Regulation of calcium-parathyroid hormone feedback in primary hyperparathyroidism: effects of bisphosphonate treatment

Contemporary Medical Management of Primary Hyperparathyroidism: A Systematic Review

INTRODUCTION

Primary hyperparathyroidism is increasingly an asymptomatic disease at diagnosis, but the recognized guidelines for management are based on evidence obtained from studies on patients with symptomatic disease, and surgery is not always indicated. Other patients are unable to undergo surgery, and thus a medical treatment is warranted. This systematic review provides an overview of the existing literature on contemporary pharmaceutical options available for the medical management of primary hyperparathyroidism.

METHODS

Databases of medical literature were searched for articles including terms for primary hyperparathyroidism and each of the included drugs. Data on s-calcium, s-parathyroid hormone, bone turnover markers, bone mineral density (BMD) and hard endpoints were extracted and tabulated, and level of evidence was determined. Changes in s-calcium were estimated and a meta-regression analysis was performed.

RESULTS

The 1,999 articles were screened for eligibility and 54 were included in the review. Weighted mean changes calculated for each drug in s-total calcium (mean change from baseline ± SEM) were pamidronate (0.31 ± 0.034 mmol/l); alendronate (0.07 ± 0.05 mmol/l); clodronate (0.20 ± 0.040 mmol/l); mixed bisphosphonates (0.16 ± 0.049 mmol/l); and cinacalcet (0.37 ± 0.013 mmol/l). The meta-analysis revealed a significant decrease of effect on s-calcium with time for the bisphosphonates (Coef. -0.049 ± 0.023, p = 0.035), while cinacalcet proved to maintain its effect on s-calcium over time. Bisphosphonates improved BMD while cinacalcet had no effect.

DISCUSSION

The included studies demonstrate advantages and drawbacks of the available pharmaceutical options that can prove helpful in the clinical setting. The great variation in how primary hyperparathyroidism is manifested requires that management should rely on an individual evaluation when counseling patients. Combining resorptive agents with calcimimetics could prove rewarding, but more studies are warranted.

Parathyromatosis: a rare yet problematic etiology of recurrent and persistent hyperparathyroidism

Recurrent or persistent hyperparathyroidism is an uncommon yet challenging clinical problem, and parathyromatosis is one of its very rare causes. In this minireview, we review causes of recurrent hyperparathyroidism and all cases of parathyromatosis available in the literature. The clinical course of a case of parathyromatosis with the longest follow-up (1977-2011) is described. Similar cases reported between 1975 and the present are reviewed and analyzed to characterize the clinical presentation, course, and management of this rare condition. Parathyromatosis, which is benign parathyroid tissue seeding, has been detailed in 35 patients in the English literature. The majority were female subjects, with end-stage renal disease, in their fifth to sixth decade of life. In most cases, the diagnosis was made intraoperatively; and the condition was often refractory to surgery. A calcimimetic agent was used in 5 cases with end-stage renal disease; serum calcium and/or parathyroid hormone levels decreased in 4 subjects, but only one was reported to experience increments in bone density. Medical management combining a calcimimetic with a bisphosphonate may therefore be a preferred alternative.

Long-term effects of neridronate and its discontinuation in patients with primary hyperparathyroidism

In patients with primary hyperparathyroidism (PHPT) not suitable for surgical correction, a skeletal protection with bisphosphonates is considered a reasonable option, but the long-term effects after treatment discontinuation are not well known. Sixty postmenopausal women with PHPT were given 400-600 IU vitamin D(3) daily and 100 mg neridronate IV every 2 months for 2 years with 2 additional years of follow-up without antiresorptive therapies. Bone mineral density (BMD) progressively rose by 6.7 ± 7.6% (SD) and by 2.9 ± 4.5% at the spine and femoral neck, respectively. During follow-up, mean BMD progressively fell, but after 2 years it was still 3.9 ± 5.5% higher than baseline values at the spine. Bone alkaline phosphatase and serum C-telopeptide of type I collagen decreased significantly within 6 months (28 and 49% versus baseline, respectively) and rose to baseline values within 6-12 months during follow-up. Serum PTH significantly rose from baseline during treatment, but it remained significantly higher than baseline during follow-up. The PTH changes were significantly correlated with serum 25-hydroxyvitamin D (25OHD) levels. In conclusion, in this study we observed that in patients with mild PHPT treatment with bisphosphonates is associated with the expected changes in bone-turnover markers and that the significant increases of both hip and spine BMD are partially maintained for at least 2 years after treatment discontinuation at the vertebral site. The marked increases in serum PTH levels, particularly in subjects with low 25OHD levels, persist after treatment discontinuation and this raises the suspicion that this might reflect a worsening of PHPT.

