Associations of interstitial lung disease subtype and CT pattern with lung function and survival.

Background: Prior work suggests different interstitial lung diseases (ILDs) that share the radiological usual interstitial pneumonia (UIP) pattern have an overall worse prognosis. However, epidemiological data with longitudinal sampling and replication remains lacking.

Methods: Data was used from the Pulmonary Fibrosis Foundation Patient Registry (PFF-PR) (n=932) and a meta-cohort of ILD research studies (n=1579). Linear mixed-effects models and Cox proportional hazard models were used to determine forced vital capacity (FVC) slopes and 5-year transplant-free survival, respectively, by ILD diagnosis and UIP radiological pattern. Secondarily, we examined FVC and survival by diagnosis and radiological fibrosis quantified by data-driven texture analysis (DTA) in the PFF-PR. Models were adjusted for age, sex, smoking and antifibrotic and immunosuppression medication use.

Results: The proportions of idiopathic pulmonary fibrosis (IPF), fibrotic hypersensitivity pneumonitis (FHP) and connective tissue disease (CTD)-ILD were the following for PFF-PR (70%, 11%, 19%) and meta-cohort (21%, 32%, 47%). In the PFF-PR, CTD-ILD with UIP CT pattern was associated with slower FVC decline (-34.4 mL/year) compared with IPF (-158.4 mL/year) and longer transplant-free survival (HR 0.50, 95% CI 0.29 to 0.85). This was replicated in the meta cohort for FVC (-53.1 vs -185.9 mL/year, p<0.0001) and survival (HR 0.38, 95% CI 0.27 to 0.53). A similar pattern was seen using DTA to objectively categorise patients into higher and lower radiological fibrosis. Between IPF and FHP-UIP, FVC decline was not significantly different in the PFF-PR (-203.4 vs -158.4 mL/year, p=0.58) and meta-cohort (-124.0 vs -185.9 mL/year, p=0.25).

Conclusions: Even in the presence of a UIP CT pattern, there may still be differences in lung function over time and survival, particularly for CTD-ILD.