Changes observed in radionuclide bone scans during and after teriparatide treatment for osteoporosis

Purpose Visual changes on radionuclide bone scans have been reported with teriparatide treatment. To assess this, serial studies were evaluated and quantified in ten postmenopausal women with osteoporosis treated with teriparatide (20 mu g/day subcutaneous) who had Tc-99m-methylene diphosphonate (MDP) bone scans (baseline, 3 and 18 months, then after 6 months off therapy). Methods Women were injected with 600 MBq Tc-99m-MDP, and diagnostic bone scan images were assessed at 3.5 h. Additional whole-body scans (10 min, 1, 2, 3 and 4 h) were analysed for Tc-99m-MDP skeletal plasma clearance (K-bone). Regional K-bone differences were obtained for the whole skeleton and six regions (calvarium, mandible, spine, pelvis, upper and lower extremities). Bone turnover markers (BTM) were also measured. Results Most subjects showed visual changes on 3- and 18-month bone scan images that disappeared after 6 months off therapy. Enhanced uptake was seen predominantly in the calvarium and lower extremities. Whole skeleton K-bone displayed a median increase of 22% (3 months, p=0.004) and 34% (18 months, p=0.002) decreasing to 0.7% (6 months off therapy). Calvarium K-bone changes were three times larger than other sites. After 6 months off therapy, all K-bone and BTM values returned towards baseline. Conclusion The increased Tc-99m-MDP skeletal uptake with teriparatide indicated increased bone formation which was supported by BTM increases. After 6 months off therapy, metabolic activity diminished towards baseline. The modulation of Tc-99m-MDP skeletal uptake during treatment was the result of teriparatide's metabolic activity. These findings may aid the radiological evaluation of similar teriparatide patients having radionuclide bone scans.