Evaluation of Autoimmune Features in Patients with Idiopathic Pulmonary Fibrosis and Pathologic Usual Interstitial Pneumonia: Implications for CT Patterns and Prognosis

Background The clinical, radiologic, and prognostic implications of interstitial pneumonia with autoimmune features (IPAF) in patients with idiopathic interstitial pneumonia and pathologic usual interstitial pneumonia (UIP) have not been fully evaluated. Purpose To compare autoimmune features according to CT patterns for the diagnosis of idiopathic pulmonary fibrosis (IPF) and to assess the diagnostic and prognostic implications of IPAF in patients with IPF-UIP. Materials and Methods This retrospective study included patients with UIP confirmed by surgical lung biopsy between January 2013 and February 2020. Data regarding clinical, radiologic, and pathologic autoimmune features were collected, and patients were diagnosed with IPAF according to current guidelines. CT signs for connective tissue disease (CTD; anterior upper lobe, straightedge, and exuberant honeycombing signs) were also evaluated. Overall survival (OS) was evaluated using Cox proportional hazards models. Results Among 210 patients included (median age, 64 years; IQR, 60-68 years; 158 male patients), 23 (11.0%) had IPAF. Patients with an alternative diagnosis or CT pattern indeterminate for UIP showed a higher prevalence of autoimmune features that were pathologic (38% [33 of 87] vs 20.3% [25 of 123]; P = .005) and serologic (20% [17 of 87] vs 9.8% [12 of 123]; P = .04) and IPAF (4.1% [five of 123] vs 21% [18 of 87]; P < .001) compared with patients with UIP or probable UIP pattern. However, IPAF was not predictive of OS (hazard ratio [HR], 0.81; 95% CI: 0.38, 1.72; P = .58). Lymphoid follicles (HR, 0.59; 95% CI: 0.37, 0.93; P = .02), CT signs for CTD (HR, 0.31; 95% CI: 0.09, 0.99; P = .047), and use of an antifibrotic agent (HR, 0.31; 95% CI: 0.19, 0.51; P < .001) were independently associated with higher OS, and greater extent of fibrosis on CT scans was associated with worse OS (HR, 1.08; 95% CI: 1.05, 1.11; P < .001). Conclusion In patients with IPF-pathologic UIP, serologic and pathologic autoimmune features were associated with indeterminate or alternative CT patterns. Certain histopathologic and radiologic autoimmune features, but not current IPAF criteria, were associated with survival. © RSNA, 2025 Supplemental material is available for this article. See also the editorial by Ackman in this issue.