On the mechanism of cancellous bone preservation in postmenopausal women with mild primary hyperparathyroidism

Several studies have demonstrated that cancellous bone mass and architectur e are preserved in postmenopausal women with primary hyperparathyroidism (P HPT). To investigate the mechanism(s) that could account for this observati on, we analyzed features of bone formation in 19 postmenopausal women with PHPT by bone histomorphometry. The results were compared with those from a comparable group of 34 healthy, postmenopausal women. Patients with PHPT we re similar to control subjects in cancellous bone area as well as in trabec ular width, separation, and number. However, in PHPT, elevations were obser ved in indexes of bone turnover, such as eroded surface, osteoid surface, m ineralizing surface, bone formation rate at the tissue level, and activatio n frequency. At the level of the bone-remodeling unit, women with PHPT had significantly higher values for the wall width of trabecular bone packets ( 40.26 +/- 0.36 vs. 34.58 +/- 0.45 mm), the adjusted apposition rate (0.40 /- 0.04 us. 0.29 +/- 0.03 mm/day), and the active formation period (67.8 +/ - 5.1 vs. 57.3 +/- 2.3 days). These findings are consistent with a stimulat ory action of elevated PTH levels on the duration of the active bone format ion phase in individual remodeling units and may account at least in part f or the preservation of cancellous bone in postmenopausal women with mild PH PT.