Three dimensional cancellous bone structure in hypoparathyroidism

Skeletal health status among patients with chronic hypoparathyroidism: results from the Canadian National Hypoparathyroidism Registry (CNHR)

In the CNHR study, 35% of postmenopausal women had osteoporosis by BMD or fragility fracture, and 4% had both. Three men ≥ 50 had osteoporosis by BMD or fragility fracture (33.3%; n = 3/9). This suggests that close follow-up of skeletal health is necessary in postmenopausal women, and men ≥ 50 with chronic HypoPT.

PURPOSE

Chronic hypoparathyroidism (HypoPT) has been associated with decreased bone turnover and abnormalities in bone mineral density (BMD), microarchitecture, and strength. Current guidelines do not recommend systematic evaluation of skeletal health in patients with chronic HypoPT. Our study assessed skeletal health in pre- and postmenopausal women with chronic HypoPT and adult men.

METHODS

This prospective study enrolled adults with chronic HypoPT from the Canadian National Hypoparathyroidism Registry. Clinical characteristics, bone fractures, biochemistry, and serum bone biomarkers were assessed at baseline. Skeletal health evaluation included assessments of fragility fractures, BMD at lumbar spine (LS), femoral neck (FN), total hip (TH), 1/3 radial sites, trabecular bone score (TBS), and bone biomarkers.

RESULTS

We present the baseline data of the patients enrolled in the registry. We analyzed a total of 101 patients: 18 men, 35 premenopausal, and 48 postmenopausal women. The mean (SD) age at the onset of HypoPT was 40.7 (16.8) years, and the average disease duration was 11.2 (8.6) years. The most common etiology was postsurgical (74.3% vs. 25.7% non-surgical). Most patients received calcium supplements (89%) and active vitamin D (80%) at baseline. No fragility fractures or low BMD were reported in premenopausal women. However, BMD at LS, FN, TH, and TBS were significantly lower in postmenopausal compared to premenopausal women.

CONCLUSIONS

Overall, 35% of postmenopausal women had osteoporosis by BMD or prior fragility fracture, and 4% had both. Three men ≥ 50 years had osteoporosis by BMD or fragility fracture (33.3%; n = 3/9). This study suggests that close follow-up of skeletal health is necessary in postmenopausal women with chronic HypoPT and men ≥ 50 years.

Styloid process phenotype and atheromatous plaque: Radiographic and bone density assessment in parathyroid disease

Purpose

This study aimed to assess the styloid process (TBSP) phenotype and to identify suggestive images of calcified atheromatous plaques (CAP) in panoramic radiographs of patients with primary hyperparathyroidism (PHPT) and post-surgical hypoparathyroidism (hypoPT). Additionally, it aimed to analyze the association between the bone mineral status of patients with parathyroid diseases and the radiographic findings.

Material and methods

A cross-sectional case-control study was conducted with individuals diagnosed with PHPT (n = 25) and post-surgical hypoPT (n = 25). A control group (n = 50) comprised individuals without parathyroid gland disorders. Panoramic radiographs were utilized for both quantitative (length) and qualitative (mineralization patterns) evaluation of the TBSP, as well as for assessing the prevalence of CAP.

Results

The frequency of TBSP exceeding 30 mm was significantly higher in the PHPT and post-surgical hypoPT groups compared to the control group. CAP occurred more frequently in the PHPT group. Cases of low bone mineral density (BMD) were associated with PHPT. In the PHPT group, low BMD was linked to an increased average TBSP length (p = 0.025) and a higher frequency of elongated TBSP (p = 0.022). Multivariate analysis revealed an inverse relationship between the T-score of the femoral neck and TBSP length in the PHPT group (p = 0.028).

Conclusions

Compared to the control group, individuals with PHPT and post-surgical hypoPT showed distinct imaging findings related to TBSP and CAP. Individuals with PHPT and low BMD showed a higher frequency of elongated TBSP.

An Open-label Phase 2 Study of Eneboparatide, a Novel PTH Receptor 1 Agonist, in Hypoparathyroidism

CONTEXT

Hypoparathyroidism is a rare disorder characterized by a deficiency in PTH resulting in hypocalcemia, hyperphosphatemia, and hypercalciuria. Eneboparatide is an investigational peptide agonist of the PTH1 receptor for the treatment of chronic hypoparathyroidism (HP).

OBJECTIVE

To evaluate the efficacy, safety, and tolerability of eneboparatide in HP patients.

DESIGN

Open-label, phase 2 study.

PARTICIPANTS

Twenty-eight patients (21 women, 7 men), mean age (range): 58 years (28-72), with HP were enrolled into 2 consecutive cohorts (C1, n = 12 and C2, n = 16).

INTERVENTION

Following an optimization period, daily subcutaneous injections of eneboparatide were administered for 3 months at a 20 µg/day (C1) or 10 µg/day (C2) starting dose. Conventional therapy was progressively removed, and eneboparatide could be titrated up to 60 µg (C1) or 80 µg (C2).

MAIN OUTCOMES

Proportion of patients achieving independence from conventional therapy, albumin-adjusted serum calcium (ADsCa), 24-h urine calcium (uCa), serum bone turnover markers (serum carboxy-terminal telopeptide of type I collagen and procollagen 1 intact N-terminal propeptide), bone mineral density (BMD), and adverse events (AEs).

RESULTS

After 3 months, ≥ 88% of patients achieved independence from conventional therapy while mean ADsCa was maintained within target range (7.8-9 mg/dL). Eneboparatide induced a rapid and sustained reduction of mean 24-hour uCa, even among patients with hypercalciuria. Bone turnover markers slightly increased, and BMD remained unchanged, consistent with progressive resumption of physiologic bone turnover. Eneboparatide was well tolerated with no serious AEs.

CONCLUSION

Eneboparatide allowed independence from conventional therapy and maintenance of serum calcium within a target range while normalizing uCa excretion and producing a balanced resumption of bone turnover.

Update on the clinical use of trabecular bone score (TBS) in the management of osteoporosis: results of an expert group meeting organized by the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO), and the International Osteoporosis Foundation (IOF) under the auspices of WHO Collaborating Center for Epidemiology of Musculoskeletal Health and Aging

PURPOSE

Trabecular bone score (TBS) is a grey-level textural measurement acquired from dual-energy X-ray absorptiometry lumbar spine images and is a validated index of bone microarchitecture. In 2015, a Working Group of the European Society on Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) published a review of the TBS literature, concluding that TBS predicts hip and major osteoporotic fracture, at least partly independent of bone mineral density (BMD) and clinical risk factors. It was also concluded that TBS is potentially amenable to change as a result of pharmacological therapy. Further evidence on the utility of TBS has since accumulated in both primary and secondary osteoporosis, and the introduction of FRAX and BMD T-score adjustment for TBS has accelerated adoption. This position paper therefore presents a review of the updated scientific literature and provides expert consensus statements and corresponding operational guidelines for the use of TBS.

METHODS

An Expert Working Group was convened by the ESCEO and a systematic review of the evidence undertaken, with defined search strategies for four key topics with respect to the potential use of TBS: (1) fracture prediction in men and women; (2) initiating and monitoring treatment in postmenopausal osteoporosis; (3) fracture prediction in secondary osteoporosis; and (4) treatment monitoring in secondary osteoporosis. Statements to guide the clinical use of TBS were derived from the review and graded by consensus using the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) approach.

RESULTS

A total of 96 articles were reviewed and included data on the use of TBS for fracture prediction in men and women, from over 20 countries. The updated evidence shows that TBS enhances fracture risk prediction in both primary and secondary osteoporosis, and can, when taken with BMD and clinical risk factors, inform treatment initiation and the choice of antiosteoporosis treatment. Evidence also indicates that TBS provides useful adjunctive information in monitoring treatment with long-term denosumab and anabolic agents. All expert consensus statements were voted as strongly recommended.

CONCLUSION

The addition of TBS assessment to FRAX and/or BMD enhances fracture risk prediction in primary and secondary osteoporosis, adding useful information for treatment decision-making and monitoring. The expert consensus statements provided in this paper can be used to guide the integration of TBS in clinical practice for the assessment and management of osteoporosis. An example of an operational approach is provided in the appendix. This position paper presents an up-to-date review of the evidence base, synthesised through expert consensus statements, which informs the implementation of Trabecular Bone Score in clinical practice.

