Diabetes mellitus with hyperparathyroidism: another indication for parathyroidectomy?

Association Between Primary Hyperparathyroidism and Secondary Diabetes Mellitus: Findings From a Scoping Review

An ill-defined association exists between diabetes mellitus (insulin resistance) and primary hyperparathyroidism. This article explores this phenomenon while providing an explanation for such a relationship and reviewing the evidence regarding the response to insulin sensitivity following a parathyroidectomy. Primary hyperparathyroidism may increase the risk of developing insulin resistance; peculiarly, this is not present in all patients. It is likely that both intracellular hypercalcemia and hypophosphatemia alter the insulin receptor expression and response; the contribution of parathyroid hormone is less clear. Following parathyroidectomy, patients may demonstrate improvement in their insulin sensitivity, while others have no response or a detrimental effect. A varied phenotype exists among patients, and furthermore, it is unclear why certain patients demonstrate improvement in insulin sensitivity following a parathyroidectomy, whereas others fail to do so. While this review provides a broad overview of the general endocrine community, it is imperative to note that clinical applicability is limited until further studies address these remaining uncertainties. Due to the lack of understanding regarding this endocrinological enigma, the presence of insulin resistance, at this present time, should not be a criterion for a parathyroidectomy.

The effect of surgery on fat mass, lipid and glucose metabolism in mild primary hyperparathyroidism

CONTEXT

Mild primary hyperparathyroidism has been associated with increased body fat mass and unfavorable cardiovascular risk factors.

OBJECTIVE

To assess the effect of parathyroidectomy on fat mass, glucose and lipid metabolism.

DESIGN, PATIENTS, INTERVENTIONS, MAIN OUTCOME MEASURES

119 patients previously randomized to observation (OBS; n = 58) or parathyroidectomy (PTX; n = 61) within the Scandinavian Investigation of Primary Hyperparathyroidism (SIPH) trial, an open randomized multicenter study, were included. Main outcome measures for this study were the differences in fat mass, markers for lipid and glucose metabolism between OBS and PTX 5 years after randomization.

RESULTS

In the OBS group, total cholesterol (Total-C) decreased from mean 5.9 (±1.1) to 5.6 (±1.0) mmol/L (P = 0.037) and LDL cholesterol (LDL-C) decreased from 3.7 (±1.0) to 3.3 (±0.9) mmol/L (P = 0.010). In the PTX group, the Total-C and LDL-C remained unchanged resulting in a significant between-group difference over time (P = 0.013 and P = 0.026, respectively). This difference was driven by patients who started with lipid-lowering medication during the study period (OBS: 5; PTX: 1). There was an increase in trunk fat mass in the OBS group, but no between-group differences over time. Mean 25(OH) vitamin D increased in the PTX group (P < 0.001), but did not change in the OBS group. No difference in parameters of glucose metabolism was detected.

CONCLUSION

In mild PHPT, the measured metabolic and cardiovascular risk factors were not modified by PTX. Observation seems safe and cardiovascular risk reduction should not be regarded as a separate indication for parathyroidectomy based on the results from this study.

Parathyroidectomy Ameliorates Glucose and Blood Pressure Control in a Patient with Primary Hyperparathyroidism, Type 2 Diabetes, and Hypertension

Effect of parathyroidectomy on glucose control and hypertension is controversial. Here, we report a case of a patient with primary hyperparathyroidism, type 2 diabetes mellitus, and hypertension in whom parathyroidectomy ameliorated both glucose control and blood pressure. Once high serum calcium levels were noticed, ultrasonography of neck confirmed a well-defined oval hypoechoic mass posterior to the right lobe of the thyroid, confirmed by scintiscan. Parathyroidectomy resulted in improvement of blood pressure and blood glucose. We could stop insulin and antihypertensive medications. We conclude that in patients with type 2 diabetes with vague complaints like fatigue, body ache, and refractory hypertension, as a part of the diagnostic workup, clinicians should also check serum calcium levels and parathyroid hormone to rule out hyperparathyroidism. Correction of hyperparathyroidism may result in improvement of hypertension and glucose control.

