Factors Associated With Treatment Response in Patients With Idiopathic Inflammatory Myopathies: A Registry‐Based Study

OBJECTIVE: To identify predictors of response to immunosuppressive therapy after 1 year, with a focus on autoantibodies, in patients newly diagnosed with idiopathic inflammatory myopathies (IIM) followed longitudinally in an electronic registry. METHODS: We assessed the association between autoantibody‐defined groups and improvement according to American College of Rheumatology/European Alliance of Associations for Rheumatology 2016 response criteria. RESULTS: We identified 156 patients; of those, 111 (71%) were positive for any autoantibody tested, 90% received glucocorticoid treatment at baseline, and 78% received immunosuppressive drugs at some follow‐up point. After 1 year from the index date, the overall median improvement score was 27.5 (interquartile range 10–51). No differences were observed in the total improvement score between the autoantibody‐defined groups. Overall, 62% of patients (n = 96) showed a minimal response, 38% (n = 60) achieved a moderate response, and 19% (n = 30) achieved a major response. Regarding the different levels of response, dermatomyositis‐specific autoantibodies were associated with a moderate response versus the seronegative group (reference), odds ratio 4.12 (95% confidence interval 1.2–16.5). In addition, dysphagia, time from symptom onset to diagnosis, and initial glucocorticoid dose were significant predictors of response after 1 year of follow‐up. CONCLUSION: Patients with DM‐specific autoantibodies achieved better levels of response compared to other autoantibody‐defined groups. Dysphagia, a shorter time span from symptom onset to diagnosis, and intensive initial immunosuppressive treatment were associated with a higher response rate after 1 year of pharmacologic treatment from the index date, regardless of autoantibody status.