Bone Tissue Evaluation Indicates Abnormal Mineralization in Patients with Autoimmune Polyendocrine Syndrome Type I: Report on Three Cases

Autoimmune polyendocrine syndrome type-1 (APS1) is characterized by autoimmune manifestations affecting different organs from early childhood on. Immunological abnormalities, the resulting endocrinopathies, and their treatments may compromise bone health. For the first time in APS1, we analyzed transiliac bone biopsy samples by bone histomorphometry and quantitative backscattered electron imaging in three adult patients (female P1, 38 years; male P2, 47 years; male P3, 25 years). All had biallelic mutations in the autoimmune regulator gene and in addition to endocrinopathies, also significant bone fragility. Histomorphometry showed bone volume in the lower normal range for P1 (BV/TV, - 0.98 SD) and P3 (- 1.34 SD), mainly due to reduced trabecular thickness (TbTh, - 3.63 and - 2.87 SD). In P1, osteoid surface was low (OS/BS, - 0.96 SD); active osteoblasts and double labeling were seen only on cortical bone. P3 showed a largely increased bone turnover rate (BFR/BV, + 4.53 SD) and increased mineralization lag time (Mlt, + 3.40 SD). Increased osteoid surface (OS/BS, + 2.03 and + 4.71 SD for P2 and P3) together with a large proportion of lowly mineralized bone area (Trab CaLow, + 2.22 and + 9.81 SD for P2 and P3) and focal mineralization defects were consistent with abnormal mineralization. In all patients, the density and area of osteocyte lacunae in cortical and trabecular bone were similar to healthy adults. The bone tissue characteristics were variable and included decreased trabecular thickness, increased amount of osteoid, and abnormal mineralization which are likely to contribute to bone fragility in patients with APS1.

Etiology and Pathophysiology of Hypoparathyroidism: A Narrative Review

The approach utilized a systematic review of the medical literature executed with specifically designed criteria that focused on the etiologies and pathogenesis of hypoparathyroidism. Enhanced attention by endocrine surgeons to new knowledge about parathyroid gland viability are reviewed along with the role of intraoperative parathyroid hormone (ioPTH) monitoring during and after neck surgery. Nonsurgical etiologies account for a significant proportion of cases of hypoparathyroidism (~25%), and among them, genetic etiologies are key. Given the pervasive nature of PTH deficiency across multiple organ systems, a detailed review of the skeletal, renal, neuromuscular, and ocular complications is provided. The burden of illness on affected patients and their caregivers contributes to reduced quality of life and social costs for this chronic endocrinopathy. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Evaluation and Management of Hypoparathyroidism Summary Statement and Guidelines from the Second International Workshop

This clinical practice guideline addresses the prevention, diagnosis, and management of hypoparathyroidism (HypoPT) and provides evidence-based recommendations. The HypoPT task forces included four teams with a total of 50 international experts including representatives from the sponsoring societies. A methodologist (GG) and his team supported the taskforces and conducted the systematic reviews. A formal process following the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methodology and the systematic reviews provided the structure for seven of the guideline recommendations. The task force used a less structured approach based on narrative reviews for 20 non-GRADEd recommendations. Clinicians may consider postsurgical HypoPT permanent if it persists for >12 months after surgery. To predict which patients will not develop permanent postsurgical HypoPT, we recommend evaluating serum PTH within 12 to 24 hours post total thyroidectomy (strong recommendation, moderate quality evidence). PTH > 10 pg/mL (1.05 pmol/L) virtually excludes long-term HypoPT. In individuals with nonsurgical HypoPT, genetic testing may be helpful in the presence of a positive family history of nonsurgical HypoPT, in the presence of syndromic features, or in individuals younger than 40 years. HypoPT can be associated with complications, including nephrocalcinosis, nephrolithiasis, renal insufficiency, cataracts, seizures, cardiac arrhythmias, ischemic heart disease, depression, and an increased risk of infection. Minimizing complications of HypoPT requires careful evaluation and close monitoring of laboratory indices. In patients with chronic HypoPT, the panel suggests conventional therapy with calcium and active vitamin D metabolites as first-line therapy (weak recommendation, low-quality evidence). When conventional therapy is deemed unsatisfactory, the panel considers the use of PTH. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

The Russian Registry of Chronic Hypoparathyroidism

INTRODUCTION

Chronic hypoparathyroidism is a relatively rare disease associated with multicomponent medical therapy and various complications. The analysis of large databases of patients with chronic hypoparathyroidism is a necessary tool to enhance quality of medical care, as well as to determine the optimal clinical and therapeutic approaches, and prognostic markers of the disease.

THE AIM

of this study is to estimate the clinical and biochemical profile, long-term complications, medical therapy and disease control of the patients with chronic postsurgical and non-surgical hypoparathyroidism.

MATERIALS AND METHODS

the cross-sectional, observational, continuous study was based on the Russian Registry of patients with hypoparathyroidism. 544 patients from 63 regions of the Russian Federation were included in this study.

RESULTS

The majority of cases had postsurgical etiology (88.4%). Postsurgical hypoparathyroidism prevailed in females (р<0.001). About a half of patients had blood calcium and phosphorus targets, 56 and 52% respectively. Nephrolithiasis was confirmed in 32.5%, nephrocalcinosis - in 12.3% of cases. The risk of nephrocalcinosis/nephrolithiasis increased by 1.85 times with disease duration more than 4.5 years. The cataract was found in 9.4%. The cut-off point for the development of cataracts was 9.5 years, with a 6.96-fold increased risk. The longer duration of hypoparathyroidism of any etiology was associated with more frequent cataract (p=0.0018).We found brain calcification in 4%, arrhythmias in 7.2% and neuropsychiatric symptoms in 5.15% of cases. Generally, the BMD in the studied group corresponded to age values, and there was no evidence for the phenomenon of high bone density. TBS was consistent with normal bone microarchitectonics. In our study, the majority of patients (83.5%) was treated with standard therapy of calcium and vitamin D supplements. 5 patients with severe disease course were treated with rhPTH (1-34).

CONCLUSIONS

Analysis of the presented database indicates insufficient diagnosis of the complications associated with chronic hypoparathyroidism. Overall, hypoparathyroidism is associated with higher risks of renal stone formation, decreased GFR, cataract especially in patients with longer duration of disease.

Bone quality in hypoparathyroidism

Hypoparathyroidism is a rare disorder characterized by hypocalcemia and deficient or absent levels of parathyroid hormone. The consequences of chronic hypoparathyroidism involve classic target organs of parathyroid hormone, namely the skeleton and the kidneys. In this article, we focus on the abnormalities in bone quality that are associated with hypoparathyroidism. As assessed by several modalities, bone quality is compromised. The evidence for abnormal bone quality includes findings from bone histomorphometry, bone material properties, and high-resolution peripheral computed tomography. These abnormalities include low bone turnover, altered skeletal microarchitecture and bone material properties. How these abnormalities relate to fracture risk are under investigation. In this study, we also reviewed the therapeutic effects of parathyroid hormone as replacement therapy in this disease.

Bone microstructure of adult patients with non-surgical hypoparathyroidism assessed by high-resolution peripheral quantitative computed tomography

There is limited evidence regarding changes in bone microstructure in patients with hypoparathyroidism. In the current study, we used a non-invasive technique to assess bone structure in hypoparathyroidism patients and discovered site-specific changes which were mainly influenced by age and menstrual status. Such changes were more prominent in the trabeculae as well as in non-surgical as opposed to post-surgical patients.

INTRODUCTION

Hypoparathyroidism (hypoPT) is a rare disease characterized by the lack of parathyroid hormone. There is limited evidence regarding changes in bone microstructure in patients with non-surgical hypoPT. We investigated bone microstructure of patients with non-surgical hypoPT using a non-invasive technique.

METHODS

Patients with hypoPT were assessed using high-resolution peripheral quantitative computed tomography (HR-pQCT) and compared to age- and sex-matched healthy controls randomly selected from a pre-existing HR-pQCT database in a cross-sectional study. Preliminary comparison between patients with different etiologies of hypoPT was performed. Associations between bone microstructure and clinical parameters were investigated using correlation and regression analyses.

RESULTS

A total of 94 patients with non-surgical hypoPT were recruited. Patients displayed an increase in trabecular volumetric BMD of the tibia (170.57 ± 34.32 vs. 156.48 ± 40.55 mg HA/cm³, p = 0.011) and increase in trabecular number of both the radius (1.48 ± 0.29 vs. 1.36 ± 0.22 mm^-1, p = 0.003) and tibia (1.42 ± 0.23 vs. 1.24 ± 0.22 mm^-1, p < 0.001) compared to healthy controls. Trabecular number was higher for non-surgical hypoPT compared to post-surgical hypoPT (1.37 ± 0.25 and 1.17 ± 0.13 mm^-1, p = 0.022). Trends towards increase in cortical volumetric BMD were only present for post-menopausal female and male patients above the age of 50. For female patients, cortical volumetric BMD and area increased with age and decreased after menopause. For males, age had little influence on bone microstructure, but cortical porosity increased with longer treatment durations.

