External validation of the 2017 EULAR/ACR classification criteria for idiopathic inflammatory myopathies in anti-MDA5 antibody-positive interstitial lung disease patients: A multicenter retrospective cohort study in China.

Unlabelled: The aim of this study was to assess the 2017 EULAR/ACR classification criteria performance for determining idiopathic inflammatory myopathies (IIMs) in a cohort of patients with anti-MDA5 antibody-positive IIM-related interstitial lung disease (anti-MDA5+IIM-ILD). The outcomes of patients, who did not meet the EULAR/ACR criteria, and who had interstitial pneumonia and exhibited an autoimmune phenotype associated with anti-MDA5 positivity were also investigated.

Methods: This retrospective study recruited adult patients from four hospitals in China who were diagnosed with anti-MDA5 antibody-positive IIM-related interstitial lung disease. Data on disease manifestations, laboratory findings, and imaging findings were collected through electronic medical records. The performance and consistency of the 2017 EULAR/ACR classification criteria were compared with those of the Bohan/Peter criteria combined with Sontheimer's CADM criteria. Additionally, this study evaluated the performance of incorporating anti-MDA5 antibodies into the EULAR/ACR criteria and explored the criteria proposed by Casal-Domingez based on myositis-specific antibodies (MSAs). Finally, clinical characteristics and prognoses were compared between patients with MDA5+IIM-ILD who met the EULAR/ACR criteria and those who did not meet the EULAR/ACR criteria.

Results: A total of 250 patients with anti-MDA5-related IIM-ILD, including those with dermatomyositis (DM, 23.6 %) and clinically amyopathic dermatomyositis (CADM, 76.4 %), were recruited. Of these, 175 (70 %) and 64 (25.7 %) patients met the EULAR/ACR and Bohan/Peter criteria, respectively. According to Sontheimer's CADM criteria, 60.4 % of patients could be classified according to the Bohan and Peter criteria. Thirty percent of the anti-MDA5 antibody-positive patients did not meet the EULAR/ACR criteria but met the IPAF criteria. The sensitivity of the EULAR/ACR criteria increased to 99.2 % when anti-JO-1 antibodies were replaced with anti-MDA5 antibodies. In this cohort, a sensitivity of 100 % was obtained using the Casal-Domingez criteria. There were no significant differences in clinical characteristics or prognoses between MDA5+IIM-ILD patients who met the EULAR/ACR criteria, those who did not meet the criteria, and those who met the IPAF criteria.

Conclusion: Approximately 30 % of clinically diagnosed anti-MDA5 antibody-positive IIM-ILD patients cannot be classified according to the EULAR/ACR criteria, suggesting that such patients should be managed as IIM-ILD patients. Modifying the existing criteria by including other MSAs, such as anti-MDA5 antibodies, as one of the scoring criteria is recommended. Future IIM guidelines should consider incorporating ILD into the diagnostic criteria.