Medical management of asymptomatic primary hyperparathyroidism: proceedings of the third international workshop

BACKGROUND

Primary hyperparathyroidism (PHPT) is a common endocrine disorder that is frequently asymptomatic. The 2002 International Workshop on Asymptomatic PHPT addressed medical management of asymptomatic PHPT and summarized the data on nonsurgical approaches to this disease. At the Third International Workshop on Asymptomatic PHPT held in May 2008, this subject was reviewed again in light of data that have since become available. We present the results of a literature review of advances in the medical management of PHPT.

METHODS

A series of questions was developed by the International Task Force on PHPT. A comprehensive literature search for relevant studies evaluating the management of PHPT with bisphosphonates, hormone replacement therapy, raloxifene, and calcimimetics was conducted. Existing guidelines and recent unpublished data were also reviewed. All selected relevant articles were reviewed, and the questions developed by the International Task Force were addressed by the Consensus Panel.

RESULTS

Bisphosphonates and hormone replacement therapy are effective in decreasing bone turnover in patients with PHPT and improving bone mineral density (BMD). Fracture data are not available with either treatment. Raloxifene also lowers bone turnover in patients with PHPT. None of these agents, however, significantly lowers serum calcium or PTH levels. The calcimimetic cinacalcet reduces both serum calcium and PTH levels and raises serum phosphorus. Cinacalcet does not, however, reduce bone turnover or improve BMD.

CONCLUSIONS

Bisphosphonates and hormone replacement therapy provide skeletal protection in patients with PHPT. Limited data are available regarding skeletal protection in patients with PHPT treated with raloxifene. Calcimimetics favorably alter serum calcium and PTH in PHPT but do not significantly affect either bone turnover or BMD. Medical management of asymptomatic PHPT is a promising option for those who are not candidates for parathyroidectomy.

Parathyroid hormone activates PKC-delta and regulates osteoblastic differentiation via a PLC-independent pathway

PTH exerts major effects upon bone by activating PTH/PTHrP receptors (PTH1Rs) expressed on osteoblasts. The PTH1R is capable of engaging multiple signaling pathways in parallel, including Gs/adenylyl cyclase (AC), Gq/phospholipase C/protein kinase C (PLC/PKC) and a distinct mechanism, involving activation of PKC via a PLC-independent pathway, that depends upon ligand determinants within the PTH(29-34) sequence. The involvement of PLC-dependent vs. PLC-independent PKC activation in PTH action was studied in clonal PTH1R-expressing murine calvarial osteoblasts ("Wt9") using two signal-selective analogs, [G1,R19]hPTH(1-28) and [G1,R19]hPTH(1-34). Both analogs lack PLC signaling but differ in their capacity to activate the PLC-independent PKC pathway. Both hPTH(1-34) and [G1,R19]hPTH(1-34), but not [G1,R19]hPTH(1-28), increased differentiation of Wt9 cells during a 16-day alternate-daily treatment protocol. Wt9 cells expressed PKC-betaI, -delta, -epsilon and -zeta, none of which exhibited net translocation to membranes in response to hPTH(1-34) or either analog. hPTH(1-34) induced activation of membrane-associated PKC-delta, however, and a time- and concentration-dependent increase in cytosolic [phospho-Thr505]PKC-delta which was maximal within 40 s at 100 nM in both Wt9 cells and primary osteoblasts. This response was mimicked by [G1,R19]hPTH(1-34) but not by [G1,R19]hPTH(1-28). Increased expression of bone sialoprotein (BSP) and osteocalcin (OC) mRNAs induced by PTH(1-34) and [G1,R19]hPTH(1-34) in Wt9 cells was blocked by rottlerin, a PKC-delta inhibitor. We conclude that PTH1Rs activate PKC-delta by a PLC-independent, PTH(29-34)-dependent mechanism that promotes osteoblastic differentiation.

