The histomorphometry of bone in primary hyperparathyroidism: preservation of cancellous bone structure

Evaluation of the Thiazide Challenge Test to Differentiate Primary From Hypercalciuria-Related Hyperparathyroidism

CONTEXT

Treatment of primary hyperparathyroidism (PHPT) and secondary hyperparathyroidism due to idiopathic hypercalciuria (SHPT-IH) is markedly different. Robust diagnostic tools to differentiate between both entities are however lacking.

OBJECTIVE

Evaluate the thiazide challenge test (TCT) in clinical practice, its aid in clinical decision making, and evaluate the accuracy (sensitivity, specificity) and potentially useful parameters of the TCT.

METHODS

Monocentric observational retrospective cohort study from January 2017 to November 2023 in an outpatient Endocrinology department, Ghent University Hospital (Belgium). Twenty-five adult patients with hypercalciuria, elevated parathyroid hormone (PTH), and high-normal or elevated serum calcium underwent a TCT. Outcome measures were serum, urinary biochemical parameters before and after testing, clinical and imaging outcomes, treatment, and follow-up.

RESULTS

Patients with a TCT-based working diagnosis of PHPT show greater increases in albumin-adjusted calcium and total serum calcium concentration than patients with SHPT-IH (+0.11 ± 0.10 vs +0.0071 ± 0.10 mmol/L; P = .025 and +0.14 ± 0.12 vs +0.012 ± 0.15 mmol/L; P = .024, respectively). The TCT-based working diagnosis of PHPT has a sensitivity of 81.8%, a specificity of 77.8%, and a likelihood ratio of 3.68 of estimating a correct final diagnosis. Urinary calcium excretion, PTH, calcium-phosphorous ratio, PTH inhibition rate, and the parathyroid function index do not differ significantly in patients with PHPT compared with those with SHPT-IH.

CONCLUSION

The TCT aids in discriminating patients with PHPT from those with SHPT-IH based on a rise in serum calcium. Other parameters are not different between both groups. Larger prospective trials are necessary to further define the diagnostic potential of the TCT, its most appropriate biochemical outcome variables, and decision cut-offs.

Chapter 3: Impact of primary hyperparathyroidism

At present, primary hyperparathyroidism is most often discovered in an asymptomatic patient, but can sometimes be revealed by a renal or bone complications. In all cases, a full work-up is recommended, with assessment of renal function (glomerular filtration rate), 24-hour calciuria, screening for risk factors for lithiasis, and renal and urinary tract imaging (ultrasound or CT scan) to look for stones or nephrocalcinosis. Bone densitometry, with measurements of the spine, femur and radius, is the recommended reference test for demineralization. Standard X-rays of the spine or other imaging techniques are recommended for the detection of asymptomatic vertebral fracture. Neurocognitive manifestations, reduced quality of life or cardiovascular manifestations should not be routinely screened for, as they are not currently consensual criteria for surgical indications.

Bone quality in endocrine diseases: determinants and clinical relevance

PURPOSE

Bone is one of the main targets of hormones and endocrine diseases are frequent causes of secondary osteoporosis and fractures in real-world clinical practice. However, diagnosis of skeletal fragility and prediction of fractures in this setting could be a challenge, since the skeletal alterations induced by endocrine disorders are not generally captured by dual-energy X-ray absorptiometry (DXA) measurement of bone mineral density (BMD), that is the gold standard for diagnosis of osteoporosis in the general population. The aim of this paper is to review the existing evidence related to bone quality features in endocrine diseases, proposing assessment with new techniques in the future.

METHODS

A comprehensive search within electronic databases was performed to collect reports of bone quality in primary hyperparathyroidism, hypoparathyroidism, hyperthyroidism, hypercortisolism, growth hormone deficiency, acromegaly, male hypogonadism and diabetes mellitus.

RESULTS

Using invasive and non-invasive techniques, such as high-resolution peripheral quantitative computed tomography or DXA measurement of trabecular bone score (TBS), several studies consistently reported altered bone quality as predominant determinant of fragility fractures in subjects affected by chronic endocrine disorders.

CONCLUSIONS

Assessment of skeletal fragility in endocrine diseases might take advantage from the use of techniques to detect perturbation in bone architecture with the aim of best identifying patients at high risk of fractures.

Comparison of bone microstructures via high-resolution peripheral quantitative computed tomography in patients with different stages of chronic kidney disease before and after starting hemodialysis

Chronic kidney disease (CKD) negatively affects bone strength; however, the osteoporotic conditions in patients with CKD are not fully understood. Moreover, the changes in bone microstructure between pre-dialysis and dialysis are unknown. High-resolution peripheral quantitative computed tomography (HR-pQCT) reveals the three-dimensional microstructures of the bone. We aimed to evaluate bone microstructures in patients with different stages of CKD. This study included 119 healthy men and 40 men admitted to Nagasaki University Hospital for inpatient education or the initiation of hemodialysis. The distal radius and tibia were scanned with HR-pQCT. Patient clinical characteristics and bone microstructures were evaluated within 3 months of initiation of hemodialysis (in patients with CKD stage 5 D), patients with CKD stage 4-5, and healthy volunteers. Cortical bone parameters were lower in the CKD group than in healthy controls. Tibial cortical and trabecular bone parameters (cortical thickness, cortical area, trabecular volumetric bone mineral density, trabecular-bone volume fraction, and trabecular thickness) differed between patients with CKD stage 5 D and those with CKD stage 4-5 (p < 0.01). These differences were also observed between patients with CKD stage 5 and those with CKD stage 5 D (p < 0.017), but not between patients with CKD stage 4 and those with CKD stage 5, suggesting that the bone microstructure rapidly changed at the start of hemodialysis. Patients with CKD stage 5 D exhibited tibial microstructural impairment compared with those with CKD stage 4-5. HR-pQCT is useful for elucidation of the pathology of bone microstructures in patients with renal failure.

Irisin and Bone in Sickness and in Health: A Narrative Review of the Literature

Irisin is a hormone-like myokine produced by the skeletal muscle in response to exercise. Upon its release into the circulation, it is involved in the browning process and thermogenesis, but recent evidence indicates that this myokine could also regulate the functions of osteoblasts, osteoclasts, and osteocytes. Most human studies have reported that serum irisin levels decrease with age and in conditions involving bone diseases, including both primary and secondary osteoporosis. However, it should be emphasized that recent findings have called into question the importance of circulating irisin, as well as the validity and reproducibility of current methods of irisin measurement. In this review, we summarize data pertaining to the role of irisin in the bone homeostasis of healthy children and adults, as well as in the context of primary and secondary osteoporosis. Additional research is required to address methodological issues, and functional studies are required to clarify whether muscle and bone damage per se affect circulating levels of irisin or whether the modulation of this myokine is caused by the inherent mechanisms of underlying diseases, such as genetic or inflammatory causes. These investigations would shed further light on the effects of irisin on bone homeostasis and bone disease.

Bone Mineral Density Compared to Trabecular Bone Score in Primary Hyperparathyroidism

Individuals with primary hyperparathyroidism (PHPT) have reduced bone mineral density (BMD) according to dual X-ray absorptiometry at cortical sites, with relative sparing of trabecular BMD. However, fracture risk is increased at all sites. Trabecular bone score (TBS) may more accurately describe their bone quality and fracture risk. This study compared how BMD and TBS describe bone quality in PHPT. We conducted a retrospective cross-sectional study with a longitudinal component, of adults with PHPT, admitted to a tertiary hospital in Australia over ten years. The primary outcome was the TBS at the lumbar spine, compared to BMD, to describe bone quality and predict fractures. Secondary outcomes compared changes in TBS after parathyroidectomy. Of 68 included individuals, the mean age was 65.3 years, and 79% were female. Mean ± SD T-scores were −1.51 ± 1.63 at lumbar spine and mean TBS was 1.19 ± 0.12. Only 20.6% of individuals had lumbar spine BMD indicative of osteoporosis, while 57.4% of TBS were ≤1.20, indicating degraded architecture. There was a trend towards improved fracture prediction using TBS compared to BMD which did not reach statistical significance. Comparison of 15 individuals following parathyroidectomy showed no improvement in TBS.

