Prevalence of interstitial lung disease (ILD) in a lung cancer screening program using low-dose computer tomography (CT)

Introduction: The prevalence of ILD in asymptomatic smokers is unknown. Unsuspected ILD can easily be detected by low-dose screening CTs. Materials and methods: We conducted a retrospective review of CTs from 2418 individuals enrolled in the University of Navarre's lung cancer screening program between 2003 and 2010. Subjects were asymptomatic current or former smokers at least 40 years old, with a cumulative tobacco exposure > 10 pack-years. The prevalence of ILD on baseline CT was assessed initially by 2 independent radiologists. ILD was confirmed and characterized by a panel including a third radiologist and a pulmonologist. Results: The prevalence of ILD in our study was 1.8%. The median age of subjects with ILD was 57 years (IQR: 51-68). Most were male (70%) and continued to smoke (71%) with a cumulative tobacco exposure of 35 pack-years (IQR: 23-47). The most common radiographic pattern was reticular disease (68%), followed by ground glass opacities (59%), bronchiolitis (15%), honeycombing (11%), and nodular (5%). The majority of subjects had peripheral (77%) and bilateral (96%) disease. Lymphadenopathy was rare (9%). The prevalence of emphysema in subjects with ILD was high (80%). Bronchial wall thickening (59%) and coronary calcifications (46%) were also common. Lung function was preserved in this asymptomatic cohort with a mean FEV1 of 97% (IQR: 78-108). Conclusions: The prevalence of ILD in our screening population was higher than expected. Most of these individuals ignore the diagnosis, continue smoking, and have preserved lung function.