A single bisphosphonate infusion is associated with improved functional capacity in elderly subjects with primary hyperparathyroidism

BACKGROUND AND AIMS

Neuromuscular symptoms are frequent features of primary hyperparathyroidism in elderly patients. Whether these symptoms are related to concomitant disorders or to hypercalcemia is of major importance in selecting patients who could benefit by parathyroidectomy. To address this hypothesis, we investigated the effects of transient normalization of calcemia on functional capacity by the administration of a single infusion of the bone resorption inhibitors pamidronate or clodronate.

METHODS

Functional capacity was evaluated by the functional independence measure (FIM) in 25 patients aged 87.1+/-0.8 years (means+/-SEM) with primary hyperparathyroidism. Nine patients aged 88.4+/-1.1 with primary hyperparathyroidism, not receiving any bisphosphonate, were used as controls.

RESULTS

By inhibiting bone resorption, bisphosphonate administration caused transient normalization of calcemia, associated with improved FIM, at a significantly higher level than in untreated patients (+16.1+/-6.0 vs +4.2+/-3.2%, p<0.05).

CONCLUSIONS

If confirmed in a randomized prospective study, these results indicate that a single bisphosphonate infusion, with consecutive transient improvement of functional capacity in relation to plasma calcium normalization, could help in identifying elderly patients who would benefit by parathyroidectomy.

Update on genetic and clinical aspects of primary hyperparathyroidism

Primary hyperparathyroidism (pHPT) is a common endocrine disorder that predominantly affects postmenopausal women. It is mostly caused by solitary tumours within the parathyroid glands. Although the pathophysiology of pHPT is still incompletely understood, recent studies provide new clues on the development and cellular growth of tumours within the parathyroids associated with hypersecretion of parathyroid hormone and hypercalcaemia. The natural course of pHPT is rather benign. Nowadays, it has become an oligo- or asymptomatic disease often only detected by routine blood tests. These facts raise the question whether to perform parathyroidectomy on oligo- and asymptomatic patients with pHPT or whether it is possible to monitor these patients without surgery. The aim of this article is to review the literature as regards (i) the pathophysiological mechanisms that underlie parathyroid neoplasia and (ii) the defective calcium-sensing in patients with pHPT (iii) environmental and/or genetic risk factors that predispose to or promote parathyroid neoplasia, as well as (iv) alternative approaches to treat oligo- and asymptomatic patients with pHPT medically.

Primary hyperparathyroidism in an elderly woman: surgical reversibility of profound mental state problems due to mild hypercalcaemia

BACKGROUND

Clinical case of primary hyperparathyroidism in an 89 year old woman causing profound neuropsychiatric symptoms associated with relatively mild increases in serum calcium levels.

OBJECTIVES

To demonstrate that lowering of serum calcium levels by medical treatment (biphosphonate), provided a scientific basis from which to treat a very elderly woman with neuropsychiatric symptoms with definitive surgery.

METHOD

Case report.

RESULTS

The use of biphosphonate therapy led to marked but temporary improvements in her mental state.

CONCLUSION

A trial of reducing serum calcium levels with biphosphonate appears to be indicated in elderly patients with mild primary hyperparathyroidism and neuropsychiatric disorders.

Effects of oral alendronate in elderly patients with osteoporosis and mild primary hyperparathyroidism

In a large proportion of the patients with primary hyperparathyroidism (PHPT), a variable degree of osteopenia is the only relevant manifestation of the disease. Low bone mineral density (BMD) in patients with PHPT is an indication for surgical intervention because successful parathyroidectomy results in a dramatic increase in BMD. However, low BMD values are almost an invariable finding in elderly women with PHPT, who are often either unwilling or considered unfit for surgery. Bisphosphonates are capable of suppressing parathyroid hormone (PTH)-mediated bone resorption and are useful for the prevention and treatment of postmenopausal osteoporosis. In this pilot-controlled study, we investigated the effects of oral treatment with alendronate on BMD and biochemical markers of calcium and bone metabolism in elderly women presenting osteoporosis and mild PHPT. Twenty-six elderly patients aged 67-81 years were randomized for treatment with either oral 10 mg alendronate on alternate-day treatment or no treatment for 2 years. In the control untreated patients a slight significant decrease was observed for total body and femoral neck BMD, without significant changes in biochemical markers of calcium and bone metabolism during the 2 years of observation. Urine deoxypyridinoline (Dpyr) excretion significantly fell within the first month of treatment with alendronate, while serum markers of bone formation alkaline phosphatase and osteocalcin fell more gradually and the decrease became significant only after 3 months of treatment; thereafter all bone turnover markers remained consistently suppressed during alendronate treatment. After 2 years in this group we observed statistically significant increases in BMD at lumbar spine, total hip, and total body (+8.6 +/- 3.0%, +4.8 +/- 3.9%, and +1.2 +/- 1.4% changes vs. baseline mean +/- SD) versus both baseline and control patients. Serum calcium, serum phosphate, and urinary calcium excretion significantly decreased during the first 3-6 months but rose back to the baseline values afterward. Increase in serum PTH level was statistically significant during the first year of treatment. These preliminary results may make alendronate a candidate as a supportive therapy in patients with mild PHPT who are unwilling or are unsuitable for surgery, and for whom osteoporosis is a reason of concern.