CONCLUSIONS

Results from this pilot study suggested that both cortical and trabecular bone were altered in this group of patients with hypoPT. Etiology for hypoPT might influence bone microstructure, mainly on trabeculae. Age, menstrual status, and treatment duration were likely to influence bone microstructure in hypoPT.

Physical Activity-Dependent Regulation of Parathyroid Hormone and Calcium-Phosphorous Metabolism

Exercise perturbs homeostasis, alters the levels of circulating mediators and hormones, and increases the demand by skeletal muscles and other vital organs for energy substrates. Exercise also affects bone and mineral metabolism, particularly calcium and phosphate, both of which are essential for muscle contraction, neuromuscular signaling, biosynthesis of adenosine triphosphate (ATP), and other energy substrates. Parathyroid hormone (PTH) is involved in the regulation of calcium and phosphate homeostasis. Understanding the effects of exercise on PTH secretion is fundamental for appreciating how the body adapts to exercise. Altered PTH metabolism underlies hyperparathyroidism and hypoparathyroidism, the complications of which affect the organs involved in calcium and phosphorous metabolism (bone and kidney) and other body systems as well. Exercise affects PTH expression and secretion by altering the circulating levels of calcium and phosphate. In turn, PTH responds directly to exercise and exercise-induced myokines. Here, we review the main concepts of the regulation of PTH expression and secretion under physiological conditions, in acute and chronic exercise, and in relation to PTH-related disorders.

Recent advances in understanding and managing hypoparathyroidism

Hypoparathyroidism is a rare endocrine disorder which leads to hypocalcemia, hypercalciuria, and hyperphosphatemia. Complications include nephrocalcinosis with renal dysfunction, reduced quality of life, and abnormal skeletal properties. Conventional therapy with calcium and vitamin D analogs addresses hypocalcemia but has important limitations. Parathyroid hormone (PTH) therapy is a fundamental advance, although the effects of PTH on long-term complications require additional testing. Continuous PTH therapy is likely to be particularly advantageous for addressing renal, quality of life, and skeletal complications. Overall, much progress has been made, yet more information is needed to improve our understanding and management of hypoparathyroidism.

A registry for patients with chronic hypoparathyroidism in Russian adults

Hypoparathyroidism and pseudohypoparathyroidism are rare endocrine disorders, characterized by low serum calcium due to inappropriate parathyroid hormone (PTH) levels or resistance to its action. There is little epidemiological information regarding chronic hypoparathyroidism in Russia. This study aims to build a registry database of Russian patients with chronic hypoparathyroidism who were referred for hospital treatment in order to conduct initial analysis of clinical presentations and hospital management. The Italian registry model was taken to be able to integrate our data in the future. Two hundred patients with hypoparathyroidism (n = 194) and pseudohypoparathyroidism (n = 6) were enrolled over 2 years (2017-2019). The most frequent cause of hypoparathyroidism was neck surgery (82.5%, mostly females), followed by idiopathic hypoparathyroidism (10%), syndromic forms of genetic hypoparathyroidism (4.5%) and forms of defective PTH action (3%). Calcium supplements and alfacalcidol were prescribed in most cases. However, a minority of patients (n = 6) needed to receive teriparatide as the only way to maintain calcium levels and to prevent symptoms of hypocalcemia. Consequently, substitution treatment with parathyroid hormone should be available in certain cases of hypoparathyroidism. This database will be useful to estimate the potential requirement for recombinant PTH in Russia and standards for clinical and therapeutic approaches.

Hypoparathyroidism

BACKGROUND

Hypoparathyroidism is a rare endocrine disorder characterized by hypocalcemia and low or undetectable levels of parathyroid hormone.

METHODS

This review is an evidence-based summary of hypoparathyroidism in terms of relevant pathophysiological, clinical, and therapeutic concepts.

RESULTS

Many clinical manifestations of hypoparathyroidism are due to the lack of the physiological actions of parathyroid hormone on its 2 major target organs: the skeleton and the kidney. The skeleton is inactive, accruing bone without remodeling it. The kidneys lose the calcium-conserving actions of parathyroid hormone and, thus, excrete a greater fraction of calcium. Biochemical manifestations, besides hypocalcemia and low or undetectable levels of parathyroid hormone, include hyperphosphatemia and low levels of 1,25-dihydroxyvitamin D. Calcifications in the kidney, brain, and other soft tissues are common. Removal of, or damage to, the parathyroid glands at the time of anterior neck surgery is, by far, the most likely etiology. Autoimmune destruction of the parathyroid glands and other genetic causes represent most of the other etiologies. Conventional treatment with calcium and active vitamin D can maintain the serum calcium level but high doses may be required, adding to the risk of long-term soft tissue calcifications. The advent of replacement therapy with recombinant human PTH(1-84) represents a major step in the therapeutics of this disease.

CONCLUSIONS

Advances in our knowledge of hypoparathyroidism have led to greater understanding of the disease itself and our approach to it.

Characterising variability and regional correlations of microstructure and mechanical competence of human tibial trabecular bone: An in-vivo HR-pQCT study

OBJECTIVE

Quantifying spatial distribution of trabecular bone mechanical competence and microstructure is important for early diagnosis of skeletal disorders and potential risk of fracture. The objective of this study was to determine a spatial distribution of trabecular mechanical and morphological properties in human distal tibia and examine the contribution of regional variability of trabecular microarchitecture to mechanical competence.

METHODS

A total of 340 representative volume elements at five anatomic regions of trabecular bone - anterior, posterior, lateral, medial and centre - from ten white European-origin postmenopausal women were studied. Region-specific trabecular parameters such as trabecular volume fraction, trabecular thickness, trabecular number, trabecular surface area, trabecular separation, plate-like structure fraction and finite element analysis of trabecular stiffness were determined based on in-vivo high resolution peripheral quantitative computed tomographic (HR-pQCT) images of distal tibiae from ten postmenopausal women. Mean values were compared using analysis of variance. The correlations between morphological parameters and stiffness were calculated.

RESULTS

Significant regional variation in trabecular microarchitecture of the human distal tibia was observed (p < 0.05), with up to 106% differences between lowest (central and anterior) and highest (medial and posterior) regions. Higher proportion of plate-like trabecular morphology (63% and 53%) was found in medial and posterior regions in the distal tibia. Stiffness estimated from finite element models also differed significantly (p < 0.05), with stiffness being 4.5 times higher in the highest (medial) than lowest (central) regions. The bone volume fraction was the strongest correlate of stiffness in all regions.

CONCLUSION

A novel finding of this study is the fact that significant regional variation of stiffness derived from two-phased FEA model with individual trabecula representation correlated highly to regional morphology obtained from in-vivo HR-pQCT images at the distal tibia. The correlations between regional morphological parameters and mechanical competence of trabecular bone were consistent at all regions studied, with regional BV/TV showing the highest correlation. The method developed for regional analysis of trabecular mechanical competence may offer a better insight into the relationship between mechanical behaviour and microstructure of bone. The findings provide evidence needed to further justify a larger-cohort feasibility study for early detection of bone degenerative diseases: examining regional variations in mechanical competence and trabecular specifications may allow better understanding of fracture risks in addition to others contributing factors.

Hypoparathyroidism: is it that easy to treat?

Hypoparathyroidism is a relatively rare endocrine disease characterised by either null or inappropriately low secretion of parathyroid hormone (PTH) for serum calcium levels. The other main laboratory findings include hypocalcaemia, inappropriately normal or high urine calcium excretion and hyperphosphataemia with low urine phosphate excretion. The management of hypoparathyroidism should be tailored to each individual case, which makes it a demanding undertaking in everyday clinical practice. In this review, we sought to focus on the diagnostic approach of hypoparathyroidism and the therapeutic challenges of the disease from a clinical perspective. Conventional treatment with vitamin D analogues and calcium salts is no longer the only available treatment, since replacement treatment with PTH(1-84) has recently been approved for the disease. However, the optimal treatment schedule is yet to be defined.

Skeletal Manifestations of Hypoparathyroidism

Chronic PTH deficiency has a marked effect on the skeleton, leading to characteristic decreases in bone remodeling and increases in bone mass. An effect on fracture risk has not been demonstrated, although biochemical, imaging, and histomorphometric data indicate abnormalities in skeletal properties^1,21,21,21,2. Replacement with PTH leads to a new skeletal state that is maintained with long-term treatment.

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.

