Interstitial Lung Abnormalities, Emphysema, and Spirometry in Smokers

Most pulmonary conditions reduce FVC, but studies of patients with combined pulmonary fibrosis and emphysema demonstrate that reductions in FVC are less than expected when these two conditions coexist clinically.Do interstitial lung abnormalities (ILAs), chest CT imaging findings that may suggest an early stage of pulmonary fibrosis in individuals with undiagnosed disease, affect the association between emphysema and FVC?Measures of ILA and emphysema were available for 9,579 and 5,277 participants from phases 1 (2007-2011) and 2 (2012-2016) of the Genetic Epidemiology of Chronic Obstructive Pulmonary Disease Study (COPDGene), respectively. ILA were defined by Fleischner Society guidelines. Adjusted linear regression models were used to assess the associations and interactions among ILA, emphysema, measures of spirometry, and lung function.ILA were present in 528 (6%) and 580 (11%) of participants in phases 1 and 2 of COPDGene, respectively. ILA modified the association between emphysema and FVC (P < .0001 for interaction) in both phases. In phase 1, in those without ILA, a 5% increase in emphysema was associated with a reduction in FVC (-110 mL; 95% CI, -121 to -100 mL; P < .0001); however, in those with ILA, it was not (-11 mL; 95% CI, -53 to 31; P = .59). In contrast, no interaction was found between ILA and emphysema on total lung capacity or on diffusing capacity of carbon monoxide.The presence of ILA attenuates the reduction in FVC associated with emphysema.