Cardiovascular risk factors in patients with asymptomatic primary hyperparathyroidism

OBJECTIVES

Patients with primary hyperparathyroidism (PHP), even asymptomatic, have an increased cardiovascular risk. However, data on reversibility or improvement of cardiovascular disorders with surgery are controversial. Our aims were to assess the prevalence of classic cardiovascular risk factors in patients with asymptomatic PHP, to explore their relationship with calcium and PTH levels, and analyze the effect of parathyroidectomy on those cardiovascular risk factors.

PATIENTS AND METHODS

A retrospective, observational study of two groups of patients with asymptomatic PHP: 40 patients on observation and 33 patients who underwent surgery. Clinical and biochemical data related to PHP and various cardiovascular risk factors were collected from all patients at baseline and one year after surgery in the operated patients.

RESULTS

A high prevalence of obesity (59.9%), type 2 diabetes mellitus (25%), high blood pressure (47.2%), and dyslipidemia (44.4%) was found in the total sample, with no difference between the study groups. Serum calcium and PTH levels positively correlated with BMI (r=.568, P=.011, and r=.509, P=.026 respectively) in non-operated patients. One year after parathyroidectomy, no improvement occurred in the cardiovascular risk factors considered.

CONCLUSIONS

Our results confirm the high prevalence of obesity, type 2 diabetes mellitus, high blood pressure, and dyslipidemia in patients with asymptomatic PHP. However, parathyroidectomy did not improve these cardiovascular risk factors.

Calcium and phosphate concentrations and future development of type 2 diabetes: the Insulin Resistance Atherosclerosis Study

AIMS/HYPOTHESIS

Low phosphate and high calcium concentrations have been linked to altered glucose tolerance and reduced insulin sensitivity in non-diabetic individuals. The aim of this study was to examine the relationships of calcium and phosphate levels and the calcium-phosphate product with the development of type 2 diabetes.

METHODS

Participants were 863 African-Americans, Hispanics and non-Hispanic whites in the Insulin Resistance Atherosclerosis Study who were free of diabetes at baseline. The mean follow-up period was 5.2 years. The insulin sensitivity index (SI) and acute insulin response (AIR) were directly measured using the frequently sampled IVGTT.

RESULTS

Calcium concentration (OR per 1 SD unit increase, 1.26 [95% CI 1.04, 1.53]) and calcium-phosphate product (OR 1.29 [95% CI 1.04, 1.59]) were associated with incident diabetes after adjustment for demographic variables, family history of diabetes, and 2 h glucose. The relationship between phosphate concentration and progression to diabetes was close to statistical significance (OR 1.21 [95% CI 0.98, 1.49]). Calcium concentration (OR 1.37 [95% CI 1.09, 1.72]) and calcium-phosphate product (OR 1.39 [95% CI 1.09, 1.77]) remained associated with incident diabetes after additional adjustment for BMI, plasma glucose, SI, AIR, C-reactive protein, estimated GFR, diuretic drugs and total calcium intake.

CONCLUSIONS/INTERPRETATION

Elevated serum calcium and calcium-phosphate product are associated with increased risk of developing type 2 diabetes independently of measured glucose, insulin secretion and insulin resistance. Future studies need to analyse the role of calcium-phosphate homeostasis in the pathophysiology of diabetes.

Serum calcium is positively correlated with fasting plasma glucose and insulin resistance, independent of parathyroid hormone, in male patients with type 2 diabetes mellitus

Patients with primary hyperparathyroidism have impaired glucose tolerance more often than do controls, and parathyroid resection sometimes improves this derangement. However, it is unclear whether serum calcium (Ca) or parathyroid hormone (PTH) is more strongly related to impaired glucose metabolism in subjects without primary hyperparathyroidism. In this cross-sectional study, we examined patients with type 2 diabetes mellitus (DM) (271 men and 209 women) and analyzed the relationships between serum concentrations of Ca or intact PTH and DM-related variables. Simple regression analyses showed that the level of serum Ca was significantly and positively correlated with the levels of fasting plasma glucose, immunoreactive insulin, and homeostasis model assessment insulin resistance in men (P < .05), but not in women. In contrast, intact PTH was not significantly correlated with DM-related parameters in either sex. Multiple regression analyses showed that the significant and positive correlations between serum Ca vs fasting plasma glucose and homeostasis model assessment insulin resistance in men still remained after adjustment for intact PTH as well as age, body weight, height, creatinine, albumin, phosphate, bone metabolic markers, and estradiol (P < .05). Serum Ca level is positively associated with impaired glucose metabolism, independent of PTH or bone metabolism, in men with type 2 DM.