Skeletal Manifestations of Hypoparathyroidism

Chronic parathyroid hormone (PTH) deficiency has a marked effect on the skeleton, leading to characteristic decreases in bone remodeling and increases in bone mass. Numerous lines of evidence using biochemical, imaging, and histomorphometric methodologies have demonstrated that the skeleton is altered when PTH is absent and that these abnormalities might be reversed with PTH treatment. More evidence is needed to determine whether fracture risk is altered in hypoparathyroidism.

Clinical presentation and management of hypoparathyroidism

The clinical manifestations of hypoparathyroidism are variable and can involve almost any organ system. The main clinical features of the hypoparathyroidism are typically signs or symptoms due to neuromuscular irritability owing to low serum calcium level. In addition to hypocalcemia, hyperphosphatemia can contribute to long-term complications, including extra-skeletal calcifications. Bone turnover markers are generally decreased, and bone mass density is usually normal-increased compared to age- and gender-matched controls. It is still unclear whether or not these bone features could have an impact on the risk of fracture. Impaired renal function is a common complication described in patients treated for hypoparathyroidism. Other complications include premature cataracts, seizures, basal ganglia calcifications, and cardiac arrhythmias. Lastly, some clinical studies have also reported a reduced quality of life of patients with hypoparathyroidism. Increased awareness of the clinical manifestations of this disease is important to improve its clinical management.

The Effects of Long-term Administration of rhPTH(1-84) in Hypoparathyroidism by Bone Histomorphometry

Hypoparathyroidism is a rare disorder that is associated with abnormal bone properties. Recombinant human parathyroid hormone (1-84) [rhPTH(1-84)] in short-term studies has beneficial skeletal effects. Although rhPTH(1-84) will likely be used indefinitely, long-term effects on skeletal microstructure are unknown. We therefore studied histomorphometric changes with transiliac crest bone biopsies before and after 8.3 ± 1 years of rhPTH(1-84) in 13 hypoparathyroid subjects compared with 45 controls. Before institution of rhPTH(1-84), skeletal remodeling indices were markedly suppressed. With long-term treatment, indices of bone remodeling increased. Mineralizing surface increased by 26-fold (0.3 ± 1 to 7.9 ± 7%, p = 0.003), bone formation rate increased by 15-fold (0.003 ± 0.01 to 0.047 ± 0.05 μm² /μm/day, p = 0.007), osteoid width doubled (1.9 ± 1 to 4.3 ± 1 lamellae, p = 0.017), and osteoid surface tripled (3.3 ± 3 to 10.8 ± 6%, p = 0.011). Bone resorption as measured by eroded surface increased (4.6 ± 2 to 7.5 ± 3%, p = 0.021). Structural changes demonstrated intratrabecular tunneling, with increases in cancellous bone volume (19.6 ± 5 to 29.1 ± 11%, p = 0.017) and trabecular number (1.8 ± 1 to 2.5 ± 1 #/mm, p = 0.025). Cortical porosity tended to increase (6.3 ± 5 to 9.5 ± 3%, p = 0.07). Mineralizing surface, osteoid surface, and eroded surface surpassed control levels, as did cancellous bone volume, trabecular number, and cortical porosity. These data, the first to reflect such long exposure of any PTH for any disease, illustrate that PTH establishes and maintains a new skeletal state for at least 8 years in hypoparathyroidism. © 2018 American Society for Bone and Mineral Research.

Hypocalcemic disorders

Calcium is vital for life, and extracellular calcium concentrations must constantly be maintained within a precise concentration range. Low serum calcium (hypocalcemia) occurs in conjunction with multiple disorders and can be life-threatening if severe. Symptoms of acute hypocalcemia include neuromuscular irritability, tetany, and seizures, which are rapidly resolved with intravenous administration of calcium gluconate. However, disorders that lead to chronic hypocalcemia often have more subtle manifestations. Hypoparathyroidism, characterized by impaired secretion of parathyroid hormone (PTH), a key regulatory hormone for maintaining calcium homeostasis, is a classic cause of chronic hypocalcemia. Disorders that disrupt the metabolism of vitamin D can also lead to chronic hypocalcemia, as vitamin D is responsible for increasing the gut absorption of dietary calcium. Treatment and management options for chronic hypocalcemia vary depending on the underlying disorder. For example, in patients with hypoparathyroidism, calcium and vitamin D supplementation must be carefully titrated to avoid symptoms of hypocalcemia while keeping serum calcium in the low-normal range to minimize hypercalciuria, which can lead to renal dysfunction. Management of chronic hypocalcemia requires knowledge of the factors that influence the complex regulatory axes of calcium homeostasis in a given disorder. This chapter discusses common and rare disorders of hypocalcemia, symptoms and workup, and management options including replacement of PTH in hypoparathyroidism.

Feasibility of autologous plasma gel for tonsil-derived stem cell therapeutics in hypoparathyroidism

Hypoparathyroidism is a deficiency of the parathyroid hormone (PTH) in the body. We previously reported the possibility of treating it using tonsil-derived mesenchymal stem cells (TMSCs) differentiated into PTH-releasing cells. The purpose of this study was to evaluate the feasibility of using autologous plasma gel as scaffold material in treatment of hypoparathyroidism with TMSC. We obtained plasma by venous sampling of autologous blood and centrifuged and fabricated the plasma gel using a sinusoidal pattern heating machine. After we created the hypoparathyroidism animal model, we administered undifferentiated TMSCs and TMSCs differentiated into parathyroid cells at each rat dorsum by intramuscular injection with and without the plasma gel. In the plasma gel groups, intact PTH was detected from on day 21 after TMSC injection; we did not detect intact PTH in the groups that were only transplanted with TMSCs during the entire experimental period. Serum calcium was higher and phosphorous was lower in the TMSC with plasma gel groups than in the groups with TMSCs alone. We detected PTH and chromogranin A in the TMSC-plasma gel-transplanted areas on immunohistochemistry and immunofluorescence stain. Plasma gel can be considered as a cell-delivery scaffold for treating hypoparathyroidism with tonsil-derived mesenchymal stem cells.

HypoparaNet: A Database of Chronic Hypoparathyroidism Based on Expert Medical-Surgical Centers in Italy

Hypoparathyroidism is a rare disease characterized by low serum calcium levels and absent or deficient parathyroid hormone level. Regarding the epidemiology of chronic hypoparathyroidism, there are limited data in Italy and worldwide. Therefore, the purpose of this study was to build a unique database of patients with chronic hypoparathyroidism, derived from the databases of 16 referral centers for endocrinological diseases, affiliated with the Italian Society of Endocrinology, and four centers for endocrine surgery with expertise in hypoparathyroidism, to conduct an epidemiological analysis of chronic hypoparathyroidism in Italy. The study was approved by the Institutional Review Board. A total of 537 patients with chronic hypoparathyroidism were identified. The leading etiology was represented by postsurgical hypoparathyroidism (67.6%), followed by idiopathic hypoparathyroidism (14.6%), syndromic forms of genetic hypoparathyroidism (11%), forms of defective PTH action (5.2%), non-syndromic forms of genetic hypoparathyroidism (0.9%), and, finally, other forms of acquired hypoparathyroidism, due to infiltrative diseases, copper or iron overload, or ionizing radiation exposure (0.7%). This study represents one of the first large-scale epidemiological assessments of chronic hypoparathyroidism based on data collected at medical and/or surgical centers with expertise in hypoparathyroidism in Italy. Although the study presents some limitations, it introduces the possibility of a large-scale national survey, with the final aim of defining not only the prevalence of chronic hypoparathyroidism in Italy, but also standards for clinical and therapeutic approaches.

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Parathormone (PTH), produced by parathyroid glands, is the main regulator of calcium homeostasis. Hypoparathyroidism (hypoPT), due to decrease of PTH production, is a rare disease. Symptoms are multiple, altering function of several organs and leading to a decrease of quality of life. Acquired etiologies, including thyroïdectomy, the main cause of hypoPT, can be distinguished from congenital etiologies, including genetic defects. HypoPT, which is classically treated by supplementation by calcium and active vitamin D, can now be treated by recombinant injection in certain indications as a poor control under classical therapy. Here are summarized current knowledge on etiologies, epidemiology, clinical manifestations and management of hypoPT.

