Clinical profiles and lung function trajectories of IIM-ILD patients: A comparative study of pulmonology and rheumatology settings.

Abstract

Idiopathic inflammatory myopathies (IIM) are frequently complicated by interstitial lung disease (ILD). Although clinical heterogeneity is recognized, comparisons between IIM-ILD patients managed in pulmonology- versus rheumatology centers remain limited. Do differences in clinical features, treatment strategies, lung function trajectories, and transplant-free survival among IIM-ILD patients followed at pulmonology or rheumatology centers exist? We conducted a multicenter observational cohort study including 75 IIM-ILD patients diagnosed between 2014 and 2024: 25 from two Italian pulmonology centers and 50 from a rheumatology center in Norway. All met IIM classification criteria, had ILD confirmed by high resolution computed tomography (HRCT), and serial pulmonary function tests. Associations of baseline features, imaging patterns, and treatments with referral center were assessed using logistic regression. Lung function trajectories were assessed with linear mixed-effects models, and transplant-free survival with Cox regression. Pulmonology patients were more often male, had more fibrotic ILD (OR 5.61, 95% CI 1.88-16.73, p=0.002), with lower baseline DLCO (OR 0.96, 95% CI 0.93-0.99, p=0.048), less cutaneous (OR 0.11, 95% CI 0.03-0.40, p=0.001) and musculoskeletal involvement and rituximab was less used (OR 0.06, 95% CI 0.01-0.23, p<0.001) compared to rheumatology patients. Despite baseline differences, both cohorts showed significant and comparable improvement in FVC and DLCO% predicted over mean 2.5 years. Transplant-free survival did not differ significantly between specialty centers. Factors associated with worse transplant-free survival included anti-MDA5 positivity (HR 10.24, 95% CI 1.70-61.66, p=0.011), elevated CRP, and extensive lung fibrosis. While baseline presentation and treatment characteristics of IIM-ILD patients differed between rheumatology and pulmonology cohorts, transplant-free survival was comparable. Including patients from both pulmonology and rheumatology in future clinical trials may enhance representativeness without compromising data consistency.