Leptin: the link between overweight and primary hyperparathyroidism?

Primary hyperparathyroidism is one of the most common causes of hypercalcemia. Most cases result from sporadic benign monoclonal adenomas or hyperplasia. Increased body weight is consistently present in cohorts of patients with primary hyperparathyroidism. It has been shown that fat mass is the major determinant of serum parathyroid hormone levels independent of vitamin D status. Leptin, an adipocyte-derived hormone with mitogenic activity, regulates energy homeostasis and mineral metabolism. Serum leptin levels increase in parallel to the amount of adipose stores. Interestingly, a positive association between leptin and parathyroid hormone levels is observed. Patients with primary hyperparathyroidism have higher serum leptin levels than healthy subjects. In addition, leptin administration in mice increases circulating levels of parathyroid hormone. We hypothesize that leptin involves pathogenesis of primary hyperparathyroidism and represents a link between hyperparathyroidism and increased body weight.

Nonoperative management of primary hyperparathyroidism: the exception rather than the rule

The spectrum of classical primary hyperparathyroidism (pHPT) has expanded from a disabling disease to a largely asymptomatic one, leading to considerable uncertainty regarding which patients with pHPT will truly benefit from operative therapy. In the hands of an experienced endocrine surgeon, parathyroidectomy (PTx) is associated with a greater than 95% cure rate and long-term complication rates of less than 5%. We believe that all patients with pHPT should be referred to an experienced endocrine surgeon for consideration of PTx. Furthermore, our preference is to offer surgical intervention to all patients with pHPT who do not have prohibitive medical comorbidities. The purpose of this article is to outline the anticipated benefits of PTx in patients with nonclassical symptoms of pHPT with regard to improvement of the present condition, prevention of future complications or both.

Correlation between plasma calcium, parathyroid hormone (PTH) and the metabolic syndrome (MetS) in a community-based cohort of men and women

CONTEXT

In recent years, an association has been noted between several abnormalities that characterize the metabolic syndrome (MetS) and primary hyperparathyroidism (pHPT). These abnormalities include dyslipidaemia, obesity, insulin resistance and hypertension. The correlations between plasma calcium, parathyroid hormone (PTH) and the variables in the MetS in a normal population are still unclear.

OBJECTIVE

To describe correlations between plasma calcium and PTH and the various abnormalities present in the MetS in a healthy population.

DESIGN

We studied 1016 healthy individuals from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) population of 70 years old, by means of plasma analyses of calcium, PTH, creatinine, lipids, insulin and glucose, as well as by standardized blood pressure measurements. Further, body mass index (BMI) and waist circumference were determined.

RESULTS

The more National Cholesterol Education Program (NCEP) criteria for the MetS that were met, the higher the s-PTH and albumin-corrected s-calcium. Further, positive correlations between plasma calcium and BMI (P = 0.0003), waist circumference (P = 0.0009) and insulin resistance (P = 0.079) were found. PTH and BMI (P < 0.0001), waist circumference (P < 0.0001), systolic blood pressure (P = 0.0034), diastolic blood pressure (P = 0.0008), serum triglycerides (P = 0.0003) and insulin resistance (P = 0.0003) were positively correlated, whereas serum high density lipoproteins (HDL) (P = 0.036) and PTH were negatively correlated.

CONCLUSIONS

We conclude that PTH correlates with several of the metabolic factors included in the MetS within a normocalcaemic population. In addition, individuals with mild pHPT present significantly more NCEP criteria for MetS. We postulate that increased levels of PTH in pHPT may be associated with the increased cardiovascular morbidity and mortality seen in pHPT.

[Diagnostic evaluation and differential diagnosis of primary hyperparathyroidism]