Hypoparathyroidism

Hypoparathyroidism is a disease characterized by inadequately low circulating concentrations of parathyroid hormone (PTH) resulting in low calcium levels and increased phosphate levels in the blood. Symptoms of the disease result from increased neuromuscular irritability caused by hypocalcaemia and include tingling, muscle cramps and seizures. The most common cause of the disease is inadvertent removal of, or injury to, the parathyroid glands during neck surgery, followed by genetic, idiopathic and autoimmune aetiologies. Conventional treatment includes activated vitamin D and/or calcium supplements, but this treatment does not fully replace the functions of PTH and can lead to short-term problems (such as hypocalcaemia, hypercalcaemia and increased urinary calcium excretion) and long-term complications (which include nephrocalcinosis, kidney stones and brain calcifications). PTH replacement has emerged as a new treatment option. Clinical trials using human PTH(1-34) and PTH(1-84) showed that this treatment was safe and effective in studies lasting up to 6 years. Recombinant human PTH(1-84) has been approved in the United States and Europe for the management of hypoparathyroidism; however, its effect on long-term complications is still being evaluated. Clinical practice guidelines, which describe the consensus of experts in the field, have been published and recognize the need for more research to optimize care. In this Primer, we summarize current knowledge of the prevalence, pathophysiology, clinical presentation and management of hypoparathyroidism.

Bone imaging in hypoparathyroidism

Hypoparathyroidism (HypoPT) is an uncommon endocrine disorder characterized by chronic deficiency or absence of parathyroid hormone (PTH), which leads to a profound reduction in bone remodeling. Subjects with HypoPT typically have bone mineral densities (BMDs) by dual-energy X-ray absorptiometry (DXA) above average at all skeletal sites, with greatest scores observed at the lumbar spine. Trabecular bone score (TBS), an indirect measure of bone microarchitecture, also appears to be normal in HypoPT. By peripheral quantitative computed tomography (pQCT) of the radius, volumetric BMD at cancellous and cortical compartments, as well as cortical area and thickness, are greater in hypoparathyroid subjects than in controls. The use of high-resolution pQCT (HRpQCT) confirmed the increase in cortical volumetric BMD but demonstrated reduced cortical thickness, associated with lower cortical porosity in HypoPT. Trabeculae tend to be more numerous but thinner in hypoparathyroid subjects. It is not clear whether these structural and the dynamic skeletal abnormalities in HypoPT affect bone strength or fracture risk. Treatment of HypoPT with PTH leads to improvement in bone remodeling rate, variable changes in bone density, and a transient increase in estimated bone strength. The effect of PTH therapy on fracture risk remains unknown. This article reviews skeletal involvement and the effect of PTH treatment in patients with HypoPT, as assessed by DXA, TBS, QCT, and HRpQCT. Data on bone strength and fracture risk in HypoPT are also reviewed here.

Management of Hypoparathyroidism: Summary Statement and Guidelines

OBJECTIVE

Hypoparathyroidism is a rare disorder characterized by hypocalcemia and absent or deficient PTH. This report presents a summary of current information about epidemiology, presentation, diagnosis, clinical features, and management and proposes guidelines to help clinicians diagnose, evaluate, and manage this disorder.

PARTICIPANTS

Participants in the First International Conference on the Management of Hypoparathyroidism represented a worldwide constituency with acknowledged interest and expertise in key basic, translational, and clinical aspects of hypoparathyroidism. Three Workshop Panels were constituted to address questions for presentation and discussion at the Conference held in Florence, Italy, May 7-9, 2015. At that time, a series of presentations were made, followed by in-depth discussions in an open forum. Each Workshop Panel also met in closed sessions to formulate the three evidence-based reports that accompany this summary statement. An Expert Panel then considered this information, developed summaries, guidelines, and a research agenda that constitutes this summary statement.

EVIDENCE

Preceding the conference, each Workshop Panel conducted an extensive literature search as noted in the individual manuscripts accompanying this report. All presentations were based upon the best peer-reviewed information taking into account the historical and current literature.

CONSENSUS PROCESS

This report represents the Expert Panel's synthesis of the conference material placed in a context designed to be relevant to clinicians and those engaged in cutting-edge studies of hypoparathyroidism.

CONCLUSIONS

This document not only provides a summary of our current knowledge but also places recent advances in its management into a context that should enhance future advances in our understanding of hypoparathyroidism.

Effects of Parathyroid Hormone Administration on Bone Strength in Hypoparathyroidism

The microstructural skeletal phenotype of hypoparathyroidism (HypoPT), a disorder of inadequate parathyroid hormone secretion, is altered trabecular microarchitecture with increased trabecular bone volume and thickness. Using 2-D histomorphometric analysis, we previously found that 2 years of PTH(1-84) in HypoPT is associated with reduced trabecular thickness (Tb.Th) and an increase in trabecular number (Tb.N). We have now utilized direct 3-D microstructural analysis to determine the extent to which these changes may be related to bone strength. Iliac crest bone biopsies from HypoPT subjects (n = 58) were analyzed by microcomputed tomography (μCT) and by microfinite element (μFE) analysis. Biopsies were performed at baseline and at 1 or 2 years of recombinant human PTH(1-84) [rhPTH(1-84)]. In a subset of subjects (n = 13) at 3 months, we demonstrated a reduction in trabecular separation (Tb.Sp, 0.64 ± 0.1 to 0.56 ± 0.1 mm; p = 0.005) and in the variance of trabecular separation (Tb.SD, 0.19 ± 0.1 to 0.17 ± 0.1 mm; p = 0.01), along with an increase in bone volume/total volume (BV/TV, 26.76 ± 10.1 to 32.83 ± 13.5%; p = 0.02), bone surface/total volume (BS/TV, 3.85 ± 0.7 to 4.49 ± 1.0 mm(2) /mm(3) ; p = 0.005), Tb.N (1.84 ± 0.5 versus 2.36 ± 1.3 mm(-1) ; p = 0.02) and Young's modulus (649.38 ± 460.7 to 1044.81 ± 1090.5 N/mm(2) ; p = 0.049). After 1 year of rhPTH(1-84), Force increased (144.08 ± 102.4 to 241.13 ± 189.1 N; p = 0.04) and Young's modulus tended to increase (662.15 ± 478.2 to 1050.80 ± 824.1 N/m(2) ; p = 0.06). The 1-year change in cancellous mineralizing surface (MS/BS) predicted 1-year changes in μCT variables. The biopsies obtained after 2 years of rhPTH(1-84) showed no change from baseline. These data suggest that administration of rhPTH(1-84) in HypoPT is associated with transient changes in key parameters associated with bone strength. The results indicate that rhPTH(1-84) improves skeletal quality in HypoPT early in treatment. © 2016 American Society for Bone and Mineral Research.

PTH(1-84) Administration in Hypoparathyroidism Transiently Reduces Bone Matrix Mineralization

Patients with hypoparathyroidism have low circulating parathyroid (PTH) levels and higher cancellous bone volume and trabecular thickness. Treatment with PTH(1-84) was shown to increase abnormally low bone remodeling dynamics. In this work, we studied the effect of 1-year or 2-year PTH(1-84) treatment on cancellous and cortical bone mineralization density distribution (Cn.BMDD and Ct.BMDD) based on quantitative backscattered electron imaging (qBEI) in paired transiliac bone biopsy samples. The study cohort comprised 30 adult hypoparathyroid patients (14 treated for 1 year; 16 treated for 2 years). At baseline, Cn.BMDD was shifted to higher mineralization densities in both treatment groups (average degree of mineralization Cn.CaMean +3.9% and +2.7%, p < 0.001) compared to reference BMDD. After 1-year PTH(1-84), Cn.CaMean was significantly lower than that at baseline (-6.3%, p < 0.001), whereas in the 2-year PTH(1-84) group Cn.CaMean did not differ from baseline. Significant changes of Ct.BMDD were observed in the 1-year treatment group only. The change in histomorphometric bone formation (mineralizing surface) was predictive for Cn.BMDD outcomes in the 1-year PTH(1-84) group, but not in the 2-year PTH(1-84) group. Our findings suggest higher baseline bone matrix mineralization consistent with the decreased bone turnover in hypoparathyroidism. PTH(1-84) treatment caused differential effects dependent on treatment duration that were consistent with the histomorphometric bone formation outcomes. The greater increase in bone formation during the first year of treatment was associated with a decrease in bone matrix mineralization, suggesting that PTH(1-84) exposure to the hypoparathyroid skeleton has the greatest effects on BMDD early in treatment.

Review of Hypoparathyroidism

Hypoparathyroidism is a rare endocrine disorder in which parathyroid hormone (PTH) production is abnormally low or absent, resulting in low serum calcium and increased serum phosphorus. The most common cause of hypoparathyroidism is parathyroid gland injury or inadvertent removal during thyroid surgery. Current treatments include supplementation with calcium and active vitamin D, with goal albumin-corrected serum calcium level in the low-normal range of 8-9 mg/dl. Complications of the disease include renal dysfunction, nephrocalcinosis, kidney stones, extracellular calcifications of the basal ganglia, and posterior subcapsular cataracts, as well as low bone turnover and increased bone density. Until January 2015, hypoparathyroidism was the only classic endocrine disease without an available hormone replacement. Recombinant human PTH 1-84, full-length PTH, is now available for a selected group of patients with the disease who are not well controlled on the current standard therapy of calcium and active vitamin D. In addition, the role of PTH replacement on quality of life, intracerebral calcifications, cataracts, improving bone turnover, and reduction of renal complications of the disease remains to be further investigated.

