Differential effects of teriparatide on regional bone formation using ¹⁸F‐fluoride positron emission tomography

Abstract Teriparatide increases skeletal mass, bone turnover markers, and bone strength, but local effects on bone tissue may vary between skeletal sites. We used positron emission tomography (PET) to study 18F-fluoride plasma clearance (Ki) at the spine and standardized uptake values (SUVs) at the spine, pelvis, total hip, and femoral shaft in 18 postmenopausal women with osteoporosis. Subjects underwent a 1-hour dynamic scan of the lumbar spine and a 10-minute static scan of the pelvis and femurs at baseline and after 6 months of treatment with 20 µg/day teriparatide. Blood samples were taken to derive the arterial input function and lumbar spine Ki values evaluated using a three-compartment model. SUVs were calculated for the spine, pelvis, total hip, and femoral shaft. After 6 months treatment with teriparatide, spine Ki values increased by 24% (p = .0003), while other model parameters were unchanged except for the fraction of tracer going to bone mineral (k3/[k2 + k3]), which increased by 23% (p = .0006). In contrast to Ki, spine SUVs increased by only 3% (p = .84). The discrepancy between changes in Ki and SUVs was explained by a 20% decrease in 18F− plasma concentration. SUVs increased by 37% at the femoral shaft (p = .0019), 20% at the total hip (p = .032), and 11% at the pelvis (p = .070). Changes in bone turnover markers and BMD were consistent with previous trials. We conclude that the changes in bone formation rate during teriparatide treatment as measured by 18F− PET differ at different skeletal sites, with larger increases in cortical bone than at trabecular sites. © 2011 American Society for Bone and Mineral Research.