Background and Aim: Progressive pulmonary fibrosis (PPF) is a clinically significant phenotype observed across fibrotic interstitial lung diseases (ILDs), characterized by pulmonary functional decline, radiologic progression, and worsening symptoms. While declines in forced vital capacity (FVC) and diffusing capacity for carbon monoxide (DLCO) are widely used to define progression, the prognostic value of baseline radiologic fibrosis burden in real-world PPF cohorts remains incompletely defined. We aimed to evaluate the relationships among HRCT-derived fibrosis extent, pulmonary function decline, and overall survival in patients with PPF.

Methods: In this retrospective single-center study, 99 patients with progressive fibrotic ILD who were followed between 2010 and 2019 were included. PPF was defined according to accepted criteria, including functional, radiologic, and symptomatic progression. The extent of fibrosis on HRCT was assessed by two independent radiologists using a semi-quantitative visual scoring method. Cox regression models were used to identify predictors of mortality.

Results: Baseline HRCT fibrosis extent was independently associated with mortality. In a multivariable analysis adjusted for age, sex, smoking status, and diagnosis, each 1% increase in fibrotic involvement was associated with a 4.7% higher risk of death (HR 1.050, 95% CI 1.025–1.076; p<0.001). In contrast, categorical declines in FVC or DLCO (≥5% or ≥10%) were not independently associated with survival. Baseline DLCO impairment and smoking history were also associated with reduced survival.

Conclusion: In patients with PPF, radiological fibrosis burden on HRCT outperformed conventional spirometric decline thresholds in predicting mortality. These findings support an integrated prognostic approach combining standardized HRCT quantification with longitudinal functional assessment to improve risk stratification and clinical decision-making in PPF.