Clinical Characteristics and Evolution of Interstitial Lung Disease in Subtypes of Idiopathic Inflammatory Myositis With Prevalent Lung Manifestation: A Retrospective Analysis

OBJECTIVE: Interstitial lung disease (ILD) is common in idiopathic inflammatory myositis (IIM), particularly in antisynthetase syndrome (ASyS), antimelanoma differentiation-associated protein 5 (anti-MDA5) syndrome, and scleromyositis. ILD can progress despite resolution of extrapulmonary symptoms, termed postmyopathic progressive pulmonary fibrosis (PmPPF). We outlined ILD trajectories in these subgroups of IIM, focusing on PmPPF. METHODS: A retrospective review of patients with IIM (ASyS, anti-MDA5+ dermatomyositis [DM], scleromyositis) from a British Columbia cohort (2019-2024) assessed demographics, auto-antibodies, treatments, and ILD progression. RESULTS: Among 111 patients with ASyS, anti-MDA5+ DM, and scleromyositis (median age 51 years, follow-up 35.5 months), ILD prevalence was highest in ASyS (87.5%), followed by anti-MDA5+ DM (84.6%), and scleromyositis (65.5%). PmPPF occurred in 13.5% of the cohort, predominantly in anti-MDA5+ DM (23.1%) and ASyS (16.1%) but not in scleromyositis. Patients with PmPPF had higher rates of active disease (46.7% vs 9.3%), rapidly progressive ILD (33.3% vs 5.3%), and lung transplantation (20% vs 1.3%). Anti-MDA5+ DM exhibited the highest remission rate (88.5%) but also the highest transplant requirement (11.5%). Organizing pneumonia (OP)/nonspecific interstitial pneumonia (NSIP) overlap on high-resolution computed tomography was more common in PmPPF (33.3% vs 9.3%). PmPPF showed a nonsignificant trend toward higher mortality compared to non-PmPPF (20% vs 4%). Rituximab use was greater in PmPPF (73.3% vs 37.3%). CONCLUSION: This study highlights distinct ILD patterns across three idiopathic inflammatory myopathy subtypes, with PmPPF occurring more frequently in ASyS and anti-MDA5+ DM but not in scleromyositis. The persistence of ILD progression independent of extrapulmonary disease activity underscores the importance of ongoing pulmonary monitoring and multidisciplinary management.