Background Progressive pulmonary fibrosis (PPF) represents a common disease behaviour across fibrotic interstitial lung diseases (F-ILDs). PPF was defined in 2022, but data on extent and prognosis remain limited. The aim of this study was to determine the proportion who progress to PPF, investigate predictors of PPF and compare survival between PPF- and non-PPF patients. Methods This prospective longitudinal cohort study included all incident cases of F-ILD diagnosed at Danish tertiary ILD centres between 1 June 2016 and 31 May 2017. Patients with idiopathic pulmonary fibrosis or fewer than two pulmonary function tests were excluded. Data were obtained from the Danish ILD database (DANILDA) and national registries. PPF was defined according to the 2022 criteria. Survival was analysed using Kaplan–Meier estimates and Cox regression with PPF modelled as a time-dependent covariate and delayed entry handled by left truncation. Results Among the 197 patients included, 57% developed PPF during four years of follow-up (median 13 months). No baseline variables predicted PPF development. The PPF group experienced a greater annual decline in FVC (adjusted mean difference −140 mL/year, p=0.001) and DLCO (−2.97 percentage points/year, p=0.009) than the non-PPF group. Three-, five-, and seven-year survival rates were 73%, 58%, and 48% in PPF, and did not differ significantly between PPF and non-PPF. A higher baseline ILD-GAP stage was independently associated with decreased survival (HR 2.64, p<0.001). Conclusion In this nationwide real-world cohort, almost six of ten patients with F-ILD developed PPF within four years. Although patients with PPF exhibited a greater annual decline in FVC, survival did not differ between PPF and non-PPF.
Kølner-Augustson et al. (Thu,) studied this question.