Observational longitudinal study to assess the outcome of patients with idiopathic inflammatory myositis using validated tools

Abstract Introduction There have been major changes in the classification and treatment of patients with idiopathic inflammatory myositis (IIM) in the last 2 decades. A major challenge is to identify the parameters that can affect the outcome and prognosis of these patients. Here, we have longitudinally followed a well‐characterized cohort of IIM patients in a rheumatology center and reported the outcome using the validated tools. Method Patients with a clinical diagnosis of IIM and a follow‐up duration of greater than 2 years were prospectively included in the study. The duration of the study was 6 years: July 2016–July 2022. Clinical details and follow‐up were recorded using pro‐formas and outcomes were noted using validated tools. Ethics approval and written informed consent were taken. Results Forty patients had a clinical diagnosis of IIM. Mean follow‐up duration was 43.8 (15) months. Out of 40 patients, 32 (80%) achieved remission (8 patients each were off corticosteroid and off treatment for >6 months), 5 (12%) expired and 3 (8%) had active disease. Disease course was non‐relapsing in 22/35 (73%) patients. Mean manual muscle testing‐8 score ( n = 29) and myositis disease activity assessment tool score ( n = 35) at the final visit were 75.6 (6.8) and 0.048 (0.07) respectively. Thirteen patients had damage (37%). Patients with disease duration >1 year at the time of presentation were more likely to develop chronic‐continuous disease course ( P = .023, odds ratio [OR] = 7.6), more frequently required second‐line or third‐line immunosuppression ( P = .001, OR = 24) with higher myositis damage index score ( p = .0002, OR = 47). Conclusions IIM patients had good outcomes with the majority achieving remission and near‐complete muscle recovery. However, the patients presenting late to the rheumatologists were more likely to have smoldering disease, more immunosuppressive medicines, and greater accumulated damage.