Primary hyperparathyroidism (PHPT) is characterized by the autonomous production of parathyroid hormone (PTH), in which there is hypercalcemia or normal-high serum calcium levels, in the presence of elevated or inappropriately normal serum PTH concentrations. Exceptionally, in symptomatic patients, a diagnosis can be established on the basis of clinical data. PHPT must always be evaluated in patients with clinical histories of nephrolithiasis, nephrocalcinosis, osseous pain, subperiosteal resorption, and pathologic fractures, as well as in those with osteoporosis-osteopenia on dual-energy X-ray absorptiometry (DEXA), a personal history of neck irradiation, or a family history of multiple endocrine neoplasia syndrome (types 1 or 2). Diagnosis of PHPT is biochemical. Asymptomatic hypercalcemia (total serum calcium corrected by albumin), without guiding signs or symptoms, is the most frequent manifestation of the disease. For the differential diagnosis, PTH(1-84) must be measured, as well as phosphate, chloride, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and calcium-to-creatinine clearance. Suppressed or inappropriately low PTH1-84 guides the diagnose toward tumoral hypercalcemia and less frequently to granulomatous disease (sarcoidosis, tuberculosis, etc.), inadequate intake of 1alpha-hydroxyvitamin D or calcitriol, vitamin D or A intoxication, lithium intake, endocrinopathies (hyperthyroidism, Addison's disease, etc.) or treatment with thiazides, among other possibilities. Diagnosis of PHPT is confirmed by demonstrating persistent hypercalcemia (or normal-high serum calcium levels) in the presence of inappropriately normal or elevated serum PTH(1-84) concentrations, unless the urinary calcium-to-creatinine clearance ratio is lower than 0.01. In these cases, in the absence of thiazide intake or severe vitamin D deficiency, diagnosis should focus on benign familial hypercalcemic hypocalciuria. Parathyroid gland imaging is useful for localization of PHPT, but not for diagnosis of this entity.

Asymptomatic hyperparathyroidism--need for multicentre studies

Long-term follow-up is initially considered appropriate for the majority of patients with primary hyperparathyroidism (PHPT) having small increases in calcium levels (< 2.8 mmol/l) and lacking the 'classical' symptoms of PHPT. The supportive reasoning is that many such patients never progress to more severe biochemical or clinical disease. There are, however, arguments in favour of early surgical treatment of such patients but adequately powered studies have not been carried out in this subgroup of patients to asses the impact of PHPT on their quality of life, cardiovascular risk and bone density. Progressive loss in bone mineral density and an increased risk of bone fracture become increasingly significant in an ageing population. Left ventricular hypertrophy, an increased risk of arrhythmia and/or myocardial infarction in addition to changes in atherogenic lipid profile and impaired glucose tolerance may translate into an increased risk of premature death in this group of patients. Changes in the quality of life identified using standardized questionnaires are sometimes recognized by patients only in retrospect (i.e. after resolution of symptoms following successful parathyroidectomy). In addition, many series fail to assess and record accurately such symptoms. Multicentre cohort studies of patients with asymptomatic PHPT randomized to immediate or delayed surgical treatment could address some of the debated issues highlighted in this review. Until such studies are set up, most surgeons would consider that parathyroid surgery should represent the first choice of treatment for all patients, but many physicians would favour a long-term follow-up. Nevertheless, the threshold for referral for surgical treatment has been lowered since the introduction of scan-directed minimally invasive parathyroidectomy, which enables the experienced parathyroid surgeon to successfully treat patients with PHPT with a minimum of complications as a day-case operation. In the context of improved surgical treatment, we need more data on the benefits or otherwise in so-called asymptomatic patients with a thorough assessment of their bone quality, cardiovascular risk and quality of life.

Alanine to serine polymorphism at position 986 of the calcium-sensing receptor associated with coronary heart disease, myocardial infarction, all-cause, and cardiovascular mortality

BACKGROUND

Disorders of calcium homeostasis have been implicated in atherosclerosis. The calcium-sensing receptor (CASR) is crucial to the regulation of calcium metabolism. An alanine (A) to serine (S) polymorphism at codon 986 (A986S) of the CASR gene has been associated with higher calcium and osteoporosis; the association with coronary artery disease (CAD) has not been studied.

METHODS AND RESULTS

We investigated this polymorphism in individuals with CAD (n = 2561), including survivors of myocardial infarction (MI) (n = 1358) compared to 698 controls without angiographic CAD. Compared to AA homozygotes, the prevalence of CAD [multivariate odds ratio 1.25; 95% confidence interval (CI) 1.02-1.54] and previous MI (multivariate odds ratio 1.33; 95% CI 1.06-1.68) was increased in carriers of at least one S-allele. With each S-allele, the prevalence of CAD and MI increased 1.22-fold (95% CI 1.02-1.47) and 1.30-fold (95% CI 1.06-1.60), respectively. Fully adjusted hazard ratios for total and cardiovascular mortality per one S-allele were 1.24 (95% CI 1.05-1.46) and 1.38 (95% CI 1.13-1.67), respectively. In carriers of at least one S-allele, the adjusted hazard ratios for all-cause and cardiovascular death were 1.25 (95% CI 1.04-1.51) and 1.48 (95% CI 1.18-1.86), respectively. These associations were independent of cardiovascular risk factors, calcium and phosphate. The S-allele was associated with higher calcium (P < 0.001) and PTH (P < 0.02), and lower phosphate (P < 0.003) in CAD patients and controls.

