Bone density is associated with emphysema and air trapping on CT in smokers

Background: Osteoporosis is more common in patients with chronic obstructive pulmonary disease (COPD) and smokers. Bone density derived from computed tomography (CT) can be used to identify patients at risk for a vertebral fracture.Aims and objectives: We investigated whether COPD related measures on computed tomography (CT) scans were associated with lower bone density or vertebral fractures in smokers with and without COPD.Methods: We included participants from the NELSON lung cancer screening trial. Bone density was measured as the Hounsfield Unit (HU) in the first lumbar vertebra and vertebral fractures were assessed semi-quantitatively. The 15th Percentile method (Perc15) was used to assess emphysema and the airway lumen perimeter (Pi10) was used to measure airway wall thickness. The expiratory/inspiratory-ratioMeanLungDensity (E/I-ratioMLD) was used as a measure for air trapping and tracheal index (TI) was used to assess trachea deformity.Results: 1,093 male participants were included. Lower Perc15 and higher E/I-ratioMLD were significantly associated with lower bone density (b = -1.29, p = 0.03 and b = -0.48, p = 0.01, respectively). Pi10 and TI were not associated with bone density changes. 95 (8.7\%) participants had a vertebral fracture. All CT-derived biomarkers were not associated with fracture prevalence.Conclusions: Bone density is lower with increasing extents of emphysema and small airway disease, but is not associated with large airway disease and trachea deformity. This may indicate the necessity to measure bone density early in the disease in COPD patients with emphysema and air trapping to prevent vertebral fractures.