Context: Primary hyperparathyroidism (PH) is characterized by inappropriate PTH elevation with or without hypercalcemia. Bone disease involves catabolic action at cortical sites, while cancellous sites and geometry might be relatively preserved.

Objective: To examine the effect of PH on quantitative and qualitative bone characteristics using peripheral quantitative computed tomography (pQCT) at the tibia in postmenopausal women with PH and healthy controls.

Design: Cross-sectional study

Setting: Tertiary referral center

Patients: Fifty-two postmenopausal women with PH and 56 healthy controls, comparable for age and anthropometric measures.

Intervention: None

Main Outcome Measure: vBMD, BMC, cortical thickness, cortical and trabecular area, peri- and endosteal circumference and polar stress strength index (SSIp) assessed by pQCT of left tibia at 4% (cancellous), 14% (transition zone) and 38% (cortical) from the distal end.

Results: At 4% there was a significant decrease of trabecular BMC and vBMD (P < 0.001), effect particularly evident in hypercalcemic patients, while trabecular area was comparable. At 38% cortical BMC (P < 0.01), vBMD (P < 0.01), area (P < 0.05) and thickness (P < 0.001) were reduced in PH group, particularly in hypercalcemic patients. Endosteal circumference increased (P < 0.001), while periosteal circumference was comparable, indicating cancellization of cortical bone. At 14% SSIp was significantly decreased (P < 0.01) in hypercalcemic patients, indicating impairment of bone mechanical properties.

Conclusions: Normocalcemic PH is characterized by catabolic actions at both cortical and cancellous sites (38% and 4%, respectively), effect accentuated in hypercalcemic patients. Cortical geometric properties are adversely affected even in normocalcemic patients, while trabecular properties are generally preserved.