Calcilytic Ameliorates Abnormalities of Mutant Calcium-Sensing Receptor (CaSR) Knock-In Mice Mimicking Autosomal Dominant Hypocalcemia (ADH)

Activating mutations of calcium-sensing receptor (CaSR) cause autosomal dominant hypocalcemia (ADH). ADH patients develop hypocalcemia, hyperphosphatemia, and hypercalciuria, similar to the clinical features of hypoparathyroidism. The current treatment of ADH is similar to the other forms of hypoparathyroidism, using active vitamin D3 or parathyroid hormone (PTH). However, these treatments aggravate hypercalciuria and renal calcification. Thus, new therapeutic strategies for ADH are needed. Calcilytics are allosteric antagonists of CaSR, and may be effective for the treatment of ADH caused by activating mutations of CaSR. In order to examine the effect of calcilytic JTT-305/MK-5442 on CaSR harboring activating mutations in the extracellular and transmembrane domains in vitro, we first transfected a mutated CaSR gene into HEK cells. JTT-305/MK-5442 suppressed the hypersensitivity to extracellular Ca(2+) of HEK cells transfected with the CaSR gene with activating mutations in the extracellular and transmembrane domains. We then selected two activating mutations locating in the extracellular (C129S) and transmembrane (A843E) domains, and generated two strains of CaSR knock-in mice to build an ADH mouse model. Both mutant mice mimicked almost all the clinical features of human ADH. JTT-305/MK-5442 treatment in vivo increased urinary cAMP excretion, improved serum and urinary calcium and phosphate levels by stimulating endogenous PTH secretion, and prevented renal calcification. In contrast, PTH(1-34) treatment normalized serum calcium and phosphate but could not reduce hypercalciuria or renal calcification. CaSR knock-in mice exhibited low bone turnover due to the deficiency of PTH, and JTT-305/MK-5442 as well as PTH(1-34) increased bone turnover and bone mineral density (BMD) in these mice. These results demonstrate that calcilytics can reverse almost all the phenotypes of ADH including hypercalciuria and renal calcification, and suggest that calcilytics can become a novel therapeutic agent for ADH.

Transient Increased Calcium and Calcitriol Requirements After Discontinuation of Human Synthetic Parathyroid Hormone 1-34 (hPTH 1-34) Replacement Therapy in Hypoparathyroidism

Synthetic human PTH 1-34 (hPTH 1-34) replacement therapy in hypoparathyroidism maintains eucalcemia and converts quiescent bone to high-turnover bone. However, the skeletal and metabolic effects of drug discontinuation have not been reported. Nine subjects with hypoparathyroidism received subcutaneous injections of hPTH 1-34 two to three times daily for 19.8 to 61.3 months and then transitioned back to calcium and calcitriol. Biochemistries and bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) were assessed at baseline, while on treatment, and at follow-up 3 to 12 months after drug discontinuation. Two subjects developed hypocalcemia when hPTH 1-34 was abruptly discontinued. Thus, to avoid hypocalcemia, subjects were slowly weaned from hPTH 1-34 over several weeks. When hPTH 1-34 was stopped, subjects were requiring two to three times pretreatment doses of calcitriol and calcium to maintain blood calcium levels. Doses were gradually reduced over many weeks until calcium levels were stable on doses similar to baseline. Bone-specific alkaline phosphatase (BSAP), N-telopeptide (NTX), and osteocalcin (OC) increased significantly with hPTH 1-34; at follow-up, BSAP and NTX had returned to baseline while OC was still slightly elevated. During treatment, BMD was unchanged at the hip and lateral spine but declined at the anterior-posterior (AP) spine, radius, and total body. During weaning, BMD increased, with the hip and lateral spine exceeding pre-hPTH 1-34 values and the whole body returning to baseline. AP spine was increased non-significantly compared to baseline at follow-up. hPTH 1-34 must be gradually weaned in hypoparathyroid patients with high doses of oral medications given to avoid hypocalcemia. The transient increased requirements accompanied by increased BMD after long-term hPTH 1-34 therapy suggest a reversal of the expanded remodeling space favoring bone formation as the skeleton returns to a low-turnover state, reminiscent of the hungry bone syndrome. Further study and close monitoring is required to ensure safe transition to conventional therapy and to elucidate the physiological mechanism of this phenomenon.

Bone volume fraction and fabric anisotropy are better determinants of trabecular bone stiffness than other morphological variables

As our population ages, more individuals suffer from osteoporosis. This disease leads to impaired trabecular architecture and increased fracture risk. It is essential to understand how morphological and mechanical properties of the cancellous bone are related. Morphology-elasticity relationships based on bone volume fraction (BV/TV) and fabric anisotropy explain up to 98% of the variation in elastic properties. Yet, other morphological variables such as individual trabeculae segmentation (ITS) and trabecular bone score (TBS) could improve the stiffness predictions. A total of 743 micro-computed tomography (μCT) reconstructions of cubic trabecular bone samples extracted from femur, radius, vertebrae, and iliac crest were analyzed. Their morphology was assessed via 25 variables and their stiffness tensor (CFE) was computed from six independent load cases using micro finite element (μFE) analyses. Variance inflation factors were calculated to evaluate collinearity between morphological variables and decide upon their inclusion in morphology-elasticity relationships. The statistically admissible morphological variables were included in a multiple linear regression model of the dependent variable CFE. The contribution of each independent variable was evaluated (ANOVA). Our results show that BV/TV is the best determinant of CFE(r(2) adj  = 0.889), especially in combination with fabric anisotropy (r(2) adj  = 0.968). Including the other independent predictors hardly affected the amount of variance explained by the model (r(2) adj  = 0.975). Across all anatomical sites, BV/TV explained 87% of the variance of the bone elastic properties. Fabric anisotropy further described 10% of the bone stiffness, but the improvement in variance explanation by adding other independent factors was marginal (<1%). These findings confirm that BV/TV and fabric anisotropy are the best determinants of trabecular bone stiffness and show, against common belief, that other morphological variables do not bring any further contribution. These overall conclusions remain to be confirmed for specific bone diseases and postelastic properties.

Bone disease in hypoparathyroidism

Hypoparathyroidism is a rare disorder that may be acquired or inherited. Postsurgical hypoparathyroidism is responsible for the majority of acquired hypoparathyroidism. Bone disease occurs in hypoparathyroidism due to markedly reduced bone remodeling due to the absence or low levels of parathyroid hormone. Chronically reduced bone turnover in patients with hypoparathyroidism typically leads to higher bone mass than in age- and sex-matched controls. Whether this increased bone density reduces fracture risk is less certain, because while increased bone mineralization may be associated with increased brittleness of bone, this does not appear to be the case in hypoparathyroidism. Treatment of hypoparathyroidism with recombinant parathyroid hormone may reduce bone mineral density but simultaneously strengthen the mechanical properties of bone.

Structure Model Index Does Not Measure Rods and Plates in Trabecular Bone

Structure model index (SMI) is widely used to measure rods and plates in trabecular bone. It exploits the change in surface curvature that occurs as a structure varies from spherical (SMI = 4), to cylindrical (SMI = 3) to planar (SMI = 0). The most important assumption underlying SMI is that the entire bone surface is convex and that the curvature differential is positive at all points on the surface. The intricate connections within the trabecular continuum suggest that a high proportion of the surface could be concave, violating the assumption of convexity and producing regions of negative differential. We implemented SMI in the BoneJ plugin and included the ability to measure the amounts of surface that increased or decreased in area after surface mesh dilation, and the ability to visualize concave and convex regions. We measured SMI and its positive (SMI(+)) and negative (SMI(-)) components, bone volume fraction (BV/TV), the fraction of the surface that is concave (CF), and mean ellipsoid factor (EF) in trabecular bone using 38 X-ray microtomography (XMT) images from a rat ovariectomy model of sex steroid rescue of bone loss, and 169 XMT images from a broad selection of 87 species' femora (mammals, birds, and a crocodile). We simulated bone resorption by eroding an image of elephant trabecule and recording SMI and BV/TV at each erosion step. Up to 70%, and rarely <20%, of the trabecular surface is concave (CF 0.155-0.700). SMI is unavoidably influenced by aberrations induced by SMI(-), which is strongly correlated with BV/TV and CF. The plate-to-rod transition in bone loss is an erroneous observation resulting from the close and artifactual relationship between SMI and BV/TV. SMI cannot discern between the distinctive trabecular geometries typical of mammalian and avian bone, whereas EF clearly detects birds' more plate-like trabecule. EF is free from confounding relationships with BV/TV and CF. SMI results reported in the literature should be treated with suspicion. We propose that EF should be used instead of SMI for measurements of rods and plates in trabecular bone.

