Differing effects of PTH 1-34, PTH 1-84, and zoledronic acid on bone microarchitecture and estimated strength in postmenopausal women with osteoporosis: An 18-month open-labeled observational study using HR-pQCT

Whereas the beneficial effects of intermittent treatment with parathyroid hormone (PTH) (intact PTH 184 or fragment PTH 134, teriparatide) on vertebral strength is well documented, treatment may not be equally effective in the peripheral skeleton. We used high-resolution peripheral quantitative computed tomography (HR-pQCT) to detail effects on compartmental geometry, density, and microarchitecture as well as finite element (FE) estimated integral strength at the distal radius and tibia in postmenopausal osteoporotic women treated with PTH 134(20 mu g sc daily, n=18) or PTH 184(100 mu g sc daily, n=20) for 18 months in an open-label, nonrandomized study. A group of postmenopausal osteoporotic women receiving zoledronic acid (5mg infusion once yearly, n=33) was also included. Anabolic therapy increased cortical porosity in radius (PTH 134 32 +/- 37%, PTH 184 39 +/- 32%, both p<0.001) and tibia (PTH 134 13 +/- 27%, PTH 184 15 +/- 22%, both p<0.001) with corresponding declines in cortical density. With PTH 134, increases in cortical thickness in radius (2.0 +/- 3.8%, p<0.05) and tibia (3.8 +/- 10.4%, p<0.01) were found. Trabecular number increased in tibia with both PTH 134 (4.2 +/- 7.1%, p<0.05) and PTH 184 (5.3 +/- 8.3%, p<0.01). Zoledronic acid did not impact cortical porosity at either site but increased cortical thickness (3.0 +/- 3.5%, p<0.01), total (2.7 +/- 2.5%, p<0.001) and cortical density (1.5 +/- 2.0%, p<0.01) in tibia as well as trabecular volume fraction in radius (2.5 +/- 5.1%, p<0.05) and tibia (2.2 +/- 2.2%, p<0.01). FE estimated bone strength was preserved, but not increased, with PTH 134 and zoledronic acid at both sites, whereas it decreased with PTH 184 in radius (2.8 +/- 5.8%, p<0.05) and tibia (3.9 +/- 4.8%, p<0.001). Conclusively, divergent treatment-specific effects in cortical and trabecular bone were observed with anabolic and zoledronic acid therapy. The finding of decreased estimated strength with PTH 184 treatment was surprising and warrants confirmation. (c) 2013 American Society for Bone and Mineral Research.