Quantitative Vertebral Bone Density Seen on Chest CT in Chronic Obstructive Pulmonary Disease Patients: Association with Mortality in the Korean Obstructive Lung Disease Cohort

OBJECTIVE: Patients with chronic obstructive pulmonary disease (COPD) are known to be at risk of osteoporosis. The purpose of this study was to evaluate the association between thoracic vertebral bone density measured on chest CT (D(Thorax)) and clinical variables, including survival, in patients with COPD. MATERIALS AND METHODS: A total of 322 patients with COPD were selected from the Korean Obstructive Lung Disease (KOLD) cohort. D(Thorax) was measured by averaging the CT values of three consecutive vertebral bodies at the level of the left main coronary artery with a round region of interest as large as possible within the anterior column of each vertebral body using an in-house software. Associations between D(Thorax) and clinical variables, including survival, pulmonary function test (PFT) results, and CT densitometry, were evaluated. RESULTS: The median follow-up time was 7.3 years (range: 0.1–12.4 years). Fifty-six patients (17.4%) died. D(Throax) differed significantly between the different Global Initiative for Chronic Obstructive Lung Disease stages. D(Throax) correlated positively with body mass index (BMI), some PFT results, and the six-minute walk distance, and correlated negatively with the emphysema index (EI) (all p < 0.05). In the univariate Cox analysis, older age (hazard ratio [HR], 3.617; 95% confidence interval [CI], 2.119–6.173, p < 0.001), lower BMI (HR, 3.589; 95% CI, 2.122–6.071, p < 0.001), lower forced expiratory volume in one second (FEV(1)) (HR, 2.975; 95% CI, 1.682–5.262, p < 0.001), lower diffusing capacity of the lung for carbon monoxide corrected with hemoglobin (DL(CO)) (HR, 4.595; 95% CI, 2.665–7.924, p < 0.001), higher EI (HR, 3.722; 95% CI, 2.192–6.319, p < 0.001), presence of vertebral fractures (HR, 2.062; 95% CI, 1.154–3.683, p = 0.015), and lower D(Thorax) (HR, 2.773; 95% CI, 1.620–4.746, p < 0.001) were significantly associated with all-cause mortality and lung-related mortality. In the multivariate Cox analysis, lower D(Thorax) (HR, 1.957; 95% CI, 1.075–3.563, p = 0.028) along with older age, lower BMI, lower FEV(1), and lower DL(CO) were independent predictors of all-cause mortality. CONCLUSION: The thoracic vertebral bone density measured on chest CT demonstrated significant associations with the patients' mortality and clinical variables of disease severity in the COPD patients included in KOLD cohort.