Association of bone mineral density with airway obstruction and emphysema

Background: Airway obstruction and the extent of emphysema are reported to be responsible for reduced bone mineral density (BMD). Corresponding to different phenotypes of a pulmonary disease, different severity in extra pulmonary features may exist. We compared BMDs of subjects with or without airway obstruction and/or emphysema and investigated the relationships among BMD, the severity of airway obstruction, and the extent of emphysema.

Methods: Using a university hospital database, we reviewed patients over 40 years old who performed spirometry, computed tomography of chest, and measurement of BMD of the lumbar (L) spine. According to the presence or absence of airway obstruction and/or emphysema, four groups were classified.

Results: Among a total of 59 subjects, 33 (56%) had osteoporosis. The prevalence of osteoporosis in subjects with no airway obstruction and no emphysema, those with only emphysema, those with only airway obstruction, and those with both airway obstruction and emphysema were 42%, 57%, 64%, and 73%, respectively (p=0.047 by linear-by-linear association). The mean T-scores of BMD of L1 (p=0.032) and L1-4 spines were different among the four groups (p=0.034). Although the T-score of L1 BMD negatively correlated with the extent of emphysema (r=-0.275, p=0.035) and positively with each of body mass index (BMI) (r=0.520, p<0.001), forced expiratory volume in one second (FEV(1)) (r=0.330, p=0.011), FEV(1)/forced vital capacity (r=0.409, p=0.001), and forced expiratory flow at 25~75% of FVC (FEF(25-75%)) (r=0.438, p=0.0001), respectively, multiple linear regression analysis indicated that BMI (p<0.001) and FEF(25-75%) were predictive of BMD (p=0.012).

Conclusion: Low BMI and airway obstruction were strongly associated with reduced bone density rather than the extent of emphysema.