The Relationship Between Regional Bone Turnover Measured Using ¹⁸F-fluoride Positron Emission Tomography and Changes in BMD Is Equivalent to That Seen for Biochemical Markers of Bone Turnover

Abstract 

Bone turnover is an important determinant of fracture risk. ¹⁸F-fluoride positron emission tomography (¹⁸F-PET) allows the direct assessment of bone turnover at the clinically important skeletal sites such as the lumbar spine. The aim of this study was to determine if the relationship between regional bone turnover measured using ¹⁸F-PET and changes in bone mineral density (BMD) is equivalent to that seen for global skeletal measurements of biochemical markers of bone turnover. Forty-three women who had previously had an ¹⁸F-PET scan at the lumbar spine, assessment of biochemical markers of bone turnover, and a dual-energy X-ray absorptiometry scan of BMD at the lumbar spine and hip (baseline assessments) were split into 1 of 2 groups: (1) 22 women who commenced treatment for osteoporosis within 2mo of having the baseline assessments (Treatment group); (2) 21 women who had not taken any treatments for osteoporosis since having the baseline assessments (Untreated group). Sixteen of the women in the Treatment group started risedronate therapy as part of a prospective study they were participating in, whereas the decision to treat the remaining 6 women was made by the subject's treating physician. Subjects had between 2 and 5 BMD scans over a median follow-up time of 4.1yr to estimate the annual percentage change in BMD since baseline. The relationship between the tertiles of ¹⁸F-PET skeletal kinetic parameter K_i, reflecting regional bone turnover, and annual changes in lumbar spine and hip BMD were compared to that seen for bone formation (bone-specific alkaline phosphatase, BSALP) and bone resorption (urinary deoxypyridinoline) markers. Treated women in the highest tertile of both regional (¹⁸F-PET) and global (biochemical markers) bone turnover showed the greatest annual percentage increases in lumbar spine BMD. The annual increase in lumbar spine BMD was 1.8%, 2.2%, and 3.2% for women in the lowest, middle, and highest tertile of BSALP, respectively, which was similar to that obtained for the regional measurement of K_i of 1.7%, 2.2%, and 2.7% respectively. Untreated women in the highest tertile of regional and global bone turnover had larger decreases in lumbar spine BMD compared to those women in the lowest tertile, with a 1.4- to 4.8-fold difference in the annual decrease in BMD between the two. Less consistent patterns were observed when assessing the relationship between regional and global bone turnover with changes in hip BMD. This study has demonstrated that the relationship between regional bone turnover measured directly at the lumbar spine with changes in BMD is similar to that seen for global skeletal bone turnover using biochemical markers.

Key Words: Biochemical markers, bone mineral density, bone turnover, osteoporosis