Skeletal abnormalities in Hypoparathyroidism and in Primary Hyperparathyroidism

Both hypoparathyroidism (HypoPT), as well as its pathological counterpart, primary hyperparathyroidism (PHPT), can lead to skeletal abnormalities. Chronic deficiency of PTH in patients with HypoPT is associated with a profound reduction in bone remodeling, with consequent increases in bone density, and abnormalities in microarchitecture and bone strength. It is still not clear whether there is an increase in fracture risk in HypoPT. While standard therapy with calcium supplements and active vitamin D does not restore bone homeostasis, treatment of HypoPT with PTH appears to correct some of those abnormalities. In PHPT, the continuous exposure to high levels of PTH causes an increase in bone remodeling, in which bone resorption prevails. In the symptomatic form of PHPT, patients can present with fragility fractures, and/or the classical radiological features of osteitis fibrosa cystica. However, even in mild PHPT, catabolic skeletal actions of PTH are evident through reduced BMD, deterioration of bone microarchitecture and increased risk of fragility fractures. Successful parathyroidectomy improves skeletal abnormalities. Medical treatment, such as bisphosphonates and denosumab, can also increase bone density in patients with PHPT who do not undergo surgery. This article reviews skeletal involvement in HypoPT and in PHPT, as assessed by bone remodeling, DXA, trabecular bone score, and quantitative computed tomography, as well as data on bone strength and fracture risk. The effects of PTH replacement on the skeleton in subjects with HypoPT, and the outcome of parathyroidectomy in patients with PHPT, are also reviewed here.

The Impact of Observation Versus Parathyroidectomy on Bone Mineral Density and Fracture Risk Determined by FRAX Tool in Patients With Primary Hyperparathyroidism

To study impact of observation (OBV) vs parathyroidectomy (PTX) on biochemistry, bone mineral density (BMD) and fracture risk calculated by Fracture Risk Assessment (FRAX) tool in primary hyperparathyroidism (PHPT). Retrospective study of 60 patients (OBV - 26; PTX - 34 patients). Mean adjusted calcium improved in both groups [OBV - 2.76 ± 0.07 vs 2.51 ± 0.20 mmol/L; p < 0.00001, PTX - 2.87 ± 0.21 vs 2.36 ± 0.12 mmol/L; p < 0.00001]. Mean parathyroid hormone level declined in both but more in PTX group [OBV - 11.4 ± 5.2 vs. 9.7 ± 5.6 pmol/L; p = 0.04, PTX - 14.3 ± 8.2 vs 4.6 ± 2.2 pmol/L; p < 0.00001]. In OBV group, BMD and T scores declined at all sites. Mean percentage change of BMD was -5.8 % at femoral neck (FN), -4.9 % at total hip (TH), -6.2 % at lumbar spine (LS) and -10.0 % at lower 1/3^rd radius (LR). PTX led to stabilization of BMD at FN (3.0 %), TH (-0.6 %) and LS (2.2 %) but significant improvement at LR (13.9 %; p = 0.0005). In OBV group, 10 year risk of hip fracture (HF) (7.5 ± 9.0 % vs. 8.6 ± 9.0; p = 0.01) and major osteoporotic fracture (OF) (16.6 ± 10.9 % vs 18.3 ± 10.8 %; p = 0.002) worsened with time whereas in PTX group, risk of both type of fractures remained stable (HF; p = 0.48 and OF; p = 0.43). Comparison between groups showed greater improvement in median % change of fracture risk for both HF and OF in PTX group. OBV in PHPT lead to greater decline in BMD at all skeletal sites and imparted significant risk of HF and major OF. PTX offered stabilization of BMD at most sites but improvement at LR with unchanged fracture risk. FRAX tool should be used more frequently and universally.

[The clinical practice guidelines for primary hyperparathyroidism, short version]

Primary hyperparathyroidism (PHPT) is an endocrine disorder of parathyroid glands characterized by excessive secretion of parathyroid hormone (PTH) with an upper normal or elevated blood calcium level. Classical PHPT refers to a symptomatic, multi-system disorder, wich can lead to a significant decrease in the quality of life, disability of patients, and even an increased risk of premature death. Hypercalcemia and the catabolic effect of PTH on various cells are considered as the main pathogenetic mechanisms of the PHPT associated complications. In the last two decades, there has been an increase in the incidence of PHPT, mainly due to the mild forms of the disease, primarily due to the routine calcium screening in North America, Western Europe and, Asia. High prevalence of the disease, as well as the variety of clinical manifestations, cause the attention of different specialists - physicians, rheumatologists, urologists, nephrologists, cardiologists and other doctors. This review cover the main issues of Russian guidelines for the management of PHPT, approved in 2020, including laboratory and instrumental methods, differential diagnosis, surgical and conservative approach, short-term and long-term follow-up. This guidelines also include the recommendations for special groups of patients with hereditary forms of PHPT, parathyroid carcinoma, PHPT during pregnancy.

A feline-focused review of chronic kidney disease-mineral and bone disorders - Part 1: Physiology of calcium handling

Mineral derangements are a common consequence of chronic kidney disease (CKD). Despite the well-established role of phosphorus in the pathophysiology of CKD, the implications of calcium disturbances associated with CKD remain equivocal. Calcium plays an essential role in numerous physiological functions in the body and is a fundamental structural component of bone. An understanding of calcium metabolism is required to understand the potential adverse clinical implications and outcomes secondary to the (mal)adaptation of calcium-regulating hormones in CKD. The first part of this two-part review covers the physiology of calcium homeostasis (kidneys, intestines and bones) and details the intimate relationships between calcium-regulating hormones (parathyroid hormone, calcitriol, fibroblast growth factor 23, α-Klotho and calcitonin) and the role of the calcium-sensing receptor.

Impact of Release Kinetics on Efficacy of Locally Delivered Parathyroid Hormone for Bone Regeneration Applications

Characterizing the release profile for materials-directed local delivery of bioactive molecules and its effect on bone regeneration is an important step to improve our understanding of, and ability to optimize, the bone healing response. This study examined the local delivery of parathyroid hormone (PTH) using a thiol-ene hydrogel embedded in a porous poly(propylene fumarate) (PPF) scaffold for bone regeneration applications. The aim of this study was to characterize the degradation-controlled in vitro release kinetics of PTH from the thiol-ene hydrogels, in vivo hydrogel degradation in a subcutaneous implant model, and bone healing in a rat critical size bone defect. Tethering PTH to the hydrogel matrix eliminated the early timepoint burst release that was observed in previous in vitro work where PTH was free to diffuse out of the matrix. Only 8% of the tethered PTH was released from the hydrogel during the first 2 weeks, but by day 21, 80% of the PTH was released, and complete release was achieved by day 28. In vivo implantation revealed that complete degradation of the hydrogel alone occurred by day 21; however, when incorporated in a three-dimensional printed osteoconductive PPF scaffold, the hydrogel persisted for >56 days. Treatment of bone defects with the composite thiol-ene hydrogel-PPF scaffold, delivering either 3 or 10 μg of tethered PTH 1-84, was found to increase bridging of critical size bone defects, whereas treatment with 30 μg of tethered PTH resulted in less bone ingrowth into the defect area. Continued development of this biomaterial delivery system for PTH could lead to improved therapies for treatment of nonunion fractures and critical size bone defects.

Trabecular bone score may indicate chronic kidney disease-mineral and bone disorder (CKD-MBD) phenotypes in hemodialysis patients: a prospective observational study

BACKGROUND

In the general population, the trabecular bone score (TBS) represents the bone microarchitecture and predicts fracture risk independent of bone mineral density (BMD). A few studies reported that TBS is significantly reduced in dialysis patients. Chronic kidney disease-mineral and bone disorder (CKD-MBD) are accompanied by increased fracture risk, cardiovascular morbidity, and mortality. We investigated whether TBS is associated with comorbidity related to CKD-MBD or frailty in hemodialysis patients.

METHODS

In this prospective observational study, TBS was obtained using the TBS iNsight software program (Med-Imaps) with BMD dual energy x-ray absorptiometry (DXA) images (L1-L4) from prevalent hemodialysis patients. A Tilburg frailty indicator was used to evaluate frailty, and hand grip strength and bio-impedance (InBody) were measured. A patient-generated subjective global assessment (PG-SGA) was used for nutritional assessment. The history of cardiovascular events (CVE) and demographic, clinical, laboratory, and biomarker data were collated. We then followed up patients for the occurrence of CKD-MBD related complications.

RESULTS

We enrolled 57 patients in total. The mean age was 56.8 ± 15.9 years (50.9% female). Prevalence of Diabetes mellitus (DM) was 40.4% and CVE was 36.8%. Mean TBS was 1.44 ± 0.10. TBS significantly reduced in the CVE group (1.38 ± 0.08 vs. 1.48 ± 0.10, p <  0.001). Multivariable regression analysis was conducted adjusting for age, sex, dialysis vintage, DM, CVE, albumin, intact parathyroid hormone, fibroblast growth factor 23, handgrip strength, and phosphate binder dose. Age (ß = - 0.030; p = 0.001) and CVE (ß = - 0.055; p = 0.024) were significant predictors of TBS. During the follow up period after TBS measurements (about 20 months), four deaths, seven incident fractures, and six new onset CVE were recorded. Lower TBS was associated with mortality (p = 0.049) or new onset fracture (p = 0.007, by log-rank test).

CONCLUSION

Lower TBS was independently associated with increased age and CVE prevalence in hemodialysis patients. Mortality and fracture incidence were significantly higher in patients with lower TBS values. These findings suggest that TBS may indicate a phenotype of frailty and also a CKD-MBD phenotype reciprocal to CVE.