Skeletal effects of primary hyperparathyroidism

OBJECTIVE

To review the effect of primary hyperparathyroidism on bone mass and occurrence of fractures as well as the advances in medical management of this relatively common condition.

METHODS

We conducted a MEDLINE search of peer-reviewed publications for the period from 1960 to 1999. Studies reviewed were those that evaluated bone mass and fracture risk in primary hyperparathyroidism in both male and female populations. Studies that assessed intervention with hormone replacement therapy, bisphosphonates, calcimimetic agents, and surgical treatment and their effect on bone mass and fracture were also reviewed. Preference was given to prospective studies, but retrospective, cross-sectional, and case-control studies were also evaluated.

RESULTS

Most densitometry studies completed to date have been limited by their design. Some cross-sectional studies that used both single-photon absorptiometry and dual-energy x-ray absorptiometry have demonstrated preferential bone loss at cortical skeletal sites. Bone density seems to be relatively well preserved at cancellous bone sites. The absence of large prospective controlled trials makes it difficult to evaluate fracture incidence associated with hyperparathyroidism. Retrospective and case-control studies have found conflicting results relative to fracture incidence in patients with primary hyperparathyroidism. Parathyroidectomy has been shown to be of value in improving bone mineral density at both the lumbar spine and the femoral neck. Hormone replacement therapy in postmenopausal women with primary hyperparathyroidism has also been effective in improving bone mineral density and decreasing bone turnover. Bisphosphonates are currently being evaluated for effectiveness in improving bone mineral density and reducing the risk of fracture. Early results with alendronate treatment have demonstrated improvements in bone mass. Calcimimetic agents are a new treatment option that may become useful in the medical management of primary hyperparathyroidism.

CONCLUSION

Although conflicting findings have been reported, bone loss has been noted in patients with primary hyperparathyroidism, especially at cortical skeletal sites. Medical management does not seem to be associated with increased morbidity or mortality in patients with asymptomatic primary hyperparathyroidism. Bone densitometry is advised, particularly for monitoring of bone mass at the midradius or femoral neck, in patients with primary hyperparathyroidism.

Medical approaches to primary hyperparathyroidism

Medical therapy is useful in cases of acute primary hyperparathyroidism, patients with recurrent disease, and parathyroid carcinoma. Among the therapeutic agents that have been employed, oral phosphate, bisphosphonates, and estrogens have been successful. The newly described calcimimetic agents directly block secretion of parathyroid hormone from the glands and offer an important new approach to medical therapy of primary hyperparathyroidism.

Phosphate depletion in the rat: effect of bisphosphonates and the calcemic response to PTH

BACKGROUND

The removal of phosphate from the diet of the growing rat rapidly produces hypercalcemia, hypophosphatemia, hypercalciuria, and hypophosphaturia. Increased calcium efflux from bone has been shown to be the important cause of the hypercalcemia and hypercalciuria. It has been proposed that the increased calcium efflux from bone is osteoclast mediated. Because bisphosphonates have been shown to inhibit osteoclast-mediated bone resorption, this study was performed to determine whether bisphosphonate-induced inhibition of osteoclast function changed the biochemical and bone effects induced by phosphate depletion.

