B41-48 Incidence, Clinical Features, and Prognosis of Interstitial Pneumonia With Autoimmune Features (IPAF) in Patients With Newly Diagnosed ILD: A Retrospective Single-Center Study

Background Interstitial pneumonia with autoimmune features (IPAF) has been proposed to characterize patients with interstitial lung disease (ILD) who exhibit autoimmune manifestations but do not meet the criteria for a connective tissue disease. In this study, we aimed to determine the prevalence, clinical characteristics, and prognosis of IPAF at the time of ILD diagnosis. Methods We conducted a retrospective analysis of patients who were diagnosed with ILD between 2018 and 2022 at a single center in Korea. IPAF was defined according to the 2015 ERS/ATS criteria, and rheumatologists independently confirmed the classification. Disease progression was defined as an absolute decline of more than 10% in forced vital capacity or more than 15% in diffusing capacity of the lung for carbon monoxide (DLco) in 2 years. Results Of 769 subjects, the median age was 69.2 years, and 66.2% were male. 10.7% met the criteria of IPAF at initial diagnosis, and IPF was the most common (44.2%), followed by other ILD (36.6%), and connective tissue disease-associated ILD (CTD-ILD). IPAF patients tended to be younger and more often female, with a lower prevalence of smoking history. During the follow-up period, 17 patients (20.7%) with IPAF were subsequently reclassified as CTD-ILD. About half of the patients with IPAF (52.2%) showed disease progression, a higher proportion than in CTD-ILD. In the multivariable COX proportional hazard regression analysis, a higher count of white blood cells (WBC) was the only significant risk factor for progression (HR 1.22, 95% CI: 1.10-1.36, p < 0.001). A total of 15.4% of patients with IPAF died during follow-up, indicating a better survival (Log rank test, p < 0.001) compared with those with IPF (22.9%) but worse than that of patients with other ILD (7.8%). The multivariable COX analysis revealed that lower DLco (HR 0.90, 95% CI: 0.83-0.97, p = 0.007) and a higher count of white blood cells (HR 1.40, 95% CI: 1.08-1.92, p = 0.011) were independent risk factors for mortality. Conclusion At the time of ILD diagnosis, 10.7% of patients were classified with IPAF and showed a high rate of developing CTD. Disease progression was more frequent in IPAF than in CTD-ILD, while survival was better than in IPF but poorer than in other ILD. This abstract is funded by: None