Significance of primary hyperparathyroidism in the management of osteoporosis

Secondary Hyperparathyroidism

Secondary hyperparathyroidism (SHPT) does not initiate as a primary dysfunction of parathyroid glands resulting from an intrinsic defect or disease but is the physiologic response of parathyroids to metabolic changes elsewhere in the body occurring over time. SHPT is a manifestation of a chronic condition that classically occurs from chronic kidney disease. In fact, given the relatively recent transition of populations from outside (agrarian) to indoor (industrial, information technology, and so forth) employment and a consequent reduction in sun exposure, combined with diets of highly processed food, vitamin D and calcium deficiencies are now the leading causes of SHPT.

A Significant Association between Parathyroid Adenoma Volume and Bone Mineral Loss at Distal Forearm

INTRODUCTION

The cortical bone is the most severely affected site in patients with primary hyperparathyroidism (PHPT) and thus, a low bone mineral density (BMD) is predominantly observed in distal forearm. Several studies have investigated potential associations between the weight of the gland and bone mineral loss. In this study, we wanted to investigate the relationship between parathyroid adenoma (PTA) volume and bone mineral loss.

METHODS

All patients with a diagnosis of PHPT who were operated at our hospital, and with a histologically proven single PTA were retrospectively analyzed. Z-scores were used as the main variable in our analysis to eliminate the effects of age, sex and gonadal status on BMD.

RESULTS

Total of 153 patients who met the inclusion criteria were eligible for the study. A significant negative correlation between the PTA volume and z-score for distal third of the radius (DR) (p = 0.006, r = -0.297) was shown. The cut-off value of gland volume for predicting cortical bone mineral loss was 9043.2 mm3. There was also a significant negative correlation between the 24-hour urine calcium and z-scores for lumbar vertebrae and total hip. A significant negative correlation was found between preoperative 25-hydroxy vitamin D levels and the PTA weight.

CONCLUSIONS

As the first study that evaluated any possible association between the volume of a parathyroid adenoma and bone mineral loss in patients with PHPT, we found a significant negative correlation between DR z-scores and resected gland volume. Since the volume of a PTA can also be determined by a preoperative US, our findings may be helpful during the preoperative evaluation of a patient with a preliminary diagnosis of PHPT.

Impact of reference point selection on DXA-based measurement of forearm bone mineral density

Few studies have systematically evaluated the technical aspects of forearm bone mineral density (BMD) measurement. We found that BMD remained stable regardless of the reference point; however, the ROI identified was not always consistent. Our study highlights the importance of using the same reference point for serial measurements of forearm BMD.

BACKGROUND

Forearm fractures are clinically important outcomes from the perspective of morbidity, health care costs, and interruption of work. BMD of the forearm, as derived by dual-energy x-ray absorptiometry (DXA), is a better predictor of fracture at the forearm compared with BMD measured at other sites. However, very few studies have evaluated the technical aspects of selecting the ROI for forearm BMD measurement. This study aimed to compare the BMD values measured at the 1/3 radius site using three different reference points: the ulnar styloid process, the radial endplate, and the bifurcation of the ulna and radius.

METHODOLOGY

Healthy Chinese patients participating in the control group of an ongoing study at Zhejiang Provincial People's Hospital were recruited for this study. For each patient, a DXA scan (GE Lunar Prodigy) of the forearm was performed and BMD values were separately calculated using each of the three reference points to identify the ROI. Pearson correlation coefficients were calculated to examine the correlation between the BMD measures derived from each reference point. The F test and independent t test were applied for more robust analysis of the differences in the variances and means.

RESULTS

Sixty-eight healthy Chinese volunteers agreed to participate in this study. The root mean square standard deviation (RMS-SD) percentages of BMD values measured at the 1/3 radius site were 2.19%, 2.23%, and 2.20% when using the ulnar styloid process, radial endplate, and the bifurcation of the ulna and radius as the reference points, respectively. Pearson's correlation coefficients for all pairwise comparisons among these three groups were greater than 0.99. F tests and independent t tests showed p values ranging from 0.92 to 0.99. However, we observed that among 10% of patients, choosing an ROI at the ulnar styloid process led to an inability to accurately determine the BMD at the ultra-distal radius.

CONCLUSIONS

Given equal ability to determine BMD at the 1/3 radius accurately, the radial endplate or the bifurcation of the ulna and radius should be preferentially selected as the reference point for routine forearm BMD measurements in order to avoid situations in which the ultra-distal radius BMD cannot be determined.

Lifelong challenge of calcium homeostasis in male mice lacking TRPV5 leads to changes in bone and calcium metabolism

Trpv5 plays an important role in calcium (Ca²⁺) homeostasis, among others by mediating renal calcium reabsorption. Accordingly, Trpv5 deficiency strongly stresses Ca²⁺ homeostasis in order to maintain stable serum Ca²⁺. We addressed the impact of lifelong challenge of calcium homeostasis on the bone phenotype of these mice.

Aging significantly increased serum 1,25(OH)₂D₃ and PTH levels in both genotypes but they were more elevated in Trpv5^−/− mice, whereas serum Ca²⁺ was not affected by age or genotype. Age-related changes in trabecular and cortical bone mass were accelerated in Trpv5^−/− mice, including reduced trabecular and cortical bone thickness as well as reduced bone mineralization. No effect of Trpv5 deficiency on bone strength was observed. In 78-week-old mice no differences were observed between the genotypes regarding urinary deoxypyridinoline, osteoclast number, differentiation and activity as well as osteoclast precursor numbers, as assessed by flow cytometry.