Changes in Skeletal Microstructure Through Four Continuous Years of rhPTH(1-84) Therapy in Hypoparathyroidism

Bone remodeling is reduced in hypoparathyroidism, resulting in increased areal bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) and abnormal skeletal indices by transiliac bone biopsy. We have now studied skeletal microstructure by high-resolution peripheral quantitative computed tomography (HR-pQCT) through 4 years of treatment with recombinant human PTH(1-84) (rhPTH[1-84]) in 33 patients with hypoparathyroidism (19 with postsurgical disease, 14 idiopathic). We calculated Z-scores for our cohort compared with previously published normative values. We report results at baseline and 1, 2, and 4 years of continuous therapy with rhPTH(1-84). The majority of patients (62%) took rhPTH(1-84) 100 μg every other day for the majority of the 4 years. At 48 months, areal bone density increased at the lumbar spine (+4.9% ± 0.9%) and femoral neck (+2.4% ± 0.9%), with declines at the total hip (-2.3% ± 0.8%) and ultradistal radius (-2.1% ± 0.7%) (p < .05 for all). By HR-pQCT, at the radius site, very similar to the ultradistal DXA site, total volumetric BMD declined from baseline but remained above normative values at 48 months (Z-score + 0.56). Cortical volumetric BMD was lower than normative controls at baseline at the radius and tibia (Z-scores -1.28 and - 1.69, respectively) and further declined at 48 months (-2.13 and - 2.56, respectively). Cortical porosity was higher than normative controls at baseline at the tibia (Z-score + 0.72) and increased through 48 months of therapy at both sites (Z-scores +1.80 and + 1.40, respectively). Failure load declined from baseline at both the radius and tibia, although remained higher than normative controls at 48 months (Z-scores +1.71 and + 1.17, respectively). This is the first report of noninvasive high-resolution imaging in a cohort of hypoparathyroid patients treated with any PTH therapy for this length of time. The results give insights into the effects of long-term rhPTH(1-84) in hypoparathyroidism. © 2020 American Society for Bone and Mineral Research.

Thiol-ene Hydrogels for Local Delivery of PTH for Bone Regeneration in Critical Size defects

Neither allograft nor commercially available bone graft substitutes provide the same quality of bone healing as autograft. Incorporation of bioactive molecules like parathyroid hormone (PTH) within bone graft substitute materials may provide similar, if not better treatment options to grafting. The goal of this work was to develop a biomaterial system for the local delivery of PTH to large bone defects for promoting bone regeneration. PTH was loaded in a thiol-ene hydrogel at several concentrations and polymerized in and around an osteoconductive poly(propylene fumarate) (PPF) scaffold. PTH was shown to be bioactive when released from the hydrogel for up to 21 days. Eighty percent of the PTH was released by day 3 with the remaining 20% released by day 14. Bone healing was quantified in rat critical size femoral defects that were treated with hydrogel/PPF and 0, 1, 3, 10, or 30 µg of PTH. Although complete osseous healing was not observed in all samples in any one treatment group, all samples in the 10 µg PTH group were bridged fully by bone or a combination of bone and cartilage containing hypertrophic chondrocytes and endochondral ossification. Outcome measures indicated improved defect bridging by a combination of bony and cartilaginous tissue in the 10 μg treatment group compared with empty bone defects and defects treated with only hydrogel/PPF (i.e., without PTH). Given the tailorability of the hydrogel, future studies will investigate the effects of prolonged gradual PTH release on bone healing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:536-544, 2020.

Impaired geometry, volumetric density, and microstructure of cortical and trabecular bone assessed by HR-pQCT in both sporadic and MEN1-related primary hyperparathyroidism

This study evaluated bone features of PHPT using HR-pQCT. The results showed both cortical and trabecular bones were significantly impaired in PHPT patients. Male and female PHPT patients suffered similar damages in bone. HR-pQCT indices were not observed to differ in MEN1 and sporadic PHPT patients.

INTRODUCTION

High-resolution peripheral quantitative CT is a novel imaging technique used to separately assess trabecular and cortical bone status of the radius and tibia in vivo. Using HR-pQCT, we aimed to evaluate bone features of primary hyperparathyroidism patients in a Chinese population and reveal similarities and differences in bone features in multiple endocrine neoplasia type 1-related PHPT and sporadic PHPT patients in the Chinese population.

METHODS

A case-control study was designed. In 58 PHPT patients and 58 sex- and age-matched healthy controls, the distal radius and tibia were scanned using HR-pQCT. Areal bone mineral density (aBMD) was also determined in PHPT patients using dual-energy X-ray absorptiometry (DXA).

RESULTS

In comparison with controls, PHPT patients were observed to exhibit reduced volumetric BMD at the cortical and trabecular compartments, thinner cortices, and more widely spaced trabeculae. Significant differences were still observed when comparing data of female and male patients with age-matched controls separately. MHPT patients (n = 11) were found to have lower aBMD Z-scores in the lumbar spine, trochanteric region, and total hip compared with sporadic PHPT patients (n = 47), while no differences were observed in HR-pQCT indices between the two groups. In multiple linear regression models, no significant correlations were identified between PTH and HR-pQCT indices. However, height was found to positively correlate with HR-pQCT-derived trabecular indices at both the radius and tibia.

CONCLUSIONS

PHPT affects geometry, volumetric density, and microstructure in both the cortical and trabecular bones in both male and female Chinese patients. MHPT patients were observed to have reduced aBMD as determined by DXA in the lumbar spine and hip in comparison with sporadic PHPT patients. However, HR-pQCT indices were not observed to differ.

A multi-imaging modality study of bone density, bone structure and the muscle - bone unit in end-stage renal disease

End stage renal disease (ESRD) is associated with sarcopenia and skeletal fragility. The objectives of this cross-sectional study were to (1) characterize body composition, bone mineral density (BMD) and bone structure in hemodialysis patients compared with controls, (2) assess whether DXA areal BMD (aBMD) correlates with peripheral quantitative CT (pQCT) measures of volumetric BMD (vBMD), cortical dimensions and MRI measures of trabecular microarchitecture, and (3) determine the magnitude of bone deficits in ESRD after adjustment for muscle mass. Thirty ESRD participants, ages 25 to 64 years, were compared with 403 controls for DXA and pQCT outcomes and 104 controls for MRI outcomes; results were expressed as race- and sex- specific Z-scores relative to age. DXA appendicular lean mass index (ALMI kg/m2) and total hip, femoral neck, ultradistal and 1/3rd radius aBMD were significantly lower in ESRD, vs. controls (all p < 0.01). pQCT trabecular vBMD (p < 0.01), cortical vBMD (p < 0.001) and cortical thickness (due to a greater endosteal circumference, p < 0.02) and MRI measures of trabecular number, trabecular thickness, and whole bone stiffness were lower (all p < 0.01) in ESRD, vs. controls. ALMI was positively associated with total hip, femoral neck, ultradistal radius and 1/3rd radius aBMD and with tibia cortical thickness (R = 0.46 to 0.64). Adjustment for ALMI significantly attenuated bone deficits at these sites: e.g. mean femoral neck aBMD was 0.79 SD lower in ESRD, compared with controls and this was attenuated to 0.33 with adjustment for ALMI. In multivariate models within the dialysis participants, pQCT trabecular vBMD and cortical area Z-scores were significant and independently (all p < 0.02) associated with DXA femoral neck, total hip, and ultradistal radius aBMD Z-scores. Cortical vBMD (p = 0.01) and cortical area (p < 0.001) Z-scores were significantly and independently associated with 1/3rd radius areal aBMD Z-scores (R2 = 0.62). These data demonstrate that DXA aBMD captures deficits in trabecular and cortical vBMD and cortical area. The strong associations with ALMI, as an index of skeletal muscle, highlight the importance of considering the role of sarcopenia in skeletal fragility in patients with ESRD.

MANAGEMENT OF ENDOCRINE DISEASE: Unmet therapeutic, educational and scientific needs in parathyroid disorders

PARAT, a new European Society of Endocrinology program, aims to identify unmet scientific and educational needs of parathyroid disorders, such as primary hyperparathyroidism (PHPT), including parathyroid cancer (PC), and hypoparathyroidism (HypoPT). The discussions and consensus statements from the first PARAT workshop (September 2018) are reviewed. PHPT has a high prevalence in Western communities, PHPT has a high prevalence in Western communities, yet evidence is sparse concerning the natural history and whether morbidity and long-term outcomes are related to hypercalcemia or plasma PTH concentrations, or both. Cardiovascular mortality and prevalence of low energy fractures are increased, whereas Quality of Life is decreased, although their reversibility by treatment of PHPT has not been convincingly demonstrated. PC is a rare cause of PHPT, with an increasing incidence, and international collaborative studies are required to advance knowledge of the genetic mechanisms, biomarkers for disease activity, and optimal treatments. For example, ~20% of PCs demonstrate high mutational burden, and identifying targetable DNA variations, gene amplifications and gene fusions may facilitate personalized care, such as different forms of immunotherapy or targeted therapy. HypoPT, a designated orphan disease, is associated with a high risk of symptoms and complications. Most cases are secondary to neck surgery. However, there is a need to better understand the relation between disease biomarkers and intellectual function, and to establish the role of PTH in target tissues, as these may facilitate the appropriate use of PTH substitution therapy. Management of parathyroid disorders is challenging, and PARAT has highlighted the need for international transdisciplinary scientific and educational studies in advancing in this field.