CONCLUSION

Serine at position 986 of CASR may be an independent genetic predictor of angiographic CAD, previous MI, and cardiovascular mortality.

Primary hyperparathyroidism, insulin resistance, and cardiovascular disease: a review

The presentation of primary hyperthyroidism (PHPT) has changed substantially in the last decade. Before the introduction of routine calcium measurement in most automated biochemistry serum analyzers, it usually was diagnosed after renal and bony lesions already were present. Nowadays, its presentation is practically asymptomatic. Nevertheless, the cardiovascular morbidity and mortality of mild to moderate forms of PHPT reportedly are increasing. Individuals who have mild to moderate forms of PHPT have an increased risk for enduring cardiovascular disease, arterial hypertension, left ventricular hypertrophy, myocardial and valvular calcifications, altered vascular reactivity, and cardiac conduction. Finally, they also reveal alterations in carbohydrate metabolism, insulin resistance, dyslipidemia, and body composition.

National survey on the management of primary hyperparathyroidism by Swiss endocrinologists

BACKGROUND

From the endocrine surgeon's perspective, it is important to know how endocrinologists manage patients with primary hyperparathyroidism (pHPT). The aim of this survey was to evaluate the preoperative diagnostic workup and referral pattern for parathyroidectomy by Swiss endocrinologists.

MATERIALS AND METHODS

The survey was conducted by mailing a questionnaire to all members of the Swiss Society for Endocrinology and Diabetes in spring 2005.

RESULTS

The questionnaire was sent back by 68 of 124 endocrinologists (55%). The median annual case volume of patients with pHPT was 6 (range 1-50). The mean fraction of these patients referred for surgery was 59 +/- 24%. This fraction was significantly higher in the German-speaking part of Switzerland than in the French-speaking part (67 +/- 21% vs 51 +/- 27%). When considering surgery for asymptomatic pHPT, 62% of the endocrinologists rely routinely on the recommendations of the NIH consensus conference and 86% on the subsequent guidelines of the workshop in 2002. Sixty-seven percent of the endocrinologists routinely perform localization studies before possible referral for surgical exploration. Typically, they consisted of an ultrasonography of the neck (93%) and a (99m)Tc-MIBI scintigraphy (80%). The impact of the availability of a minimally invasive surgical procedure on the number of patients referred for surgery seems to be considerable. Sixty-one percent of the participants would expand the indication for surgery if the operation could be done by a limited surgical approach.

CONCLUSIONS

In a relevant fraction of patients with pHPT, endocrinologists still do not regard curative therapy as mandatory. Surprisingly, there are significant cultural differences concerning referral patterns to surgery between the German-speaking and the French-speaking parts of Switzerland. Minimally invasive procedures seem to lower the threshold for referral for surgical therapy.

Prevalence of glucose intolerance in primary hyperparathyroidism and the benefit of parathyroidectomy

BACKGROUND

Increased prevalence of diabetes mellitus (DM) in primary hyperparathyroidism (PHPT) is established, but not glucose intolerance (GI), nor benefit from parathyroidectomy on GI. We determined these during management of a continuous series of patients with PHPT routinely followed after surgery.

PATIENTS AND METHODS

WHO criteria classified 75 g oral glucose tolerance tests (OGTT) in 51/54 consecutively proven PHPT patients, into normal glucose tolerance (NGT), DM, impaired glucose tolerance (IGT) or impaired fasting glucose (IFG); GI was derived by adding those with DM and IGT/IFG. OGTT were repeated after parathyroidectomy (mean follow up 2.4 +/- SD 1.6 years). Paired student t tests were used to compare fasting and 2-h plasma glucose (PG).