PTH(1-84) replacement therapy for the treatment of hypoparathyroidism

Hypoparathyroidism is a rare disease characterized by hypocalcemia and insufficient circulating levels of parathyroid hormone (PTH). Conventional therapy includes calcium and active vitamin D supplementation, often in large doses. Therapy with calcium and vitamin D, however, does not address certain problematic aspects of the disease, including abnormal bone metabolism and reduced quality of life. Hypoparathyroidism is the only classic endocrine deficiency disease for which the missing hormone, PTH, is not yet an approved treatment. PTH(1-84) may soon become a therapeutic option for patients with hypoparathyroidism. PTH (1-84) has been demonstrated to maintain serum calcium while reducing or eliminating requirements for calcium and active vitamin D supplementation. Data from bone densitometry, bone turnover markers and histomorphometry of bone biopsy specimens show positive structural and dynamic effects on the skeleton. PTH replacement therapy may also be associated with improved quality of life. PTH(1-84) replacement therapy for hypoparathyroidism is promising, although further acquisition of long-term data is needed.

An Analytical Approach to Investigate the Evolution of Bone Volume Fraction in Bone Remodeling Simulation at the Tissue and Cell Level

Simulation of bone remodeling at the bone cell level can predict changes in bone microarchitecture and density due to bone diseases and drug treatment. Their clinical application, however, is limited since bone microarchitecture can only be measured in the peripheral skeleton of patients and since the simulations are very time consuming. To overcome these issues, we have developed an analytical model to predict bone density adaptation at the organ level, in agreement with our earlier developed bone remodeling theory at the cellular level. Assuming a generalized geometrical model at the microlevel, the original theory was reformulated into an analytical equation that describes the evolution of bone density as a function of parameters that describe cell activity, mechanotransduction and mechanical loading. It was found that this analytical model can predict changes in bone density due to changes in these cell-level parameters that are in good agreement with those predicted by the earlier numerical model that implemented a detailed micro-finite element (FE) model to represent the bone architecture and loading, at only a fraction of the computational costs. The good agreement between analytical and numerical density evolutions indicates that the analytical model presented in this study can predict well bone functional adaptation and, eventually, provide an efficient tool for simulating patient-specific bone remodeling and for better prognosis of bone fracture risk.

Use of parathyroid hormone in hypoparathyroidism

Hypoparathyroidism is a disorder characterized by hypocalcemia, deficient PTH, and abnormal bone remodeling. Standard treatment of hypoparathyroidism consists of oral calcium and vitamin D supplementation. However, maintaining serum calcium levels can be a challenge. In addition, concerns exist regarding hypercalciuria and ectopic calcifications that can be associated with such treatment. Hypoparathyroidism is the only classic endocrine deficiency disease for which the missing hormone, PTH, is not yet an approved treatment. This review focuses on the use of PTH in the treatment of hypoparathyroidism, in the form of teriparatide [PTH(1-34)] and the full-length molecule, PTH(1-84). Studies in hypoparathyroid subjects demonstrate that PTH(1-34) and PTH(1-84) lower or abolish supplemental calcium and vitamin D requirements as well as increase markers of bone turnover. Densitometric and histomorphometric studies in some subjects treated with PTH(1- 34) and PTH(1-84) show an improvement in bone-remodeling dynamics and return of bone metabolism toward normal levels. Given the chronic nature of hypoparathyroidism, and the expectation that PTH will be used for extended periods of time in hypoparathyroidism, further studies are needed to determine the long-term safety of PTH therapy in this population.

Trabecular and cortical microarchitecture in postmenopausal HIV-infected women

Our objective was to assess the effects of HIV infection and antiretroviral therapy on trabecular and cortical microarchitecture in postmenopausal minority women. A subgroup of 106 (46 HIV-infected, 60 uninfected) postmenopausal Hispanic and African American women from an established cohort had areal bone mineral density (aBMD) measured by dual-energy X-ray absorptiometry and trabecular and cortical volumetric BMD (vBMD) and microarchitecture measured by high-resolution peripheral quantitative computed tomography (HRpQCT) at the radius and tibia. HIV-infected women were slightly younger (58 ± 1 vs. 61 ± 1 years, p = 0.08), and had lower body mass index (BMI; 28 ± 1 vs. 32 ± 1 kg/m(2), p < 0.01). BMI-adjusted aBMD Z scores were lower in HIV-infected women at the lumbar spine, total hip, and ultradistal radius. Serum N-telopeptide and C-telopeptide levels were also higher in HIV-infected women. Trabecular and cortical vBMD were similar at the radius, but cortical area (105.5 ± 2.4 vs. 120.6 ± 2.0 mm(2), p < 0.01) and thickness (956 ± 33 vs. 1,075 ± 28 μm, p < 0.01) at the tibia were approximately 11-12 % lower in HIV-infected women. Differences remained significant after adjusting for age, BMI, and race/ethnicity. In contrast, cortical porosity was similar in the two groups. Although HIV-infected postmenopausal women had lower aBMD at the spine, total hip, and ultradistal radius and higher levels of bone resorption markers, the only differences detected by HRpQCT were lower cortical thickness and area at the tibia.

PTH replacement therapy of hypoparathyroidism

Hypoparathyroidism is characterized by hypocalcemia with inappropriately low parathyroid hormone (PTH) levels. Bone turnover is abnormally low and bone mineral density (BMD) is typically increased. Plasma calcium levels can be normalized by treatment with calcium supplements and vitamin D analogs, but bone turnover remains low and patients complain of a reduced quality of life (QoL). During recent years, a number of studies have shown that PTH replacement therapy (PTH-RT) may maintain calcium levels within the normal range, while the need for calcium and vitamin D supplements is reduced. In the initial response to subcutaneous PTH injections once or twice daily, bone turnover is overstimulated. BMD increases in cancellous bone, but decreases in cortical bone due to an increased porosity. Microcomputed tomography scans and histomorphometric studies on bone biopsies have shown changes similar to the well-known bone anabolic effects of PTH treatment in osteoporosis rather than a normalization of bone remodeling balancing the anabolic and catabolic effects of PTH. Most recently, continuous PTH delivery by pump was shown to increase the levels of bone markers into the normal range (without overstimulation of bone turnover) and with a normalization of renal calcium excretion. As PTH has a short plasma half-life, these findings indicate that exposure to PTH once or twice daily is not sufficient to reestablish a calcium homeostasis and bone metabolism that resembles normal physiology. Further studies should assess the effects of continuous PTH exposure by pump delivery (or multiple daily injections) on BMD and bone histology, as well as the effects of PTH-RT on indices of QoL.

Structure and strength of the distal radius in female patients with rheumatoid arthritis: a case-control study

The purpose of this work was to investigate the volumetric bone mineral density (vBMD), bone microstructure, and mechanical indices of the distal radius in female patients with rheumatoid arthritis (RA). We report a cross-sectional study of 66 middle-aged female RA patients and 66 age-matched healthy females. Areal BMD (aBMD) of the hip, lumbar spine, and distal radius was measured by dual-energy X-ray absorptiometry (DXA). High-resolution peripheral quantitative computed tomography (HR-pQCT) was performed at the distal radius, yielding vBMD, bone microstructure, and mechanical indices. Cortical and trabecular vBMD were 3.5% and 10.7% lower, respectively, in RA patients than controls, despite comparable aBMD. Trabecular microstructural indices were -5.7% to -23.1% inferior, respectively, in RA patients compared to controls, with significant differences in trabecular bone volume fraction, separation, inhomogeneity, and structural model index. Cortical porosity volume and percentage were 128% and 93% higher, respectively, in RA patients, with stress being distributed more unevenly. Fourteen RA patients had exaggerated periosteal bone apposition primarily affecting the ulnovolar aspect of the distal radius. These particular patients were more likely to have chronic and severe disease and coexisting wrist deformity. The majority of the differences in density and microstructure between RA patients and controls did not depend on menstrual status. Recent exposure to glucocorticoids did not significantly affect bone density and microstructure. HR-pQCT provides new insight into inflammation-associated bone fragility in RA. It detects differences in vBMD, bone microstructure, and mechanical indices that are not captured by DXA. At the distal radius, deterioration in density and microstructure in RA patients involved both cortical and trabecular compartments. Excessive bone resorption appears to affect cortical more than trabecular bone at distal radius, particularly manifested as increased cortical porosity. Ulnovolar periosteal apposition of the distal radius is a feature of chronic, severe RA with wrist deformity.

