Prognostic and Functional Trajectories in Idiopathic Pulmonary Fibrosis and Systemic Autoimmune Rheumatic Disease–Associated Interstitial Lung Disease: Insights From an Italian Multicenter Cohort

Objective Idiopathic pulmonary fibrosis (IPF) and systemic autoimmune rheumatic disease (SARD)-associated interstitial lung disease (ILD) are lung disorders with distinct clinical trajectories. This study aimed to compare survival and pulmonary function trends between IPF and SARD-ILD. Methods We retrospectively analyzed 410 patients with ILD (154 IPF, 256 SARD-ILD) from 6 Italian centers. SARD-ILD subtypes included antisynthetase syndrome (ASyS; n = 58), dermatomyositis (DM; n = 55), systemic sclerosis (SSc; n = 106), and Sjögren disease (SjD, n = 37). Outcomes included 5-year survival and pulmonary function test (PFT) changes. Results Five-year survival was lower in patients with IPF (mean 33.6 months) than in those with SARD-ILD (mean 56.0 months; P < 0.001). SARD subtypes showed comparable survival: 58.2 months in patients with ASyS, 52.9 months in DM, 55.2 months in SSc, and 58.6 months in SjD. Patients with ASyS and DM demonstrated significant functional improvement, with forced vital capacity (FVC) increasing from 71% to 81% in ASyS (+14.1% relative) and from 69% to 78% in DM (+13%). IPF FVC declined from 78% to 72% (−7.7%). Usual interstitial pneumonia pattern was universal in IPF but seen in < 20% of patients with SARD-ILD. ILD pattern did not significantly influence functional trajectory in patients with SARD-ILD; instead, diagnosis was the primary determinant (multivariable ANOVA P < 0.001). Multivariable analysis confirmed SARD-ILD as a favorable prognostic factor (adjusted hazard ratio [aHR] 0.21), with age (aHR 1.06) and male sex (aHR 1.98) linked to poorer outcomes. Conclusion SARD-ILD is associated with higher survival than IPF. Functional trajectories improved in patients with ASyS and DM, in contrast to the decline observed in those with IPF. Prognosis is more strongly influenced by the underlying diagnosis, supporting a diagnosis-centered approach to disease management.