Effect of Endogenous Parathyroid Hormone on Bone Geometry and Skeletal Microarchitecture

Parathyroid hormone (PTH) has anabolic or catabolic effects on bones; however, the skeletal effect of endogenous PTH on cortical and trabecular bones is not yet clear. Therefore, we aimed to examine the effects of an excess and a deficiency of endogenous PTH on the lumbar spine trabecular bone score (TBS) and bone geometry using dual-energy X-ray absorptiometry. We retrospectively included 70 patients with primary hyperparathyroidism (PHPT), 26 patients with idiopathic or postoperative hypoparathyroidism (HypoPT), and 96 normal controls matched by age, sex, and body mass index. The bone mineral density (BMD) at the lumbar spine, femur neck, and total hip was higher in the HypoPT, followed by the controls and PHPT group (all P < 0.001). The TBS was significantly decreased in the PHPT group compared to the controls (P = 0.021); however, statistical significance disappeared after adjusting for the lumbar BMD (P = 0.653). There were no significant differences in the TBS between the HypoPT group and controls as well as the PHPT and HypoPT group. As for bone geometry parameters, the cross-sectional area, cross-sectional moment of inertia, and section modulus were higher in the HypoPT, followed by the controls and PHPT group (all P < 0.001); statistical significance remained after adjusting for the total hip BMD. We also observed a significantly increased cortical neck width in the HypoPT group compared to the PHPT group (P = 0.009). The buckling ratio was higher in the PHPT than the HypoPT group and controls (P = 0.018 and P = 0.013, respectively). The present study demonstrated that an excess of endogenous PTH had catabolic effects on both cortical and trabecular bones. Under conditions of endogenous PTH deficiency, the effect on cortical bone was pronounced, but that on trabecular bone was modest.

Innervation is higher above Bone Remodeling Surfaces and in Cortical Pores in Human Bone: Lessons from patients with primary hyperparathyroidism

Mounting evidence from animal studies suggests a role of the nervous system in bone physiology. However, little is known about the nerve fiber localization to human bone compartments and bone surface events. This study reveals the density and distribution of nerves in human bone and the association of nerve profiles to bone remodeling events and vascular structures in iliac crest biopsies isolated from patients diagnosed with primary hyperparathyroidism (PHPT). Bone sections were sequentially double-immunostained for tyrosine hydroxylase (TH), a marker for sympathetic nerves, followed by protein gene product 9.5 (PGP9.5), a pan-neuronal marker, or double-immunostained for either PGP9.5 or TH in combination with CD34, an endothelial marker. In the bone marrow, the nerve profile density was significantly higher above remodeling surfaces as compared to quiescent bone surfaces. Ninety-five percentages of all nerve profiles were associated with vascular structures with the highest association to capillaries and arterioles. Moreover, vasculature with innervation was denser above bone remodeling surfaces. Finally, the nerve profiles density was 5-fold higher in the intracortical pores compared to bone marrow and periosteum. In conclusion, the study shows an anatomical link between innervation and bone remodeling in human bone.

Comparative Effect of rhPTH(1-84) on Bone Mineral Density and Trabecular Bone Score in Hypoparathyroidism and Postmenopausal Osteoporosis

Parathyroid hormone (PTH) (1-84) improves lumbar spine (LS) areal bone mineral density (aBMD) and trabecular bone score (TBS) in hypoparathyroidism over a 2-year treatment period. Studies in osteoporosis have shown that with PTH(1-34) there is a significant increase in LS aBMD and TBS. In this article, we provide new data comparing the effects of the same form of PTH, namely recombinant human PTH, rhPTH(1-84), on aBMD and TBS in hypoparathyroid and osteoporotic patients over an 18-month treatment period. We studied 19 premenopausal (mean age 45.8 ± 11.8 years) and 16 postmenopausal (71 ± 8.4 years) hypoparathyroid women and 38 women with postmenopausal osteoporosis (71 ± 8.3 years). DXA (hologic) at LS, femoral neck, total hip, and distal one-third radius was assessed. Site-matched LS TBS data were extracted from deidentified spine DXA scans using the TBS iNsight software (version 2.1; Medimaps, Geneva, Switzerland). We observed a significant increase in LS aBMD in premenopausal and postmenopausal hypoparathyroid (3 ± 1.1%, p < 0.02 and 3.1 ± 1.4%, p < 0.05, respectively) and osteoporosis (6.2 ± 1.1%, p < 0.0001) patients after 18 months. There was a significant increase (3 ± 1.5%, p = 0.05) in TBS in premenopausal hypoparathyroid patients. A change in TBS was not observed in either postmenopausal group. One-third radius aBMD significantly declined in postmenopausal hypoparathyroid (-3.6 ± 1.1%, p < 0.01) and osteoporosis (-8 ± 1.4%, p < 0.0001) patients. Overall, there was a significantly greater increase in TBS in premenopausal hypoparathyroid than in osteoporosis patients (p < 0.0001) after adjusting for baseline values, age, BMI, and average daily dose of rhPTH(1-84). Comparing only postmenopausal women, the LS aBMD increase was greater in osteoporotic than hypoparathyroid subjects (p < 0.01). Our results demonstrate that rhPTH(1-84) administered for 18 months increases trabecular aBMD in hypoparathyroidism and postmenopausal osteoporosis with greater gains observed in the subjects with osteoporosis. The data suggest different effects of PTH on bone depending on the baseline skeletal structure, skeletal dynamics, compartments, and menopausal status. © 2018 American Society for Bone and Mineral Research.

Classical complications of primary hyperparathyroidism

Traditionally, classical complications of primary hyperparathyroidism are mainly represented by skeletal, kidney and gastrointestinal involvement. The old picture of osteitis fibrosa cystica is no longer commonly seen, at least in the western world. However, new imagining techniques have highlighted deterioration of skeletal tissue in patients with primary hyperparathyroidism not captured by traditional DXA measurement. Concerning the kidney, the most common consequences of excessive parathyroid hormone secretion are hypercalciuria and kidney stones; however, the exact pathogenesis of urinary stone formation is still unknown. The 2013 International Congress on the management of Asymptomatic Primary Hyperparathyroidism, emphasized the role of imaging techniques for early discovery of both skeletal and renal complications in asymptomatic patients. Gastrointestinal manifestations include acid-peptic disease, constipation, pancreatitis and gall stone disease. More studies are needed in this area to find the exact pathophysiological mechanism underlying these manifestations and the effect of parathyroid surgery.

Parathyroid hormone independent hypercalcemia in adults

Parathyroid independent hypercalcemia is characterized by suppressed parathyroid hormone (PTH) in the presence of hypercalcemia. Well known causes and mechanisms are redistribution of calcium from the skeleton, by malignant diseases; inadequately increased intestinal calcium uptake mediated by increased vitamin D activity, and reduced renal elimination due to medications. Frequent and infrequent causes are discussed, and more recent mechanistic models presented in this review. Most hypercalcemic conditions are stable and in equilibrium between the different organs, whereas the utmost severe cases are characterized by rapid rising calcium levels and renal failure, resulting in a vicious circle where a disequilibrium state is developed. Management and treatment depends on the underlying condition and severity. The aim of this review is to discuss non-parathyroid hypercalcemic conditions as seen in the modern clinic, with a focus on areas where recent gain of knowledge has been achieved.

Parathyroid hormone for bone regeneration

Delayed healing and/or non-union occur in approximately 5-10% of the fractures that occur annually in the United States. Segmental bone loss increases the probability of non-union. Though grafting can be an effective treatment for segmental bone loss, autografting is limited for large defects since a limited amount of bone is available for harvest. Parathyroid hormone (PTH) is a key regulator of calcium homeostasis in the body and plays an important role in bone metabolism. Presently PTH is FDA approved for use as an anabolic treatment for osteoporosis. The anabolic effect PTH has on bone has led to research on its use for bone regeneration applications. Numerous studies in animal models have indicated enhanced fracture healing as a result of once daily injections of PTH. Similarly, in a human case study, non-union persisted despite treatment attempts with internal fixation, external fixation, and autograft in combination with BMP-7, until off label use of PTH1-84 was utilized. Use of a biomaterial scaffold to locally deliver PTH to a defect site has also been shown to improve bone formation and healing around dental implants in dogs and drill defects in sheep. Thus, PTH may be used to promote bone regeneration and provide an alternative to autograft and BMP for the treatment of large segmental defects and non-unions. This review briefly summarizes the unmet clinical need for improved bone regeneration techniques and how PTH may help fill that void by both systemically and locally delivered PTH for bone regeneration applications. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2586-2594, 2018.

