Background/Purpose: Limitations of the 2017 EULAR/ACR classification criteria have been suggested for classifying patients with idiopathic inflammatory myopathies (IIMs) and myositis-specific antibodies (MSAs). On this point, Casal-Dominguez et al recently developed a set of MSAs-based classification criteria that demonstrated perfect sensitivity and specificity (1).

The objective of this study was to determine whether the EULAR/ACR classification criteria and the MSAs-based classification criteria appropriately classify patients with IIMs, differentiating between incident and prevalent cases

Methods: Multicenter cross-sectional study of a cohort of patients included in the Spanish Registry of patients with IIM (Myo-Spain) (2). Patients were classified as incident group (time between diagnosis and study initiation ≤12 months) or prevalent group ( >12 months). The accuracy of the classification criteria according of the presence of different MSAs was described. Differences between both groups were tested by Chi-square test. The sensitivity and specificity of the MSAs-based classification criteria was determined. The percent of agreement and the Cohen’s Kappa coefficient was used to measured correlations between the EULAR/ACR criteria and the MSAs-based criteria

Results: We included 542 patients with IIM diagnosis, 132 (24.4%) and 410 (75.6%) patients in the incident and prevalent group, respectively. In the overall sample, the diagnosis could be classified with the EULAR/ACR criteria in 284 patients (52.4%) and with the MSAs-based criteria in 344 patients (99.4%). Differentiating by MSAs type, patients were successfully classified by EULAR/ACR criteria as follows: 57.6 % of anti-Jo1-positive patients; 49.3% of MSAs-positive myositis patients (except anti-Jo1 antibody); 52.3% of MSAs-positive myositis patients; 52.5% of patients without MSAs antibodies (table 1). No significant differences were found between the two groups (p >0,05). Regarding MSAs-based classification criteria, patients were successfully classified as follows: 92.1% of anti-synthetase-positive patients and 100% of MSAs-positive (except anti-synthetase antibody) patients (table 2). No significant differences were found between the two groups (p >0,05).The sensitivity and specificity of the MSAs-based criteria were 100% in the incident group and 99.2% and 100%, respectively, in the prevalent group. The percentage of agreement between the EULAR/ACR criteria and the MSAs-based criteria for IIMs was 49.2% in the incident group and 50.9% in the prevalent group. This value was 48.1% and 60.2% in anti-Jo1-positive subgroup (Cohen’s Kappa=0).

Conclusion: The degree of accuracy of the EULAR/ACR criteria for classifying patients with IIM diagnosis was lo, however, the MSAs-based criteria showed excellent diagnostic accuracy. No agreement was found between both classification criteria. Therefore, it seems necessary to review the classification criteria for MII, in which, in addition to including all MSAs, the difficulty in classifying patients without MSAs should be considered.

(1) Casal-Dominguez M et al. Arthritis Rheumatol 2022. (2) Cobo-Ibáñez T et al. Reumatol Clin. 2022.

« Back to ACR Convergence 2023

ACR Meeting Abstracts - https://acrabstracts.org/abstract/accuracy-of-the-2017-european-alliance-of-associations-for-rheumatology-eular-american-college-of-rheumatology-acr-classification-criteria-and-myositis-specific-autoantibodies-based-classification/