Relationship of annual change in bone mineral density with extent of emphysematous lesions and pulmonary function in patients with COPD

Kenichi Goto,^1,2 Emiko Ogawa,^1,3 Kaoruko Shimizu,⁴ Hironi Makita,⁴ Hidenobu Suzuki,⁵ Yoshiki Kawata,⁵ Noboru Niki,⁵ Masaharu Nishimura,⁴ Yasutaka Nakano<sup>1

1</sup>Division of Respiratory Medicine, Department of Medicine, Shiga University of Medical Science, Otsu, Shiga, ²Department of Pulmonary Medicine, Takatsuki Red Cross Hospital, Takatsuki, Osaka, ³Health Administration Center, Shiga University of Medical Science, Otsu, Shiga, ⁴First Department of Medicine, Hokkaido University Hospital, Sapporo, Hokkaido, ⁵Institute of Technology and Science, Tokushima University, Tokushima, Tokushima, Japan

Background: Osteoporosis is a well-known comorbidity in COPD. It is associated with poor health status and prognosis. Although the exact pathomechanisms are unclear, osteoporosis is suggested to be either a comorbidity due to shared risk factors with COPD or a systematic effect of COPD with a cause–effect relationship. This study aimed to evaluate whether progression of osteoporosis is synchronized with that of COPD.
Materials and methods: Data from 103 patients with COPD included in the Hokkaido COPD cohort study were analyzed. Computed tomography (CT) attenuation values of thoracic vertebrae 4, 7, and 10 were measured using custom software, and the average value (average bone density; ABD_4,7,10) was calculated. The percentage of low attenuation volume (LAV%) for each patient was also calculated for evaluation of emphysematous lesions. Annual change in thoracic vertebral CT attenuation, which is strongly correlated with dual-energy X-ray absorptiometry-measured bone mineral density, was compared with that in FEV_1.0 or emphysematous lesions.
Results: In the first CT data set, ABD_4,7,10 was significantly correlated with age (ρ=–0.331; p=0.0006), body mass index (BMI; ρ=0.246; p=0.0136), St George’s Respiratory Questionnaire (SGRQ) activity score (ρ=–0.248; p=0.0115), eosinophil count (ρ=0.229; p=0.0198), and LAV% (ρ=–0.372; p=0.0001). However, ABD_4,7,10 was not associated with FEV_1.0. After adjustment for age, BMI, SGRQ activity score, and eosinophil count, no significant relationship was found between ABD_4,7,10 and LAV%. Annual change in ABD_4,7,10 was not associated with annual change in LAV% or FEV_1.0.
Conclusion: Progression of osteoporosis and that of COPD are not directly related or synchronized with each other.

Keywords: osteoporosis, quantitative CT analysis, FEV_1.0, low attenuation volume, automatic analysis, systemic effect