RESULTS

At presentation 32/54 patients (59%) had NGT, 10 IGT/IFG (19%) and 12 type 2 DM (22%), nine newly diagnosed. Before parathyroidectomy 17/35 patients had NGT (49%), 18 GI (51%), 12 DM (34%) and 6 IGT/IFG (17%). Five out of six patients with IGT/IFG had NGT, one with NGT developed IGT. At completion 23 patients (66%) had NGT, 12 GI (34%), 4 IGT/IFG (11%) and 8 DM (23%). After parathyroidectomy fasting and 2-h. PG fell in 30/34 normocalcaemic patients not on hypoglycaemic agents, 5.6 +/- 1.0 to 5.4 +/- 0.8 mmol/l, 7.2 +/- 3.0 to 6.3 +/- 3.1 mmol/l (p < 0.05, p < 0.01).

CONCLUSIONS

1. At presentation with PHPT, OGTT commonly identifies Type 2 DM and GI.2. After successful parathyroidectomy fasting and 2-h. PG fall significantly (p < 0.05, p < 0.01). DM and IGT/IFG often ameliorates to IGT or NGT, persistently.

Mortality in sporadic primary hyperparathyroidism: nationwide cohort study of multiple parathyroid gland disease

BACKGROUND

The risk of dying from primary hyperparathyroidism (pHPT) is controversial and has been explored mainly in single parathyroid gland disease. The present study investigates mortality in pHPT due to multiple parathyroid gland disease.

METHODS

We used the nationwide Swedish In-patient Register and Cause-of-Death Registry to compare the mortality in 3485 Swedish patients subjected to parathyroidectomy during 1964 to 1999 with that of the Swedish population (standardized for age, gender, and calendar year). The patient cohort includes 36,596 person years.

RESULTS

Increased risk of death beyond the first postoperative year (standardized mortality ratio, 1.4; 95% CI, 1.37-1.52) was found in both sexes and for all age intervals below 80 years. The increased risk persisted more than 15 years postoperatively and related to cardiovascular diseases, diabetes mellitus, urogenital diseases, and malignant disorders. The increased risk of dying in cardiovascular diseases normalized during 1990 to 1999.

CONCLUSIONS

pHPT caused by multiple parathyroid gland enlargement is associated with an excessive mortality similar to pHPT of single parathyroid adenoma. The findings substantiate that modern modes of surgical treatment for pHPT normalize the risk of dying from cardiovascular complications and that the hyperpararthyroid state per se is the possible cause of the premature death.

Elevated sympathetic activity may promote insulin resistance syndrome by activating alpha-1 adrenergic receptors on adipocytes

An excess of free intracellular calcium can reduce the efficiency of insulin-mediated glucose transport by blocking the dephosphorylation of GLUT-4. Classical isoforms of protein kinase C (PKC) can interfere with insulin signalling via serine phosphorylation of IRS-1 and the insulin receptor. Parathyroid hormone (PTH), by activating phospholipase C-beta in adipocytes, can promote a sustained increase in intracellular free calcium in these cells, while also activating classical PKCs. This may rationalize the fact that insulin resistance is a typical feature of hyperparathyroidism, as well as epidemiological evidence that regular ingestion of dairy products or of ethanol--which down-regulates PTH secretion--reduces risk for insulin resistance syndrome and diabetes. Alpha-1 adrenergic receptors of adipocytes--like PTH receptors--also activate phospholipase C-beta, and thus have an effect analogous to PTH on intracellular free calcium and PKC activity in adipocytes. This suggests that, via activation of alpha-1 adrenergic receptors, increased sympathetic activity in adipose tissue may promote insulin resistance syndrome. In fact, measures which provoke increased sympathetic output--such as diuretic use and severe salt restriction--are known to compromise insulin sensitivity, whereas alpha-1 antagonist drugs, as well as drugs that act centrally to suppress sympathetic activity, typically have a favorable effect on insulin function. When insulin resistance syndrome is associated with elevated sympathetic activity--for example, in hypertensives who are obese or on diuretic therapy--measures which down-regulate sympathetic activity, or, more specifically, alpha-1 adrenergic activity, may be warranted. These include centrally acting imidazoline analogs (moxonidine, rilmenidine) and alpha-1 antagonists (doxazosin, prazosin). Taurine and high-dose pyridoxine may represent practical nutritional strategies for moderating elevated sympathetic activity, and exercise training and low-insulin-response diets may be useful in this regard as well.