METHODS

Four groups of pair-fed rats were studied: (a) low-phosphate diet (LPD; phosphate less than 0.05%), (b) LPD plus the administration of the bisphosphonate Pamidronate (APD; LPD + APD), (c) normal diet (ND, 0.6% phosphate), and (d) ND + APD. All diets contained 0.6% calcium. A high dose of APD was administered subcutaneously (0.8 mg/kg) two days before the start of the study diet and on days 2, 6, and 9 during the 11 days of the study diet. On day 10, a 24-hour urine was collected, and on day 11, rats were either sacrificed or received an additional APD dose before a 48-hour parathyroid hormone (PTH) infusion (0.066 microgram/100 g/hr) via a subcutaneously implanted miniosmotic pump.

RESULTS

Serum and urinary calcium were greater in the LPD and LPD + APD groups than in the ND and ND + APD groups [serum, 11.12 +/- 0.34 and 11.57 +/- 0.45 vs. 9.49 +/- 0.17 and 9.48 +/- 0.15 mg/dl (mean +/- SE), P < 0.05; and urine, 8.78 +/- 2.74 and 16.30 +/- 4.68 vs. 0.32 +/- 0.09 and 0.67 +/- 0.28 mg/24 hr, P < 0.05]. Serum PTH and serum and urinary phosphorus were less in the LPD and LPD + APD than in the ND and ND + APD groups (P < 0.05). The calcemic response to PTH was less (P < 0.05) in the LPD and LPD + APD groups than in the ND group and was less (P = 0.05) in the LPD + APD than in the ND + APD group. Bone histology showed that phosphate depletion increased the osteoblast and osteoclast surface, and treatment with APD reduced the osteoblast surface (LPD vs. LPD + APD, 38 +/- 4 vs. 4 +/- 2%, P < 0.05, and ND vs. ND + APD, 20 +/- 2 vs. 5 +/- 2%, P < 0.05) and markedly altered osteoclast morphology by inducing cytoplasmic vacuoles.

CONCLUSIONS

(a) Phosphate depletion induced hypercalcemia and hypercalciuria that were not reduced by APD administration. (b) The calcemic response to PTH was reduced in phosphate-depleted rats and was unaffected by APD administration in normal and phosphate-depleted rats, and (c) APD administration markedly changed bone histology without affecting the biochemical changes induced by phosphate depletion.

Primary Hyperparathyroidism: Diagnosis and Management

OBJECTIVE

To review the manifestations of primary hyperparathyroidism and the available treatment strategies.

METHODS

The epidemiologic and pathologic features of this endocrine disorder are outlined. Guidelines for surgical intervention are discussed, and the effectiveness of various medical treatments is summarized.

RESULTS

Primary hyperparathyroidism, a common disorder, is diagnosed on the basis of hypercalcemia in the presence of increased parathyroid hormone levels as measured by immunoassay. Clinical manifestations are variable with many patients being asymptomatic at the time of diagnosis. Patients with severe disease require definitive surgical treatment. Surgical cure rates are high--approximately 95% in experienced hands. Indications for surgery include a serum calcium of more than 2.9 mmol/L (12 mg/dL), osteoporosis, recurrent renal stones, and parathyroid carcinoma. As well, it is recommend in individuals younger than 50 years of age. Patients with mild disease may have a benign natural history and may not have progression to severe disease. Asymptomatic individuals with mild hypercalcemia and close to normal bone mass and renal function may be managed medically, particularly those who are over the age of 50 years. Medical management includes ensuring adequate hydration and avoiding volume depletion. Estrogen therapy is valuable in postmenopausal women without contraindications to hormone replacement. Calcitonin has been shown to decrease serum calcium levels on a short-term basis. Bisphosphonates are also potential treatment options and require further study. Calcium-mimetic agents also may become valuable in the medical management of primary hyperparathyroidism in the near future.

CONCLUSION

As primary hyperparathyroidism is being increasingly detected at an asymptomatic stage, medical therapy is assuming a greater role in the effective management of this common condition.

Cyclical etidronate and calcium carbonate (with citrate) supplementation for osteoporosis unmasking primary hyperparathyroidism

An 88 year old lady undergoing cyclical etidronate and calcium carbonate (with citrate) therapy for vertebral osteoporosis was found to be symptomatically hypercalcaemic at the end of the first cycle of treatment. She had been previously asymptomatic and normocalcaemic, but was subsequently found to have primary hyperparathyroidism. This condition is most prevalent in postmenopausal females--the same patient group at risk of osteoporosis. Serum calcium should be measured after commencing cyclical etidronate and calcium carbonate. If hypercalcaemia is detected primary hyperparathyroidism should be excluded as an underlying, cause.

