Site specific differences in vBMD and geometry in postmenopausal women with primary hyperparathyroidism

Primary Hyperparathyroidism (PHPT) is associated with catabolic effects at both trabecular and cortical bone. Mechanical loading is one of the most important natural anabolic stimuli for bone at all ages. The present study was designed to assess the impact of PHPT on vBMD and bone geometry using peripheral quantitative computed tomography (pQCT) at the radius and tibia, sites with similar structural characteristics, but subject to different loading conditions.

We evaluated the impact of PHPT on bone, by comparing the z-scores of volumetric Bone Mineral Density (vBMD) and indices of bone geometry simultaneously at the tibia and the radius by pQCT, skeletal sites with similar structure, but subject to different loading conditions. Forty-one postmenopausal women with PHPT and 79 controls, comprised the study group.

At both trabecular and cortical sites, vBMD and bone geometry indices were significantly lower in patients compared with controls. In patients with PHPT, apart from a lower z-score for total vBMD (p = 0.01) at the radius, there was no other difference between the radius and the tibia at the trabecular sites. On the contrary, at cortical sites, the z-scores of cortical bone mineral content (p = 0.02), cortical vBMD (p = 0.01) and cortical cross-sectional area (p = 0.05) were significantly lower at the radius compared with the tibia, indicating that cortical bone at the weight bearing tibia might be less affected by the catabolic actions of continuous parathyroid hormone (PTH) exposure. PTH levels were positively associated with the difference in z-scores of cort BMD (r = 0.439, p < 0.01) indicating that in more severe cases, as expressed by higher PTH levels, the deleterious effects at the non-weight bearing radius might be accentuated.

We found that in postmenopausal women with PHPT, both trabecular and cortical bone are adversely affected. However, at the weight bearing tibia as compared with the radius, the deleterious effects, especially on cortical bone, seem to be attenuated.

NCT05426512, 21/06/2022, "retrospectively registered".