In conclusion, life-long challenge of Ca²⁺ homeostasis present in Trpv5^−/− mice causes accelerated bone aging and a low cortical and trabecular bone mass phenotype. The phenotype of the Trpv5^−/− mice suggests that maintenance of adequate circulatory Ca²⁺ levels in patients with disturbances in Ca²⁺ homeostasis should be a priority in order to prevent bone loss at older age.

Mild primary hyperparathyroidism as defined in the Italian Society of Endocrinology's Consensus Statement: prevalence and clinical features

BACKGROUND

Mild primary hyperparathyroidism (PHPT) was recently clearly defined for the first time. Our study was thus aimed to pinpoint proportion and clinical characteristics of this kind of patients.

DESIGN AND PATIENTS

We retrospectively evaluated our series of 360 consecutive patients with PHPT, selecting those with all features allowing a correct classification (serum total and ionized calcium, phosphate, creatinine, PTH, 25OHD, urinary calcium, renal and neck ultrasound, MIBI scintiscan, and DEXA at lumbar spine, femoral neck, and distal third of radius). Patients were defined asymptomatic (aPHPT) when bone or kidney was not involved and no hypercalcemic symptom occurred; mild PHPT was defined as aPHPT not meeting updated surgical criteria.

RESULTS

Seventy-five patients among 172 classified as aPHPT had all available data required for surgical evaluation and could be evaluated. Sixty/75 met surgical criteria and the remaining 15 were classified as mild. Mild PHPT patients had lower total and ionized calcium, urinary calcium, and PTH levels than aPHPT meeting surgical criteria, while vitamin D levels and BMD were similar.

CONCLUSIONS

Mild PHPT strictly defined according to the last consensus represents a small subgroup with a less active form of the disease.

What is the utility of distal forearm DXA in primary hyperparathyroidism?

BACKGROUND

Primary hyperparathyroidism (PHPT) leads to increased bone turnover, low bone mineral density, and increased fracture risk. These effects are, however, preferentially seen in the distal forearm, which is rich in cortical bone. This study aimed to determine how frequently the distal forearm T score was the worst T score and if this T score alone led to higher rate of diagnosis of osteopenia or osteoporosis.

MATERIALS AND METHODS

We retrospectively reviewed a prospective database of 300 patients undergoing parathyroidectomy at our institution between November 2000 and January 2009. The bone mineral density of the lumbar spine, total proximal femurs, and distal third of the nondominant radius was measured by dual x-ray absorptiometry. Data on bone density are reported as T scores.

RESULTS

The mean T scores were -1.30 ± 0.2 in the distal forearm, -1.0 ± 0.1 in the total proximal femurs, and -0.9 ± 0.1 in the spine. The distal forearm T score was the worst bone mineral density T score in 39% of patients. This T score alone led to an upstaging in diagnosis to osteopenia or osteoporosis in 9.4% of patients.

CONCLUSION

In patients with PHPT, the worst T score is commonly found in the distal forearm. This T score can identify additional patients with a diagnosis of osteopenia or osteoporosis. Distal forearm bone mineral density should, therefore, be assessed in all patients who have a diagnosis of PHPT.

Lifetime high calcium intake increases osteoporotic fracture risk in old age

Caloric restriction prolongs life span. Calcium restriction may preserve bone health. In osteoporosis, bone mineral density (BMD) has significantly decreased, due to a lack of osteoblast bone formation. Traditional osteoporosis prevention is aimed at maximizing BMD, but the lifetime effects of continuously maintaining a high BMD on eventual bone health in old age, have not been studied. Strikingly, in countries with a high mean BMD, fracture rates in the elderly are significantly higher than in countries with a low mean BMD. Studies show that this is not based on genetic differences. Also, in primary hyperparathyroidism, on the brink of osteoporosis, BMD levels may be significantly higher than normal. Maybe, BMD does not represent long term bone health, but merely momentary bone strength. And maybe, maintaining a high BMD might actually wear out bone health. Since osteoporosis particularly occurs in the elderly, and because in osteoporotic bone less osteoblasts are available, the underlying process may have to do with ageing of osteoblastic cells. In healthy subjects, osteoblastic bone cells respond to the influx of calcium by composing a matrix upon which calcium precipitates. In the process of creating this matrix, 50-70% of the involved osteoblasts die. The greater the influx of calcium, the greater osteoblast activity, and the greater osteoblast apoptosis rate. An increased osteoblast apoptosis rate leads to a decrease in the age-related osteoblast replicative capacity (ARORC). In comparison to healthy bone, in osteoporotic bone the decrease in the replicative capacity of osteoblastic cells is greater. Due to the eventual resulting lack of osteoblast activity, micro-fractures cannot be repaired. Continuously maintaining a high BMD comes with continuously high bone remodeling rates, which regionally exhaust the ARORC, eventually leading to irreparable microfractures. Regarding long time influences on bone health, adequate estrogen levels are known to be protective against osteoporosis. This is generally attributed to its inhibiting influence on osteoclast activity. Instead, its net effects on osteoblast metabolism may be the key to osteoporosis prevention. Adequate estrogen levels inhibit osteoblast activity, calcium apposition and osteoblast apoptosis rate, preserving the ARORC.

CONCLUSION

Regarding osteoporosis prevention, ARORC better than BMD represents bone health. Regarding ARORC, adequate estrogen levels are protective, opposing the similar effects of hyperparathyroidism and a high calcium diet. Tests need to be performed in mice to assess the lifetime effects of a high versus a low calcium diet, on eventual bone fracture toughness.