A moderately low phosphate intake may provide health benefits analogous to those conferred by UV light - a further advantage of vegan diets

Although exposure to ultraviolet light is often viewed as pathogenic owing to its role in the genesis of skin cancer and skin aging, there is growing epidemiological evidence that such exposure may decrease risk for a number of more serious cancers, may have a favorable impact on blood pressure and vascular health, and may help to prevent certain autoimmune disorders - in addition to its well-known influence on bone density. Most likely, these health benefits are reflective of improved vitamin D status. Increased synthesis or intake of vitamin D can be expected to down-regulate parathyroid hormone (PTH), and to increase autocrine synthesis of its active metabolite calcitriol in certain tissues; these effects, in turn, may impact cancer risk, vascular health, immune regulation, and bone density through a variety of mechanisms. Presumably, a truly adequate supplemental intake of vitamin D - manyfold higher than the grossly inadequate current RDA - could replicate the benefits of optimal UV exposure, without however damaging the skin. Diets moderately low in bioavailable phosphate - like many vegan diets - might be expected to have a complementary impact on disease risks, inasmuch as serum phosphate suppresses renal calcitriol synthesis while up-regulating that of PTH. A proviso is that the impact of dietary phosphorus on bone health is more equivocal than that of vitamin D. Increased intakes of calcium, on the other hand, down-regulate the production of both PTH and calcitriol - the latter effect may explain why the impact of dietary calcium on cancer risk (excepting colon cancer), hypertension, and autoimmunity is not clearly positive. An overview suggests that a vegan diet supplemented with high-dose vitamin D should increase both systemic and autocrine calcitriol production while suppressing PTH secretion, and thus should represent a highly effective way to achieve the wide-ranging health protection conferred by optimal UV exposure.

PTH excess may promote weight gain by impeding catecholamine-induced lipolysis-implications for the impact of calcium, vitamin D, and alcohol on body weight

Increased free intracellular calcium ([Ca(2+)](i)) in adipocytes blunts the lipolytic response to catecholamines by activating phosphodiesterase 3B - the same enzyme that mediates the antilipolytic effect of insulin - while also compromising the efficiency of insulin-stimulated glucose uptake. Physiological increases in parathyroid hormone (PTH) have been shown to increase [Ca(2+)](i) in adipocytes. These considerations may rationalize recent evidence that high dietary intakes of calcium and/or dairy products may reduce risk for obesity, diabetes, and insulin-resistance syndrome, and they predict that other dietary measures which down-regulate PTH - such as good vitamin D status, and moderation in phosphate and salt intakes - may likewise be beneficial in these respects. Consistent with this position are reports that body weight is elevated in elderly subjects with both primary and secondary hyperparathyroidism; furthermore, insulin resistance is a well-known complication of both forms of hyperparathyroidism. The fact that regular alcohol consumption is associated with decreased PTH secretion may help to explain why moderate drinkers are less prone to insulin resistance, diabetes, and - in women - obesity. Down-regulation of PTH cannot be expected to promote dramatic weight loss, but in the long-term it may lessen risk for significant weight gain and diabetes, and conceivably may potentiate the fat loss achievable with caloric restriction and/or exercise.

Derangement of glucose metabolism in hyperparathyroidism

The derangement of glucose metabolism is found frequently in all forms of hyperparathyroidism. Both in primary (PHPT) and secondary hyperparathyroidism (SHPT) PTH excess is thought to be involved in deteriorating insulin sensitivity and secretion though their different clinical and pathophysiological conditions. In PHPT these abnormalities are related to a high frequency of Type 2 diabetes mellitus and also impaired glucose tolerance according to recent clinical studies, without differences between symptomatic and asymptomatic clinical presentation. In chronic renal failure (CRF), the disorders of glucose metabolism due to SHPT do not bear an increased risk for diabetes whereas they seem to be involved in the progression of atherosclerotic vascular damage which connotes CRF. Moreover, clinical and experimental studies have shown that vitamin D deficiency associated with glucose metabolism abnormalities favors the development of the metabolic syndrome. The potential for metabolic and cardiovascular harm related to hyperparathyroidism, especially PHPT, is the most interesting issue for clinical endocrinologists. This short review of the clinical and pathophysiological data of literature on glucose homeostasis disorders in hyperparathyroidism focuses on its potential clinical and therapeutic impact, particularly in the management of PHPT.

