Bone histomorphometry in hypoparathyroid patients treated with vitamin D.

Parathyroid hormone (PTH) and vitamin D are both active regulators of bone remodeling. Several studies, mostly in animals and in vitro, have suggested that the two hormones act synergistically or interdependently. The aim of the present study was therefore to describe the actions of vitamin D alone on bone remodeling in the absence of circulating PTH. Bone biopsies were obtained from 12 patients with vitamin D-treated hypoparathyroidism and from 13 age- and gender-matched normal controls. Mean total resorption rate was reduced (0.9 vs. 3.8 mu m/day,p < 0.001), the resorption period was prolonged (80.8 vs. 25.7 days, p < 0.001), and the resorption depth was reduced (41.7 vs. 55.3 mu m, p < 0.001). The fractional active and the total eroded surface were not significantly reduced. The fractional formation surface was reduced (5.2 vs. 12.5 mu m, p < 0.001). Trends toward prolongation of the formation period and reduction of the final wall thickness were found. The balance between resorption depth and final wall thickness was not significantly different from normal (0.96 vs. -4.4 mu m). The quiescent period was prolonged (7.6 vs. 1.7 years, p < 0.001) and the activation frequency was reduced (0.13 vs. 0.6 year(-1), p < 0.001). The structural parameters, trabecular bone volume, trabecular thickness, marrow space star volume, and trabecular star volume, remained unchanged. In the absence of PTH, Vitamin D alone is not able to normalize bone resorption and bone turnover in hypoparathyroid patients.