 2Department of Rheumatology, University Hospitals Leuven, Leuven, Belgium
  • 3Inova Diagnostics, San Diego, California
JAMA Neurol. 2019;76(7):867-868. doi:10.1001/jamaneurol.2019.0440

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