Continuous infusion of PTH1-34 delayed fracture healing in mice

Hyperparathyroidism, which is increased parathyroid hormone (PTH) levels in the blood, could cause delayed or non-union of bone fractures. But, no study has yet demonstrated the effects of excess continuous PTH exposure, such as that seen in hyperparathyroidism, for fracture healing. Continuous human PTH_1–34 (teriparatide) infusion using an osmotic pump was performed for stabilized tibial fractures in eight-week-old male mice to determine the relative bone healing process compared with saline treatment. Radiographs and micro-computed tomography showed delayed but increased calcified callus formation in the continuous PTH_1–34 infusion group compared with the controls. Histology and quantitative histomorphometry confirmed that continuous PTH_1–34 treatment significantly increased the bone callus area at a later time point after fracture, since delayed endochondral ossification occurred. Gene expression analyses showed that PTH_1–34 resulted in sustained Col2a1 and reduced Col10a1 expression, consistent with delayed maturation of the cartilage tissue during fracture healing. In contrast, continuous PTH_1–34 infusion stimulated the expression of both Bglap and Acp5 through the healing process, in accordance with bone callus formation and remodeling. Mechanical testing showed that continuously administered PTH_1–34 increased the maximum load on Day 21 compared with control mice. We concluded that continuous PTH_1–34 infusion resulted in a delayed fracture healing process due to delayed callus cell maturation but ultimately increased biomechanical properties.

Prevalence and Risk of Vertebral Fractures in Primary Hyperparathyroidism: A Nested Case-Control Study

Prevalence of vertebral fractures (VFx) in primary hyperparathyroidism (PHPT) remains uncertain. We aimed to estimate the prevalence of VFx, investigate potential risk factors associated with VFx, and whether bone mineral density (BMD) differs between PHPT and osteoporotic patients with VFx. Through the Danish National Patient Register, we identified patients diagnosed with PHPT from 2005 to 2015. The diagnosis was verified by reviewing biochemical findings, and X-ray reports were reviewed by two investigators. Osteoporotic patients with VFx were identified from our outpatient clinic and matched on age and sex with PHPT patients with VFx. We identified 792 PHPT patients among whom spine X-ray was available from 588 patients. VFx were present in 122 (21%) patients and were equally frequent among sexes (77% females). Fractured patients were older (70 versus 63 years) and had lower heights (163 versus 166 cm) compared with nonfractured patients (p all < 0.02). After stratification by age groups, the prevalence of VFx differed significantly between sexes (p < 0.01). Ionized calcium and parathyroid hormone did not differ between groups. BMD at total hip and forearm were lower in fractured compared with nonfractured patients (p < 0.03 for both) after adjusting for age, sex, and body mass index (BMI). Compared with osteoporotic patients with VFx (n = 108), BMD at the lumbar spine was higher in PHPT patients with VFx (n = 108) (p < 0.01). This did not change by excluding patients with lumbar VFx (p < 0.01). The severity of PHPT assessed by biochemistry does not seem to be associated with risk of VFx. Compared with osteoporosis, VFx seems to occur at a higher BMD in PHPT. © 2018 American Society for Bone and Mineral Research.

The Deletion of Hdac4 in Mouse Osteoblasts Influences Both Catabolic and Anabolic Effects in Bone

Histone deacetylase 4 (Hdac4) is known to control chondrocyte hypertrophy and bone formation. We have previously shown that parathyroid hormone (PTH) regulates many aspects of Hdac4 function in osteoblastic cells in vitro; however, in vivo confirmation was previously precluded by preweaning lethality of the Hdac4-deficient mice. To analyze the function of Hdac4 in bone in mature animals, we generated mice with osteoblast lineage-specific knockout of Hdac4 (Hdac4^ob-/- ) by crossing transgenic mice expressing Cre recombinase under the control of a 2.3-kb fragment of the Col1a1 promoter with mice bearing loxP-Hdac4. The Hdac4^ob-/- mice survive to adulthood and developed a mild skeletal phenotype. At age 12 weeks, they had short, irregularly shaped and stiff tails due to smaller tail vertebrae, with almost no growth plates. The tibial growth plate zone was also thinned, and Mmp13 and Sost mRNAs were increased in the distal femurs of Hdac4^ob-/- mice. Immunohistochemistry showed that sclerostin was elevated in Hdac4^ob-/- mice, suggesting that Hdac4 inhibits its gene and protein expression. To determine the effect of PTH in these mice, hPTH (1-34) or saline were delivered for 14 days with subcutaneously implanted devices in 8-week-old female Hdac4^ob-/- and wild-type (Hdac4^fl/fl ) mice. Serum CTX, a marker of bone resorption, was increased in Hdac4^ob-/- mice with or without PTH treatment. Tibial cortical bone volume/total volume (BV/TV), cortical thickness (Ct.Th), and relative cortical area (RCA) were decreased in Hdac4^ob-/- mice, but PTH caused no further decrease in Hdac4^ob-/- mice. Tibial trabecular BV/TV and thickness were not changed significantly in Hdac4^ob-/- mice but decreased with PTH treatment. These results indicate that Hdac4 inhibits bone resorption and has anabolic effects via inhibiting Mmp13 and Sost/sclerostin expression. Hdac4 influences cortical bone mass and thickness and knockout of Hdac4 prevents the catabolic effect of PTH in cortical bone. © 2018 American Society for Bone and Mineral Research.

Bone disease in primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a disease of high bone turnover, decreased bone mineral density (BMD) especially at cortical sites, and increased risk of fractures at all skeletal sites. Early diagnosis during the last decades resulted in milder forms of bone involvement. New methods of imaging and validation such as high resolution peripheral quantitative computed tomography and trabecular bone score provide evidence of disturbed bone microarchitecture and explain further the increased risk of fractures at both cortical and trabecular skeletal sites. Parathyroidectomy has a long-term beneficial effect on the skeleton and is probably prudent to refer PHPT patients for surgery in all cases where increased bone fragility is suspected. Bisphosphonates (BPs), mainly alendronate, have been proved as reasonable choices for BMD improvement while cinacalcet has no effect on bone strength in PHPT. Combination of BPs and cinacalcet, is a valid therapeutic approach from a pathophysiological point of view at least in terms of bone health, however, an adequately powered study to prove it is lacking. Adequate dietary calcium intake and vitamin D supplementation is advised as in the general population for the skeletal integrity of PHPT patients albeit with a close monitoring of serum and urinary calcium levels.

Primary hyperparathyroidism

In this Review, we describe the pathogenesis, diagnosis and management of primary hyperparathyroidism (PHPT), with a focus on recent advances in the field. PHPT is a common endocrine disorder that is characterized by hypercalcaemia and elevated or inappropriately normal serum levels of parathyroid hormone. Most often, the presentation of PHPT is asymptomatic in regions of the world where serum levels of calcium are routinely measured. In addition to mild hypercalcaemia, PHPT can manifest with osteoporosis and hypercalciuria as well as with vertebral fractures and nephrolithiasis, both of which can be asymptomatic. Other clinical forms of PHPT, such as classical disease and normocalcaemic PHPT, are less common. Parathyroidectomy, the only curative treatment for PHPT, is recommended in patients with symptoms and those with asymptomatic disease who are at risk of progression or have subclinical evidence of end-organ sequelae. Parathyroidectomy results in an increase in BMD and a reduction in nephrolithiasis. Various medical therapies can increase BMD or reduce serum levels of calcium, but no single drug can do both. More data are needed regarding the neuropsychological manifestations of PHPT and the pathogenetic mechanisms leading to sporadic PHPT, as well as on risk factors for complications of the disorder. Future work that advances our knowledge in these areas will improve the management of the disorder.

Optimal dosing and delivery of parathyroid hormone and its analogues for osteoporosis and hypoparathyroidism - translating the pharmacology

In primary hyperparathyroidism (PHPT), bone loss results from the resorptive effects of excess parathyroid hormone (PTH). Under physiological conditions, PTH has actions that are more targeted to homeostasis and to bone accrual. The predominant action of PTH, either catabolic, anabolic or homeostatic, can be understood in molecular and pharmacokinetic terms. When administered intermittently, PTH increases bone mass, but when present continuously and in excess (e.g. PHPT), bone loss ensues. This dual effect of PTH depends not only on the dosing regimen, continuous or intermittent, but also on how the PTH molecule interacts with various states of its receptor (PTH/PTHrP receptor) influencing downstream signalling pathways differentially. Altering the amino-terminal end of PTH or PTHrP could emphasize the state of the receptor that is linked to an osteoanabolic outcome. This concept led to the development of a PTHrP analogue that interacts preferentially with the transiently linked state of the receptor, emphasizing an osteoanabolic effect. However, designing PTH or PTHrP analogues with prolonged state of binding to the receptor would be expected to be linked to a homeostatic action associated with the tonic secretory state of the parathyroid glands that is advantageous in treating hypoparathyroidism. Ideally, further development of a drug delivery system that mimics the physiological tonic, circadian, and pulsatile profile of PTH would be optimal. This review discusses basic, translational and clinical studies that may well lead to newer approaches to the treatment of osteoporosis as well as to different PTH molecules that could become more advantageous in treating hypoparathyroidism.

