Severe Cortical and Trabecular Osteopenia in Secondary Hyperparathyroidism

BACKGROUND: Peripheral quantitative computed tomography (pQCT) provides real volumetric bone density values, not only of the total, but also of trabecular and cortical bone, separately. In addition, it provides data on bone geometry that can be related to the risk of fracture. METHODS: Total, cortical, and trabecular volumetric bone mineral densities (BMD), as well as the main geometric parameters (cross-sectional area, cortical area, trabecular area, and cortical thickness) were assessed by pQCT at the distal radius in 24 hemodialysis patients affected by severe secondary hyperparathyroidism (PTH, mean +/- SD: 1444 +/- 695 pg/mL). The strength-strain index (SSI), a biomechanical parameter describing bone fragility, was also determined. RESULTS: Compared with a control group of 64 healthy age-matched subjects, volumetric BMD (mg/cm(3)) was significantly reduced in all patients (total BMD: 243 +/- 87 vs. 405 +/- 138, cortical BMD: 605 +/- 218 vs. 856 +/- 204, trabecular BMD: 95 +/- 51 vs. 182 +/- 75). Cortical area and cortical thickness showed significant modifications, while cross-sectional area did not. SSI was significantly reduced (547 +/- 125 vs. 927 +/- 306 mm(3)). PTH levels showed a significant inverse correlation with cortical BMD (r = -0.56), cortical thickness (r = -0.46), cortical area (r = -0.61), and SSI (r = -0.54). Quantitative analysis of bone demonstrated cortical porosity. CONCLUSIONS: In dialysis patients with severe secondary hyperparathyroidism, pQCT showed a significant cortical osteopenia, associated with geometric and mechanical bone impairment. Interestingly, we also found a comparable deficit of trabecular bone, which may be related to the very high PTH levels. Generalized cortical thinning, intracortical porosity and cortical-endosteal resorption ("trabecularization" of the cortical bone) are major determinants of reduced bone strength, which may be quantitated by pQCT.