Impact of Hypercalcemia and Parathyroid Hormone Level on the Sensitivity of Preoperative Sestamibi Scanning for Primary Hyperparathyroidism

Technetium 99m sestamibi scanning (MIBI) can direct unilateral parathyroidectomy. However, the clinical application remains variable with sensitivities ranging from 55 to 100 per cent. We examined whether patient factors including serum calcium (Ca) and parathyroid hormone (PTH) levels impact the sensitivity of MIBI. We completed a retrospective review of 102 patients with primary hyperparathyroidism and mild hypercalcemia who underwent preoperative MIBI. All patients underwent bilateral neck explorations with abnormalities confirmed by histopathology. MIBI sensitivity was correlated with preoperative Ca and PTH levels using univariate and logistic regression analysis. The mean preoperative Ca was 11.0 mg/dL and the mean PTH was 158 pg/mL. More than 95 per cent of patients with Ca greater than 11.3 mg/dL had a positive scan as compared with 60 per cent of those with lesser values ( P = 0.0024). Similarly a serum PTH level greater than 160 pg/mL correlated with positive scans in 93 per cent as opposed to 57 per cent in those with lower levels ( P = 0.006). Using a scan-directed approach 65 of 74 patients would have undergone unilateral exploration; this would yield a 7.7 per cent operative failure rate because of contralateral multigland disease. Lower Ca and PTH levels seem to correlate with reduced sensitivity of MIBI. Increasing acceptance of surgery for hyperparathyroidism with minimal hypercalcemia may make MIBI less attractive without ancillary diagnostic measures such as rapid parathormone assays.

Coincident diabetes mellitus and primary hyperparathyroidism

The prevalence of diabetes mellitus in primary hyperparathyroidism is approximately 8% and that of primary hyperparathyroidism in diabetic patients is approximately 1%. Both values are about three-fold higher than the respective expected prevalences in general populations. Patients with both disorders are over 40 years of age and 80% are female; 22% have type 1 and 78% type 2 diabetes. Primary hyperparathyroidism presents first in approximately 20% of patients, and diabetes mellitus in 40%; both disorders present together, or within 1 year, in 40%. Approximately 40% of patients with primary hyperparathyroidism have impaired glucose tolerance. Insulin resistance is present in hyperparathyroidism and probably arises from a raised intracellular free calcium concentration which, by decreasing normal insulin-stimulated glucose transport, increases the requirement for insulin: if this insulin resistance progresses, impaired glucose tolerance and diabetes mellitus would result. Parathyroidectomy has been followed by regression of diabetes and of impaired glucose tolerance in some but not all patients. Early diagnosis of the second disorder is clinically desirable when one disorder is present. Hyperparathyroid patients should therefore be screened for impaired glucose tolerance and diabetes annually, and pre-operatively. Diabetic patients should be checked for hypercalcaemia at appropriate intervals; although only 1% of them may have hyperparathyroidism, this disorder if untreated is associated with hypertension, to which diabetic patients are already prone.

Hyperparathyroidism: the limits of surgery in cases of bone or cardiovascular involvement

In primary hyperparathyroidism (PHPT), asymptomatic bone disease can be detected by bone densitometry. The bone mineral density is about 10% lower than normal control values, especially in the cortical radius. Without parathyroidectomy, bone mineral density is frequently stable, but a few patients, mostly postmenopausal women, have a significant decrease. Histology shows maintenance of trabecular connectivity but with an increase in cortical porosity. After parathyroidectomy, bone mineral density increases, particularly at the lumbar spine and femoral neck, and the benefit persists after 10 years. The fracture risk is controversial but risk of trabecular bone fracture may be higher than that for controls. The impact of PHPT on survival is also controversial, but highest quartile of serum calcium, osteoporosis, old age, and low lean mass are each associated with a death risk. There is also a debate about the criteria for distinguishing between asymptomatic and symptomatic PHPT and about the bone mineral density threshold that should be used as a basis to recommend surgery. The rate of progression of PHPT is slow but in some cases bone loss progresses, justifying bone mineral density follow-up. The frequency of inadequate follow-up and the cost of nonoperative follow-up are in favor of recommending surgery. With broader indications for surgery, it is mandatory to improve the biochemical diagnosis of PHPT.