Hiperparatireoidismo primário: novas perspectivas sobre qualidade óssea através da avaliação por tomografia computadorizada quantitativa periférica de alta resolução e escore de osso trabecular

Abstract

Introduction: Primary hyperparathyroidism (PHPT) is predominantly an asymptomatic disease, diagnosed by the fortuitous finding of hypercalcemia. Typically, in this milder form of the disease, areal bone mineral density (aBMD) by DXA is reduced at the 1/3 radius, a site of predominantly cortical bone, while the lumbar spine, a site of predominantly cancellous bone, is generally well preserved. Histomorphometric and micro-computed tomography (µCT) analyses of iliac crest bone biopsies have confirmed these DXA results in PHPT by showing reduced cortical elements whereas the trabecular compartment appears to be relatively well preserved. These findings, however, are inconsistent with numerous epidemiological reports showing an increased in fracture risk at both vertebral and non-vertebral sites in PHPT. Emerging technologies, such as high-resolution peripheral quantitative computed tomography (HRpQCT), and trabecular bone score (TBS) may provide additional insight into microstructural features and bone quality in PHPT. Moreover, individual trabecula segmentation (ITS) and finite element analysis (FEA) of HRpQCT images offer even more detailed information about trabecular bone and bone stiffness, estimating the biomechanical competence of bone, and fracture risk inPHPT Aims: To evaluate both cortical and trabecular compartments by HRpQCT and FEA, and the trabecular compartment by ITS analysis, in postmenopausal women with PHPT, as compared to healthy controls. To correlate TBS with HRpQCT measurements in PHPT. Patients and Methods: HRpQCT, ITS and FE analyses were performed in 51 postmenopausal women with PHPT and 120 controls. TBS was assessed in a subgroup of 22 women with PHPT. Results: aBMD at the lumbar spine by DXA was similar in cases and controls. However, women with PHPT showed, at both sites, decreased volumetric densities at trabecular and cortical compartments, thinner cortices, and more widely spaced and heterogeneously distributed trabeculae. At the radius, trabeculae were thinner and fewer in PHPT. The radius was affected to a greater extent in the trabecular compartment than the tibia. ITS analyses revealed, at both sites, that plate-like trabeculae were depleted, with a resultant reduction in the plate/rod ratio. Microarchitectural abnormalities were evident by decreased plate-rod and plate-plate junctions at the radius and tibia, and rod-rod junctions at the radius. These trabecular and cortical abnormalities resulted in decreased whole bone stiffness and trabecular stiffness. TBS was correlated with all HRpQCT and mechanical measurements except for trabecular thickness (Tb.Th), and trabecular stiffness at the radius. At the tibia, correlations were observed between TBS and volumetric densities, cortical thickness, trabecular bone volume, and whole bone stiffness. All indices of trabecular microarchitecture, except Tb.Th, correlated with TBS after adjusting for body weight. Conclusion: These results provide evidence that in PHPT, reduced volumetric densities and microstructural abnormalities are pervasive and not limited to the cortical compartment. These abnormalities seen by HRpQCT are likely to reflect reduced bone strength and may help to account for increased global fracture risk in PHPT. With significant correlations of TBS with mechanical and microstructural indices by HRpQCT, a method that is not generally available, TBS could become a helpful clinical tool in the assessment of trabecular microstructure in PHPT.