Prevalence, detection, and trajectory of combined pulmonary fibrosis and emphysema.
BACKGROUND Combined pulmonary fibrosis and emphysema (CPFE) is an important phenotype in patients with fibrotic interstitial lung disease (ILD). RESEARCH QUESTIONS (1) What is the prevalence of CPFE? (2) What is the predictive performance of the CPFE Index and of physiological airflow obstruction for computed tomography (CT) emphysema extents? (3) Is extent of CT emphysema associated with outcomes in patients with fibrotic ILD? STUDY DESIGN AND METHODS Consecutive patients with idiopathic pulmonary fibrosis (IPF) and non-IPF fibrotic ILD who had a standardized visual assessment of the baseline high-resolution CT chest from a prospective registry were included. CPFE was defined as CT emphysema extent of ≥15%, with sensitivity analyses using different thresholds: ≥5%, ≥10%, and ≥20%. Emphysema subtypes were categorized based on their predominant distribution: centrilobular, paraseptal, or panlobular. The CPFE Index was derived using measurements of spirometry and diffusion capacity for carbon dioxide. RESULTS The prevalence of CPFE at baseline was 20% for IPF (92/455) and 7% in non-IPF fibrotic ILD (84/1121). Both FEV1/FVC ratio < lower limit of normal and <0.70 had poor sensitivity (IPF: 11.1-18.9%; non-IPF fibrotic ILD: 13.1-23.7%) for detecting CT emphysema, although high specificity (IPF: 96.2-98.8%; non-IPF fibrotic ILD: 92.8-95.8%). The CPFE Index was moderately correlated with CT emphysema extent in both IPF (r=0.48) and non-IPF fibrotic ILD (r=0.41), but with poor agreement and wide limits of agreement on Bland-Altman analysis. CT emphysema extent ≥20% was consistently associated with differences in lung function trajectories and worse transplant-free survival in IPF and non-IPF fibrotic ILD. There were no significant relationships between emphysema subtypes and health outcomes.