Increased vertebral morphometric fracture in patients with postsurgical hypoparathyroidism despite normal bone mineral density

BACKGROUND

The mechanism behind parathyroid hormone (PTH) activation of bone remodeling is intimately dependent on the time of exposure of bone cells to hormone levels. Sustained high PTH levels trigger catabolism, while transitory elevations induce anabolism. The effects of hypoparathyroidism (PhPT) on bone are unknown. The objective was to study the impact of PhPT on bone mineral density (BMD), on the frequency of subclinical vertebral fracture and on mandible morphometry.

METHODS

The study comprised thirty-three postmenopausal women, 17 controls (CG) and 16 with PhPT (PhPTG) matched for age, weight and height. Bone mineral density (BMD) of lumbar spine, total hip and 1/3 radius, radiographic evaluation of vertebral morphometry, panoramic radiography of the mandible, and biochemical evaluation of mineral metabolism and bone remodeling were evaluated in both groups.

RESULTS

There were no significant differences in lumbar spine or total hip BMD between groups. There was marked heterogeneity of lumbar spine BMD in PhPTG (high = 4, normal = 9, osteopenia = 1, and osteoporosis = 2 patients). BMD was decreased in the 1/3 radius in PhPTG P < 0.005). The PhPTG group exhibited an increased frequency of morphometric vertebral fractures and decreased mandible cortical thickness.

CONCLUSION

The study suggests that vertebral fragility occurs in PhPT despite normal or even high BMD. The current results encourage further studies to evaluate the use of panoramic radiography in the identification of osteometabolic disorders, such as PhPT and the development of a more physiological treatment for PhPT.

Patient-specific bone modelling and remodelling simulation of hypoparathyroidism based on human iliac crest biopsies

We previously developed a load-adaptive bone modelling and remodelling simulation model that can predict changes in the bone micro-architecture as a result of changes in mechanical loading or cell activity. In combination with a novel algorithm to estimate loading conditions, this offers the possibility for patient-specific predictions of bone modelling and remodelling. Based on such models, the underlying mechanisms of bone diseases and/or the effects of certain drugs and their influence on the bone micro-architecture can be investigated. In the present study we test the ability of this approach to predict changes in bone micro-architecture during hypoparathyroidism (HypoPT), as an illustrative example. We hypothesize that, apart from reducing bone turnover, HypoPT must also lead to increased osteocyte mechanosensitivity in order to explain the changes in bone mass seen in patients. Healthy human iliac crest biopsies were used as the starting point for the simulations that mimic HypoPT conditions and the resultant micro-architectures were compared to age-matched clinical HypoPT biopsies. Simulation results were in good agreement with the clinical data when osteocyte mechanosensitivity was increased by 40%. In conclusion, the results confirm our hypothesis, and also demonstrate that patient-specific bone modelling and remodelling simulations are feasible.

Hypoparathyroidism

Hypoparathyroidism is characterized by hypocalcemia, hyperphosphatemia and low or inappropriately normal levels of parathyroid hormone (PTH). Pseudohypoparathyroidism is characterized by similar findings however PTH is elevated due to PTH resistance. PTH is a key calcium regulating hormone essential for calcium homeostasis, vitamin D-dependant calcium absorption, renal calcium reabsorption and renal phosphate clearance. The most common cause of hypoparathyroidism is iatrogenic in the setting of anterior neck surgery. Hypoparathyroidism may be due to congenital or acquired disorders. Causes include autoimmune diseases, genetic abnormalities, destruction or infiltrative disorders of the parathyroids. Impaired secretion of PTH may be seen with hypomagnesemia or hypermagnesemia Work-up includes a comprehensive history, physical examination, and a relevant biochemical investigation. Treatment of symptomatic or profound asymptomatic hypocalcemia (Corrected Calcium (Ca) < 1.9 mmol/L) is aimed at rapid intravenous administration of calcium and oral supplementation of vitamin D metabolites. Oral calcium and vitamin D analogs are critical in the treatment of hypocalcemia. In the long-term management of hypoparathyroidism thiazide diuretics are of value as they enhance renal calcium reabsorption and increase serum calcium and are of particular benefit in those with activating mutations of the calcium-sensing receptor. Parathyroid hormone replacement is of great value in improving serum calcium and lowering serum phosphate as well as the doses of calcium and calcitriol supplementation required. It has been shown to lower urinary calcium losses. Careful monitoring of vitamin D, phosphorous, and calcium is necessary during acute and long-term therapy. Although hypocalcemic patients commonly present with symptoms of neuromuscular irritability with perioral numbers paresthesias, tingling, seizures and, bronchospasm; hypocalcemia may be identified on the biochemical profile of an asymptomatic patient.

Mini-review: new therapeutic options in hypoparathyroidism

Hypoparathyroidism is a disorder characterized by hypocalcemia and low or absent parathyroid hormone (PTH). While standard treatment of hypoparathyroidism consists of oral calcium and vitamin D supplementation, maintaining serum calcium levels can be a challenge, and concerns exist regarding hypercalciuria and ectopic calcifications that can be associated with such treatment. Hypoparathyroidism is the only classic endocrine deficiency disease for which the missing hormone, PTH, is not yet an approved treatment. This mini-review focuses on the use of PTH in the treatment of hypoparathyroidism. There are two available formulations of PTH: teriparatide [human PTH(1-34)] and the full-length molecule, PTH(1-84). Both PTH(1-34) and PTH(1-84) lower supplemental vitamin D requirements and increase markers of bone turnover. Densitometric and histomorphometric studies in some subjects treated with PTH(1-84) demonstrate improvement in abnormal bone-remodeling dynamics and return of bone metabolism toward normal euparathyroid levels. Further detailed examination of skeletal features following therapy with the different treatment regimens and data regarding the effect of PTH on quality of life measures are under active investigation.

Investigation of the influence of reflection on the attenuation of cancellous bone

The model proposed in this paper is based on the fact that the reflection might have a significant contribution to the attenuation of the acoustic waves propagating through the cancellous bone. The numerical implementation of the mentioned effect is realized by the development of a new representative volume element that includes an infinitesimally thin 'transient' layer on the contact surface of the bone and the marrow. This layer serves to model the amplitude transformation of the incident wave by the transition through media with different acoustic impedances and to take into account the energy loss due to the reflection. The proposed representative volume element together with the multiscale finite element is used to simulate the wave propagation and to evaluate the attenuation coefficient for samples with different effective densities in the dependence of the applied excitation frequency. The obtained numerical values show a very good agreement with the experimental results. Moreover, the model enables the determination of the upper and the lower bound for the attenuation coefficient.

PTH(1-84) administration reverses abnormal bone-remodeling dynamics and structure in hypoparathyroidism

Hypoparathyroidism is associated with abnormal structural and dynamic skeletal properties. We hypothesized that parathyroid hormone(1-84) [PTH(1-84)] treatment would restore skeletal properties toward normal in hypoparathyroidism. Sixty-four subjects with hypoparathyroidism were treated with PTH(1-84) for 2 years. All subjects underwent histomorphometric assessment with percutaneous iliac crest bone biopsies. Biopsies were performed at baseline and at 1 or 2 years. Another group of subjects had a single biopsy at 3 months, having received tetracycline before beginning PTH(1-84) and prior to the biopsy (quadruple-label protocol). Measurement of biochemical bone turnover markers was performed. Structural changes after PTH(1-84) included reduced trabecular width (144 ± 34 µm to 128 ± 34 µm, p = 0.03) and increases in trabecular number (1.74 ± 0.34/mm to 2.07 ± 0.50/mm, p = 0.02) at 2 years. Cortical porosity increased at 2 years (7.4% ± 3.2% to 9.2% ± 2.4%, p = 0.03). Histomorphometrically measured dynamic parameters, including mineralizing surface, increased significantly at 3 months, peaking at 1 year (0.7% ± 0.6% to 7.1% ± 6.0%, p = 0.001) and persisting at 2 years. Biochemical measurements of bone turnover increased significantly, peaking at 5 to 9 months of therapy and persisting for 24 months. It is concluded that PTH(1-84) treatment of hypoparathyroidism is associated with increases in histomorphometric and biochemical indices of skeletal dynamics. Structural changes are consistent with an increased remodeling rate in both trabecular and cortical compartments with tunneling resorption in the former. These changes suggest that PTH(1-84) improves abnormal skeletal properties in hypoparathyroidism and restores bone metabolism toward normal euparathyroid levels.