Skeletal Microstructure and Estimated Bone Strength Improve Following Parathyroidectomy in Primary Hyperparathyroidism

Context

High-resolution peripheral quantitative computed tomography (HRpQCT) is a noninvasive imaging technology that can provide insight into skeletal microstructure and strength. In asymptomatic primary hyperparathyroidism (PHPT), HRpQCT imaging has demonstrated both decreased cortical and trabecular indices, consistent with evidence for increased fracture risk. There are limited data regarding changes in HRpQCT parameters postparathyroidectomy.

Objective

To evaluate changes in skeletal microstructure by HRpQCT in subjects with PHPT after parathyroidectomy.

Design

We studied 29 subjects with PHPT (21 women, 8 men) with HRpQCT at baseline and 6, 12, 18, and 24 months postparathyroidectomy.

Main Outcome Measures

Volumetric bone mineral density, microarchitectural indices, and finite element analysis at the distal radius and tibia.

Results

At both the radius and tibia, there were significant improvements in total, cortical, and trabecular volumetric bone density as early as 6 months postparathyroidectomy (24-month values for total volumetric bone density, radius: +2.8 ± 4%, tibia: +4.4 ± 4%; P < 0.0001 for both), cortical thickness (radius: +1.1 ± 2%, tibia: +2.0 ± 3%; P < 0.01 for both), and trabecular bone volume (radius: +3.8 ± 5%, tibia: +3.2 ± 4%; P < 0.0001 for both). At both sites, by finite element analysis, stiffness and failure load were improved starting at 6 months postparathyroidectomy (24-month values for failure load, radius: +6.2 ± 6%, tibia: +4.8 ± 7%; P < 0.0001 for both).

Conclusions

These results provide information about skeletal microarchitecture in subjects with PHPT followed through 2 years after parathyroidectomy. Estimated bone strength is improved, consistent with data showing decreased fracture risk postparathyroidectomy.

Catabolic Effects of Human PTH (1-34) on Bone: Requirement of Monocyte Chemoattractant Protein-1 in Murine Model of Hyperparathyroidism

The bone catabolic actions of parathyroid hormone (PTH) are seen in patients with hyperparathyroidism, or with infusion of PTH in rodents. We have previously shown that the chemokine, monocyte chemoattractant protein-1 (MCP-1), is a mediator of PTH’s anabolic effects on bone. To determine its role in PTH’s catabolic effects, we continuously infused female wild-type (WT) and MCP-1^−/− mice with hPTH or vehicle. Microcomputed tomography (µCT) analysis of cortical bone showed that hPTH-infusion induced significant bone loss in WT mice. Further, μCT analysis of trabecular bone revealed that, compared with the vehicle-treated group, the PTH-treated WT mice had reduced trabecular thickness and trabecular number. Notably, MCP-1^−/− mice were protected against PTH-induced cortical and trabecular bone loss as well as from increases in serum CTX (C-terminal crosslinking telopeptide of type I collagen) and TRACP-5b (tartrate-resistant acid phosphatase 5b). In vitro, bone marrow macrophages (BMMs) from MCP-1^−/− and WT mice were cultured with M-CSF, RANKL and/or MCP-1. BMMs from MCP-1^−/− mice showed decreased multinucleated osteoclast formation compared with WT mice. Taken together, our work demonstrates that MCP-1 has a role in PTH’s catabolic effects on bone including monocyte and macrophage recruitment, osteoclast formation, bone resorption, and cortical and trabecular bone loss.

Primary Hyperparathyroidism: Effects on Bone Health

Primary hyperparathyroidism (PHPT) is the most common cause of chronic hypercalcemia. With the advent of routine calcium screening, the classic presentation of renal and osseous symptoms has been largely replaced with mild, asymptomatic disease. In hypercalcemia caused by PHPT, serum parathyroid hormone levels are either high, or inappropriately normal. A single-gland adenoma is responsible for 80% of PHPT cases. Less frequent causes include 4-gland hyperplasia and parathyroid carcinoma. Diminished bone mineral density and nephrolithiasis are the major current clinical sequelae. Parathyroidectomy is the only definitive treatment for PHPT, and in experienced hands, cure rates approach 98%.

Musculoskeletal manifestations of primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) can be associated with a variety of musculoskeletal complaints, which occasionally can be the leading or presenting manifestation. In this paper, we describe the musculoskeletal manifestations observed in patients with primary hyperparathyroidism. Medical record reviews of a select population of 74 patients with primary hyperparathyroidism are seen in a rheumatology practice. Bone manifestations included back pain in 11 patients (15.2 %), generalized bone pain in 7 patients (9.7 %), rib cage/chest pain in 6 (8.3 %), pseudoclubbing in 3, and a giant cell tumor of the mandible in 2 (2.3 %) patients. Articular manifestations such as chondrocalcinosis with or without apatite deposition disease were seen in 13 (17.7 %), arthralgias in 11 (15.2 %), and non-specific synovitis in 7 (9.7 %). Muscle weakness was observed in six patients (8.3 %) and myalgias in three (4.6 %). Less common manifestations such as Achilles tendon rupture, Jaccoud-like arthropathy, sacral insufficiency fracture, arthritis associated with fever of unknown origin (FUO), meningitis, cervical cord compression, and persistent headache were observed in single patients. Musculoskeletal findings are still a frequent and important presentation in patients with primary hyperparathyroidism seen in rheumatology practice. Some of these manifestations can be quite unusual and may represent diagnostic dilemmas to the practicing rheumatologist and/or endocrinologist.

An update on bone imaging and markers in chronic kidney disease

Bone disorders in chronic kidney disease (CKD) are associated with heightened risks of fractures, vascular calcification, poor quality of life and mortality compared to the general population. However, diagnosis and management of these disorders in CKD are complex and appreciably limited by current diagnostic modalities. Areas covered: Bone histomorphometry remains the gold standard for diagnosis but is not widely utilised and lacks feasibility as a monitoring tool. In practice, non-invasive imaging and biochemical markers are preferred to guide therapeutic decisions. Expert commentary: This review aims to summarize the risk factors for, and spectrum of bone disease in CKD, as well as appraise the clinical utility of dual energy X-ray densitometry, peripheral quantitative computed tomography, high-resolution peripheral quantitative computed tomography, and bone turnover markers.

Bone loss in chronic kidney disease: Quantity or quality?

Chronic kidney disease (CKD) patients experience bone loss and fracture because of a specific CKD-related systemic disorder known as CKD-mineral bone disorder (CKD-MBD). The bone turnover, mineralization, and volume (TMV) system describes the morphological bone lesions in renal osteodystrophy related to CKD-MBD. Bone turnover and bone volume are defined as high, normal, or low, and bone mineralization is classified as normal or abnormal. All types of bone histology related to TMV are responsible for both bone quantity and bone quality losses in CKD patients. This review focuses on current bone quantity and bone quality losses in CKD patients and finally discusses potential therapeutic measures.

TRABECULAR BONE SCORE IN PATIENTS WITH NORMOCALCEMIC HYPERPARATHYROIDISM

OBJECTIVE

The effects of normocalcemic hyperparathyroidism (NHPT) on bone remain unclear. The objective of this study was to evaluate differences in the trabecular bone score (TBS) of NHPT patients and asymptomatic hypercalcemic hyperparathyroidism (HHPT) patients.

METHODS

We performed a prospective study that enrolled consecutive patients with asymptomatic hyperparathyroidism (NHPT and HHPT) with a follow-up ≥1 year at the University Hospital of Valladolid, Spain. Metabolic phosphocalcium plasma and urine parameters were evaluated in ≥2 determinations during follow-up to classify patients as NHPT patients or asymptomatic HHPT patients. A control group was enrolled during the same period. TBS and bone mineral density (BMD) were evaluated.

RESULTS

Thirty-nine patients with asymptomatic HPT (24 with NHPT and 15 with HHPT) and 24 controls were recruited. NHPT patients and HHPT patients had a similar mean age, vitamin D level, TBS, and areal BMD (all sites). Compared to controls, symptomatic HPT patients had significantly higher parathyroid hormone (PTH) and calcium levels and significantly lower TBS and areal BMD at all sites (all P<.05). A significant negative relationship between TBS and PTH was found in asymptomatic HPT patients (r = -0.320, P = .043), which remained significant after adjustment for age, sex, and body mass index.

