Distinctive characteristics and prognostic significance of interstitial pneumonia with autoimmune features in patients with chronic fibrosing interstitial pneumonia.

Background: Interstitial lung diseases are heterogeneous, and patients with chronic fibrosing interstitial pneumonia (CFIP) often have clinical, serologic, and morphologic features suggestive but not diagnostic of connective tissue disease. Recently, the concept of interstitial pneumonia with autoimmune features (IPAF) has been proposed as a platform for such patients. However, the prognostic role of IPAF, including the cumulative incidence of acute exacerbations (AEs), is not fully clear. The aim of this study was to elucidate the clinical features and prognostic significance of IPAF.

Methods: The clinical characteristics and prognostic relevance of a diagnosis of IPAF were retrospectively explored in 194 patients with CFIP, including 163 with idiopathic pulmonary fibrosis (IPF) and 31 with nonspecific interstitial pneumonia (NSIP), in our interstitial lung disease database.

Results: Sixteen percent of patients with CFIP (8% of IPF, 61% of NSIP) met the criteria for IPAF. Patients with IPAF were significantly younger and included a higher proportion of women, never-smokers, and patients with NSIP than those without IPAF. The morphologic domain was the most common in patients with IPAF (97%), followed by the serologic domain (72%) and clinical domain (53%). CFIP patients with IPAF had a more favorable prognosis with regard to overall survival (OS; P < 0.001, log-rank test) and incidence of AEs (P = 0.029, Gray's test) than those without IPAF. In the subgroup analysis, NSIP patients with IPAF had significantly better survival than those without IPAF (P = 0.031, log-rank test), and IPF patients with IPAF tended to have better OS than those without IPAF (P = 0.092, log-rank test). However, there were no significant differences in the incidence of AEs between patients with IPAF and those without IPAF in the IPF and NSIP subgroups. Furthermore, fulfilment of the IPAF criteria was an independent predictor of OS (hazard ratio (HR) 0.127; 95% confidence interval (CI) 0.017-0.952; P = 0.045) and incidence of AEs (HR 0.225: 95% CI 0.054-0.937; P = 0.040).

Conclusions: A diagnosis of IPAF might predict a favorable prognosis and less risk of AEs in patients with CFIP.