While the revised European Alliance of Associations for Rheumatology/American College of Cardiology (EULAR/ACR) classification criteria has seemingly outperformed the traditional Bohan/Peter criteria, EULAR/ACR criteria failed to classify nearly 30% of study patients with antimelanoma differentiation-associated protein 5 (MDA5)-associated idiopathic inflammatory myopathy (IIM), according to study results published in Arthritis & Rheumatology.

The multicenter, retrospective study was conducted in 10 hospitals in Hong Kong. Patients’ clinical characteristics were obtained via review of electronic medical records. Myositis-specific antibodies (MSA) were detected with use of commercial line-blot immunoassays. Incorporation of the anti-MDA5 antibody in the EULAR/ACR criteria and the MSA-based criteria were assessed, as well. Use of a new set of phenotypic-serologic classification was proposed by the research group.

A total of 120 patients with anti-MDA5-associated IIM were recruited for the study; 55.0% of the patients were women. Patient subgroups included those with dermatomyositis (DM; 31.7% of study patients) and those with clinical amyopathic dermatomyositis (CADM; 68.3% of study patients). Overall, 86 patients met the EULAR/ACR classification criteria (71.7%) and 49 patients met the Bohan/Peter criteria (40.8%).


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The mean follow-up duration among the study participants was 19.4±21.6 months. The mean participant age at diagnosis was 52.7±21.6 months (range, 21-88 years). In total, 117 of the study patients were Chinese (97.5%). Thirty-eight patients had DM (31.7%) and 82 patients had CADM (68.3%). Mean time from onset of symptoms to disease diagnosis was 85.9±75.1 days. Among all study patients, 104 had interstitial lung disease (ILD; 86.7%) and 49 developed rapidly progressive ILD (40.8%).

When the Sontheimer criteria for CADM were added, 76.7% of the patients could be classified by the Bohan/Peter criteria. If anti-MDA5 antibody was considered as one of the criterion, then the sensitivity of the EULAR/ACR criteria could be improved to 98.3%. The criteria of Casal-Dominguez et al. demonstrated 100% sensitivity in the patient cohort being evaluated. This newly-proposed criteria for “anti-MDA5 syndrome” could classify 97.5% of the study patients.

A major limitation of the study was the fact that despite its increasing popularity, the line-blot immunoassay had not yet been fully validated. Selection bias might also exist. Because of the retrospective design of the study, incomplete data collection was unavoidable.

The study authors concluded that incorporation of anti-MDA5 antibody into the EULAR/ACR criteria via use of a generic MSA-based classification or adoption of a specific phenotypic-serologic “anti-MDA5 syndrome” approach greatly improved the ability to classify individuals with anti–MDA5-associated IIM.

Reference

So H, So J, Lam TT, et al. Performance of the 2017 EULAR/ACR classification criteria in anti-MDA5 associated idiopathic inflammatory myopathy. Arthritis Rheumatol. Published online April 25, 2022. doi:10.1002/art.42150