Effects of salmon calcitonin on trabecular microarchitecture as determined by magnetic resonance imaging: Results from the QUEST study

Introduction: It is postulated that the reduction in osteoporotic fracture risk in response to certain antiresorptive osteoporosis therapies is caused less by effects on bone quantity than on bone quality (specifically trabecular microarchitecture). To test this hypothesis, the QUEST study was conducted to assess the effects of nasal spray salmon calcitonin (CT-NS) or placebo on parameters of trabecular microarchitecture at multiple skeletal sites using noninvasive MRI technology and iliac crest bone biopsies by mu CT/histomorphometry. Materials and Methods: Ninety-one postmenopausal osteoporotic women were followed for 2 years (n = 46 for CT-NS, n = 45 for placebo); all women received 500 mg calcium daily. MRI measurements at distal radius, hip (T2 relaxation time [T2*]), and os calcis (obtained yearly), iliac crest bone biopsies with 2D histomorphometry and 3D mu CT (obtained at study onset and conclusion), DXA-BMD at spine/hip/wrist/os calcis (obtained yearly), and markers of bone turnover (obtained at 2-week to 12-month intervals) were analyzed, with an analysis of covariance model used to assess treatment effect for parameters of interest. Results and Conclusions: MRI assessment of trabecular microarchitecture at individual regions of the distalradius revealed significant improvement, or preservation (no significant loss), in the CT-NS-treated group compared with significant deterioration in the placebo control group, as reflected in apparent BV/TV (p < 0.03), apparent trabecular number (p < 0.01), and apparent trabecular spacing (p < 0.01). Also, at the hip, the CT-NS group exhibited preservation of trabecular microarchitecture at the lower trochanter (p < 0.05) as determined by T2* MRI technology. Significant deterioration of trabecular bone architecture was noted in the placebo group at the femoral neck, Ward's triangle, and lower trochanteric sites. Apart from a significant increase in apparent trabecular number in the CT-NS group, significant changes within or between groups were not noted at the os calcis. Combined LCT/histomorphometric analysis of iliac crest bone biopsies did not reveal significant differences between treated and placebo groups. In the CT-NS group, regardless of the change in BMD (gain or loss) at the spine, hip, or distal radius, preservation of parameters of trabecular microarchitecture was noted, whereas in the placebo group, regardless of the change in BMD (gain or loss) at the spine, hip, or distal radius, loss or preservation was noted; however, changes in DXA/BMD (of the spine, hip, wrist, os calcis) between CT-NS and placebo groups were not significant. Serum C-telopeptide (S-M), a specific bone resorption marker, was reduced by 22.5 % at 24 months (p = 0.056). The results of the QUEST study suggest therapeutic benefit of CT-NS compared with placebo in maintaining trabecular microarchitecture at multiple skeletal sites and support the use of MRI technology for assessment of trabecular microarchitecture in clinical research trials. However, the results also highlight site specific differences in response to antiresorptive therapies and the importance of sufficiently large sampling volumes (areas) to obtain reliable assessment of bone architecture.