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

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.