TNFRSF11B and pulmonary emphysema: In conclusion, our study demonstrated that the extent of pulmonary emphysema was significantly correlated with reduced bone density, and for the first time to our knowledge, that the level of RANKL and the RANKL/OPG ratio were significantly higher in COPD patients with low BMD compared to those with normal BMD, and correlated negatively with lumbar vertebral BMD, but positively with LAA%.