Effect of bisphosphonate therapy and parathyroidectomy on the urinary excretion of galactosylhydroxylysine in primary hyperparathyroidism

BACKGROUND

In patients with mild or asymptomatic primary hyperparathyroidism a reliable index of bone resorption might be useful for appropriate management. Hydroxyproline is the most commonly used marker of bone resorption but its low specificity and sensitivity are known. Galactosylhydroxylysine, an amino acid mainly represented in bone collagen, has been proposed as a more suitable index of bone resorption. In this study we evaluated the sensitivity of galactosylhydroxylysine and hydroxyproline assays in following the changes of their urinary levels in 12 patients with mild primary hyperparathyroidism before and after treatment with bisphosphonate and surgery.

METHODS

Serum and fasting urine specimens were obtained from 12 women with mild primary hyperparathyroidism before and after bisphosphonate treatment (2.5 mg daily for 5 days, intravenously) and after a further 25 days; in 7 patients biochemical tests were also performed 1 and 6 days after parathyroidectomy. Galactosylhydroxylysine was assayed by an HPLC method and hydroxyproline by a RIA commercial kit.

RESULTS

Baseline galactosylhydroxylysine urinary levels were far above the normal range in all the patients whilst in 8 of them baseline hydroxyproline levels were normal. Bisphosphonate treatment significantly decreased bone turnover as shown by a significant fall in serum calcium (from 2.9 to 2.6 mmol/l; P < 0.001) and in galactosylhydroxylysine and hydroxyproline (-55 and -31% respectively). Twenty-five days after the end of treatment, resorption increased again and serum calcium and galactosylhydroxylysine, but not hydroxyproline, rose significantly towards basal levels. One day after parathyroidectomy serum calcium, galactosylhydroxylysine and PTH showed reduction below normal ranges. PTH and galactosylhydroxylysine returned to normal values at day 6 after parathyroidectomy. No changes in hydroxyproline levels were seen. Galactosylhydroxylysine, but not hydroxyproline, correlated significantly with serum calcium and PTH.

CONCLUSION

Galactosylhydroxylysine appears to be a sensitive index of bone resorption, useful in the clinical assessment of bone involvement and in the management of patients with mild primary hyperparathyroidism.

Decrease of serum calcium concentration and lost influence of calcium on parathyroid hormone release in a patient with primary hyperparathyroidism after treatment with diphosphonates

Prolonged decrease of elevated serum calcium levels after treatment with diphosphonates in patients with primary hyperparathyroidism (pHPT) is very rare. A patient with water clear cell hyperplasia and five enlarged glands is presented who received diphosphonates (day 1 through day 8 dichloromethylene diphosphonate orally and a single dose of 60 mg pamidronate on day 8 intravenously) leading to a significant fall in serum calcium levels. Surprisingly, there was no reactive increase in intact parathyroid hormone (PTH) in the following 18 days. Patients with missing PTH regulation to hypocalcemia after diphosphonates who need a period of stabilization prior to parathyroid surgery might benefit most from this therapy.

Medical management of asymptomatic primary hyperparathyroidism

Patients with mild asymptomatic primary hyperparathyroidism who do not meet currently accepted guidelines for surgery may be followed medically. General medical management of these individuals should be directed toward maintaining adequate hydration, therapy of hypertension, and avoiding immobilization. Diuretics should be used only with caution. Moderate dietary calcium intake (500-800 mg/day) should be encouraged. Propranolol and cimetidine are not useful in the therapy of primary hyperparathyroidism. Oral phosphate is efficacious in lowering serum and urinary calcium. However, because of concerns related to ectopic calcification, phosphate is usually reserved for those patients who meet surgical guidelines but who are not to undergo surgery. Bisphosphonates, potent inhibitors of osteoclast-mediated bone resorption, have been shown to lower serum and urinary calcium in patients with primary hyperparathyroidism. However, long-term data on their efficacy in this disorder are not yet available. The use of bisphosphonates at the present time is generally restricted to the research setting. More potent bisphosphonates as well as the design of newer agents that interfere with parathyroid hormone secretion may become very useful in future approaches to the medical management of primary hyperparathyroidism.