CONCLUSION

There was no difference in the TBS between NHPT and HHPT patients. However, there was a reduction in the TBS of patients with asymptomatic HPT that was related to PTH levels but had no repercussion on bone mass. Higher levels of PTH seem to be responsible for this alteration in microarchitecture texture.

ABBREVIATIONS

aBMD = areal bone mineral density BMD = bone mineral density BMI = body mass index DXA = dual-energy X-ray absorptiometry HHPT = hypercalcemic hyperparathyroidism HPT = hyperparathyroidism HR-MRI = high-resolution magnetic resonance HR-pQcT = high-resolution peripheral quantitative computed tomography NHPT = normocalcemic hyper-parathyroidism PTH = parathyroid hormone TBS = trabecular bone score 25vitD = 25-hydroxyvitamin D.

Noninvasive Assessment of Skeletal Microstructure and Estimated Bone Strength in Hypoparathyroidism

In hypoparathyroidism, areal bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) is above average, and skeletal indices by bone biopsy are abnormal. We used high-resolution peripheral quantitative computed tomography (HRpQCT) and finite element analyses (FEA) to further investigate skeletal microstructure and estimated bone strength. We studied 60 hypoparathyroid subjects on conventional therapy using DXA, HRpQCT, and FEA of the distal radius and tibia compared with normative controls from the Canadian Multicentre Osteoporosis Study. In hypoparathyroid women and men, areal BMD was above average at the lumbar spine and hip sites by DXA; radial BMD was also above average in hypoparathyroid women. Using HRpQCT, cortical volumetric BMD was increased in the hypoparathyroid cohort compared with controls at both the radius and tibia. Cortical porosity was reduced at both sites in pre- and postmenopausal women and at the tibia in young men with a downward trend at the radius in men. At the tibia, trabecular number was increased in premenopausal women and men and trabecular thickness was lower in women. Ultimate stress and failure load at both sites for the hypoparathyroid subjects were similar to controls. Using a linear regression model, at both radius and tibia, each increment in age decreased ultimate stress and failure load, whereas each increment in duration of hypoparathyroidism increased these same indices. These results provide additional evidence for the critical role of parathyroid hormone in regulating skeletal microstructure. Longer disease duration may mitigate the adverse effects of age on estimated bone strength in hypoparathyroidism.

Treatment with intermittent PTH increases Wnt10b production by T cells in osteoporotic patients

We evaluated the effect of parathyroid hormone (PTH) on Wnt10b production by immune system cells in humans. We showed that bone anabolic effect of intermittent PTH treatment may be amplified by T cells through increased production of Wnt10b. Chronic increase in PTH as in primary hyperparathyroidism does not increase Wnt10b expression.

INTRODUCTION

The aim of this study is to assess the effect of PTH on Wnt10b production by immune system cells in humans. We assessed both the effect of intermittent PTH administration (iPTH) and of chronic PTH hypersecretion in primary hyperparathyroidism (PHP).

METHODS

Eighty-two women affected by post-menopausal osteoporosis were randomly assigned to treatment with calcium and vitamin D alone (22) or plus 1-84 PTH (42), or intravenous ibandronate (18). Wnt10b production by unfractioned blood nucleated cells and by T, B cells and monocytes was assessed by real-time RT-PCR and ELISA at baseline, 3, 6, 12 and 18 months of treatment. The effect of chronic elevation of PTH was evaluated in 20 patients affected by PHP at diagnosis and after surgical removal of parathyroid adenoma. WNT10b from both osteoporotic and PHP patients was compared to healthy subjects matched for age and sex.

RESULTS

iPTH increases Wnt10b production by T cells, whereas PHP does not. After surgical restoration of normal parathyroid function, WNT10b decreases, although it is still comparable with healthy subjects' level. Thus, chronic elevation of PTH does not significantly increase WNT10b production as respect to control.

CONCLUSIONS

This is the first work showing the effect of both intermittent and chronic PTH increase on Wnt10b production by immune system cells. We suggest that, in humans, T cells amplified the anabolic effect of PTH on bone, by increasing Wnt10b production, which stimulates osteoblast activity.

The calcium-sensing receptor in bone--mechanistic and therapeutic insights

The extracellular calcium-sensing receptor, CaSR, is a member of the G protein-coupled receptor superfamily and has a critical role in modulating Ca(2+) homeostasis via its role in the parathyroid glands and kidneys. New evidence suggests that CaSR expression in cartilage and bone also directly regulates skeletal homeostasis. This Review discusses the role of CaSR in chondrocytes, through which CaSR contributes to the development of the cartilaginous growth plate, as well as in osteoblasts and osteoclasts, through which CaSR has effects on skeletal development and bone turnover in young and mature animals. The interaction of skeletal CaSR activation with parathyroid hormone (PTH), which is secreted by the parathyroid gland, can lead to net bone formation in trabecular bone or net bone resorption in cortical bone. Allosteric modulators of CaSR are beneficial in some clinical conditions, with effects that are mediated by the ability of these agents to alter levels of PTH and improve Ca(2+) homeostasis. However, further insights into the action of CaSR in bone cells might lead to CaSR-based drugs that maximize not only the effects of the receptor on the parathyroid glands and kidneys but also on bone.

Stk11 (Lkb1) deletion in the osteoblast lineage leads to high bone turnover, increased trabecular bone density and cortical porosity

The mTOR pathway couples energy homeostasis to growth, division and survival of the cell. Stk11/Lkb1 is a critical serine-threonine protein kinase in the inhibition of mTOR pathway action. In the mammalian skeleton, Stk11 regulates the transition between immature and hypertrophic chondrocytes. Here, we have focused on the action of Stk11in the osteoblast lineage through osteoblast specific-removal of Stk11 activity. In the mouse model system, specification and primary organization of the neonatal boney skeleton is independent of Stk11. However, histological, molecular and micro-CT analysis revealed a marked perturbation of normal bone development evident in the immediate post-natal period. Cortical bone was unusually porous displaying a high rate of turnover with new trabeculae forming in the endosteal space. Trabecular bone also showed enhanced turnover and marked increase in the density of trabeculae and number of osteoclasts. Though mutants showed an expansion of bone volume and trabecular number, their bone matrix comprised large amounts of osteoid and irregularly deposited woven bone highlighted by diffuse fluorochrome labeling. Additionally, we observed an increase in fibroblast-like cells associated with trabecular bone in Stk11 mutants. Stk11 down-regulates mTORC1 activity through control of upstream modulators of the AMP kinase family: an increase in the levels of the phosphorylated ribosomal protein S6, a target of mTORC1-mediated kinase activity, on osteoblast removal of Stk11 suggests deregulated mTORC1 activity contributes to the osteoblast phenotype. These data demonstrate Stk11 activity within osteoblasts is critical for the development of normally structured bone regulating directly the number and coordinated actions of osteoblasts, and indirectly osteoclast number.

Bone disease in primary hyperparathyroidism

Bone disease in severe primary hyperparathyroidism (PHPT) is described classically as osteitis fibrosa cystica (OFC). Bone pain, skeletal deformities and pathological fractures are features of OFC. Bone mineral density is usually extremely low in OFC, but it is reversible after surgical cure. The signs and symptoms of severe bone disease include bone pain, pathologic fractures, proximal muscle weakness with hyperreflexia. Bone involvement is typically characterized as salt-and-pepper appearance in the skull, bone erosions and bone resorption of the phalanges, brown tumors and cysts. In the radiography, diffuse demineralization is observed, along with pathological fractures, particularly in the long bones of the extremities. In severe, symptomatic PHPT, marked elevation of the serum calcium and PTH concentrations are seen and renal involvement is manifested by nephrolithiasis and nephrocalcinosis. A new technology, recently approved for clinical use in the United States and Europe, is likely to become more widely available because it is an adaptation of the lumbar spine DXA image. Trabecular bone score (TBS) is a gray-level textural analysis that provides an indirect index of trabecular microarchitecture. Newer technologies, such as high-resolution peripheral quantitative computed tomography (HR-pQCT), have provided further understanding of the microstructural skeletal features in PHPT.

Consequences of irradiation on bone and marrow phenotypes, and its relation to disruption of hematopoietic precursors

The rising levels of radiation exposure, specifically for medical treatments and accidental exposures, have added great concern for the long term risks of bone fractures. Both the bone marrow and bone architecture are devastated following radiation exposure. Even sub-lethal doses cause a deficit to the bone marrow microenvironment, including a decline in hematopoietic cells, and this deficit occurs in a dose dependent fashion. Certain cell phenotypes though are more susceptible to radiation damage, with mesenchymal stem cells being more resilient than the hematopoietic stem cells. The decline in total bone marrow hematopoietic cells is accompanied with elevated adipocytes into the marrow cavity, thereby inhibiting hematopoiesis and recovery of the bone marrow microenvironment. Poor bone marrow is also associated with a decline in bone architectural quality. Therefore, the ability to maintain the bone marrow microenvironment would hinder much of the trabecular bone loss caused by radiation exposure, ultimately decreasing some comorbidities in patients exposed to radiation.

Vitamin D supplementation after parathyroidectomy: effect on bone mineral density-a randomized double-blind study

Patients with primary hyperparathyroidism (PHPT) have higher bone turnover, lower bone mineral density (BMD), and an increased risk of fractures. They also have a high incidence of low vitamin D levels (25-OH-vitamin D <50 nmol/L) that could worsen the negative effect on the bone. In this double-blinded clinical trial, 150 patients with PHPT were randomized, after successful parathyroidectomy (PTX), to 1-year daily treatment with either cholecalciferol 1600 IU and calcium carbonate 1000 mg (D+) or calcium carbonate alone (D-). BMD was measured in the lumbar spine, femoral neck, total hip, distal and 33% radius using dual-energy X-ray absorptiometry (DXA) before surgery and after 1 year of study medication. Median age was 60 (range 30-80) years and there were 119 (79%) women and 31 (21%) men; 76% had 25-OH-D <50 nmol/L before PTX and 50% had persistent elevated parathyroid hormone (PTH) 6 weeks after PTX. A similar increase in BMD in the lumbar spine, femoral neck, and total hip was observed in both groups (D+ : 3.6%, 3.2%, and 2.7%, p<0.001, respectively; and D-: 3.0%, 2.3%, and 2.1%, respectively, p<0.001). Patients with vitamin D supplementation also increased their BMD in distal radius (median 2.0%; interquartile range, -1.7% to 5.4%; p=0.013). The changes in BMD, especially in the hips, were correlated to the baseline concentrations of PTH, ionized calcium, and bone markers (p<0.001). A benefit from vitamin D substitution was observed among patients with a persistent postoperative PTH elevation, who also improved their BMD at 33% radius and radius ultradistal (p<0.05). In conclusion, except for a minor improvement of radius BMD, our data show no beneficial effect on BMD or bone turnover markers of vitamin D supplementation after PTX. Preoperative PTH seems to have the strongest association with improvement in BMD.

Bone Involvement in Primary Hyperparathyroidism and Changes After Parathyroidectomy

Parathyroid hormone (PTH) is produced and secreted by the parathyroid glands and has primary effects on kidney and bone. During the pathological growth of one or more parathyroid glands, the plasma level of PTH increases and causes primary hyperparathyroidism (PHPT). This disease is normally characterised by hyperparathyroid hypercalcaemia. In PHPT a continuously elevated PTH stimulates the kidney and bone causing a condition with high bone turnover, elevated plasma calcium and increased fracture risk. If bone resorption is not followed by a balanced formation of new bone, irreversible bone loss may occur in these patients. Medical treatment can help to minimise the loss of bone but the cure of PHPT is by parathyroidectomy. After operation, bone mineral density increases during the return to normal bone metabolism. Supplementation with calcium and vitamin D after operation may improve the normalisation to normal bone metabolism with a secondary reduction in fracture risk.

Prevalence of primary hyperparathyroidism among patients with low bone mass

PURPOSE

Accelerated rate of bone turnover and increased resorption due to primary hyperparathyroidism (PHPT) result in osteopenia and an increase in the fracture risk. However, there are no data about the relative frequency of the PHPT in the subpopulation with the low bone mass. The aim of the study was to evaluate the diagnostic power of the bone densitometry in diagnosis of PHPT.

PATIENTS AND METHODS

Material consisted of 4016 new patients: 2504 women and 1512 men. Bone mineral density (BMD) in the L2 - L4 vertebra and femoral neck was measured by DEXA (LUNAR - DPX or LUNAR - EXPERT, Lunar Radiation Corp., USA). All the patients with BMD Z-score below -2.0 SD (according to the sex and age) were the subjects of further diagnostic procedures. The serum calcium and intact PTH level as well as 24-hours urine excretion was measured.

RESULTS

In 451 (331 women and 120 men) out of the total 4016 patients, the measured BMD Z-scores were below -2.0 SD. Out of these 451 patients, 52 were diagnosed with PHPT. In 41 patients, diagnosis of PHPT was based on elevated serum intact PTH in the face of overt hypercalcemia. The remaining 11 normocalcemic patients with elevated PTH and coexisting vitamin D deficiency, will become hypercalcemic after vitamin D replacement.

CONCLUSIONS

In the large cohort of unselected patients who presented for bone densitometry, a very high (11.5%) prevalence of PHPT was found among subjects with low bone mass (BMD Z-score less than -2.0 SD). Presented results confirm the importance of the BMD measurements in the screening of the disease.

The effect of endogenous parathyroid hormone in iliac bone structure and turnover in healthy postmenopausal women

Little is known about the effect of endogenous parathyroid hormone (PTH) on the skeleton in postmenopausal women without hyperparathyroidism. In this study, the effects of PTH on bone were investigated in iliac crest biopsies obtained from 37 healthy white postmenopausal women aged 50-73 years. The results showed that neither cancellous nor cortical bone structure changed with serum PTH levels. In cancellous bone, bone formation (wall thickness, osteoid surface, osteoblast surface, mineralizing surface, and mineral apposition rate) and turnover (bone formation rate at the surface, volume levels, and activation frequency) variables increased with increasing serum PTH levels (all p < 0.05) in univariate analysis. Multiple linear regressions, adjusted for serum 25-OHD, calcium, alkaline phosphatase, age, and BMI, showed that serum PTH level was independently associated with wall thickness, osteoid surface, osteoblast surface, mineralizing surface, and bone formation rate (all p < 0.05). In cortical bone, no histomorphometric variable was correlated with PTH levels. On the endosteal surface, some of the bone formation (osteoid surface, osteoblast surface, mineralizing surface) and turnover (bone formation rate at the bone surface levels and activation frequency) variables were positively correlated with PTH levels (all p < 0.05). None of these variables could be independently predicted by PTH status. We conclude that in healthy postmenopausal women endogenous PTH has a positive effect on bone formation on the cancellous surface. The effects of PTH on the endosteal surface are probably confounded by other factors.

Rapid cortical bone loss in patients with chronic kidney disease

Chronic kidney disease (CKD) patients may have high rates of bone loss and fractures, but microarchitectural and biochemical mechanisms of bone loss in CKD patients have not been fully described. In this longitudinal study of 53 patients with CKD Stages 2 to 5D, we used dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HRpQCT), and biochemical markers of bone metabolism to elucidate effects of CKD on the skeleton. Median follow-up was 1.5 years (range 0.9 to 4.3 years); bone changes were annualized and compared with baseline. By DXA, there were significant declines in areal bone mineral density (BMD) of the total hip and ultradistal radius: -1.3% (95% confidence interval [CI] -2.1 to -0.6) and -2.4% (95% CI -4.0 to -0.9), respectively. By HRpQCT at the distal radius, there were significant declines in cortical area, density, and thickness and increases in porosity: -2.9% (95% CI -3.7 to -2.2), -1.3% (95% CI -1.6 to -0.6), -2.8% (95% CI -3.6 to -1.9), and +4.2% (95% CI 2.0 to 6.4), respectively. Radius trabecular area increased significantly: +0.4% (95% CI 0.2 to 0.6), without significant changes in trabecular density or microarchitecture. Elevated time-averaged levels of parathyroid hormone (PTH) and bone turnover markers predicted cortical deterioration. Higher levels of serum 25-hydroxyvitamin D predicted decreases in trabecular network heterogeneity. These data suggest that significant cortical loss occurs with CKD, which is mediated by hyperparathyroidism and elevated turnover. Future investigations are required to determine whether these cortical losses can be attenuated by treatments that reduce PTH levels and remodeling rates.

Primary hyperparathyroidism is associated with abnormal cortical and trabecular microstructure and reduced bone stiffness in postmenopausal women

Typically, in the milder form of primary hyperparathyroidism (PHPT), now seen in most countries, bone density by dual-energy X-ray absorptiometry (DXA) and detailed analyses of iliac crest bone biopsies by histomorphometry and micro-computed tomography (µCT) show detrimental effects in cortical bone, whereas the trabecular site (lumbar spine by DXA) and the trabecular compartment (by bone biopsy) appear to be relatively well preserved. Despite these findings, fracture risk at both vertebral and nonvertebral sites is increased in PHPT. Emerging technologies, such as high-resolution peripheral quantitative computed tomography (HRpQCT), may provide additional insight into microstructural features at sites such as the forearm and tibia that have heretofore not been easily accessible. Using HRpQCT, we determined cortical and trabecular microstructure at the radius and tibia in 51 postmenopausal women with PHPT and 120 controls. Individual trabecula segmentation (ITS) and micro-finite element (µFE) analyses of the HRpQCT images were also performed to further understand how the abnormalities seen by HRpQCT might translate into effects on bone strength. 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. These results provide evidence that in PHPT, microstructural abnormalities are pervasive and not limited to the cortical compartment, which may help to account for increased global fracture risk in PHPT.