The relationship between serum TSH and bone mineral density in men and postmenopausal women: the Tromsø study

Frax score calculations in postmenopausal women with subclinical hypothyroidism

OBJECTIVE

The aim of our study was to evaluate the relationship between the elevated TSH and fracture risk in postmenopausal women with subclinical hypothyroidism for evaluation of individuals with a high risk for osteoporotic fractures.

DESIGN

FRAX score calculation (10-year estimated risk for bone fracture) and measurement of bone markers (osteocalcin and beta cross-laps) were performed in 82 postmenopausal women with newly discovered subclinical hypothyroidism (mean age 59.17±7.07, mean BMI 27.89±3.46kg/m2, menopause onset in 48.05±4.09 years of age) and 51 matched controls (mean age 59.69±5.72, mean BMI 27.68±4.66kg/m2, menopause onset in 48.53±4.58 years of age) with normal thyroid function.

RESULTS

The main FRAX score was significantly higher in the group with subclinical hypothyroidism than in the controls (6.50±4.58 vs. 4.35±1.56; p=0.001). Hip FRAX score was significantly higher in the group with subclinical hypothyroidism (1.11±1.94 vs. 0.50±0.46; p=0.030). There was no significant difference in bone markers: osteocalcin (23.99±12.63 vs. 21.79±5.34 ng/mL; p=0.484) and beta cross-laps (365.76±184.84 vs. 306.88±110.73 pg/mL; p=0.21) between the two groups.

CONCLUSIONS

Postmenopausal patients with subclinical hypothyroidism, in particular of autoimmune origin, have higher FRAX scores and a thus greater risk for low-trauma hip fracture than euthyroid postmenopausal women. Our results point to the need to monitor postmenopausal patients with subclinical hypothyroidism for avoidance of fractures.

Genetic confirmation for a central role for TNFα in the direct action of thyroid stimulating hormone on the skeleton

Clinical data showing correlations between low thyroid-stimulating hormone (TSH) levels and high bone turnover markers, low bone mineral density, and an increased risk of osteoporosis-related fractures are buttressed by mouse genetic and pharmacological studies identifying a direct action of TSH on the skeleton. Here we show that the skeletal actions of TSH deficiency are mediated, in part, through TNFα. Compound mouse mutants generated by genetically deleting the Tnfα gene on a Tshr(-/-) (homozygote) or Tshr(+/-) (heterozygote) background resulted in full rescue of the osteoporosis, low bone formation, and hyperresorption that accompany TSH deficiency. Studies using ex vivo bone marrow cell cultures showed that TSH inhibits and stimulates TNFα production from macrophages and osteoblasts, respectively. TNFα, in turn, stimulates osteoclastogenesis but also enhances the production in bone marrow of a variant TSHβ. This locally produced TSH suppresses osteoclast formation in a negative feedback loop. We speculate that TNFα elevations due to low TSH signaling in human hyperthyroidism contribute to the bone loss that has traditionally been attributed solely to high thyroid hormone levels.

A prospective study of thyroid function, bone loss, and fractures in older men: The MrOS study

Excess thyroid hormone is associated with increased bone loss and fracture risk in older women, but few data exist for men. We sought to determine if thyroid function is independently associated with bone loss and fracture risk in older men. Data were analyzed from the Osteoporotic Fractures in Men (MrOS) study, a cohort of community-dwelling U.S. men aged 65 years and older. Using a case-cohort design, fasting baseline serum archived at -80°C was assayed for thyroid-stimulating hormone (thyrotropin) (TSH) and free thyroxine (FT4) in 397 men with confirmed nonspine fracture, including 157 hip fractures, and 1420 randomly selected men without fracture. TSH and FT4 were analyzed as continuous variables and as thyroid function categories (subclinical hyperthyroid, euthyroid, and subclinical hypothyroid). Hip dual-energy X-ray absorptiometry (DXA) (Hologic QDR4500) was measured at baseline and after a mean follow-up of 4.6 years. Incident nonspine fractures were centrally adjudicated. Bone loss was evaluated with multivariate regression methods and fractures risk was evaluated using hazard models that accounted for the case-cohort sampling, adjusted for age, clinic-site, body mass index (BMI), race, physical activity, corticosteroid use, smoking, alcohol intake, and thyroid medication use. In fully adjusted analyses, TSH was not associated with risk of nonspine fracture (relative hazard [RH] 0.92 per SD decrease in TSH; 95% confidence interval [CI], 0.74-1.14), but was significantly associated with risk of hip fracture (RH 1.31; 95% CI, 1.01-1.71), which persisted among normal range TSH values (RH 1.21; 95% CI, 1.00-1.47). There was no association between TSH or FT4 and bone loss, and fracture risk did not differ significantly by thyroid function category. We conclude that although neither TSH nor FT4 are associated with bone loss, lower serum TSH may be associated with an increased risk of hip fractures in older men.

Thyroid-stimulating hormone is significantly associated with bone health status in men

BACKGROUND AND AIM

Recent studies revealed a novel association between thyroid-stimulating hormone (TSH) and bone health status in healthy male populations. The present study aimed to validate this association and provide new information on the relationship between TSH levels and calcaneal speed of sound (SOS) in men.

METHODS

This cross-sectional study recruited 681 men with complete data of calcaneal SOS, body anthropometry, serum TSH, free triiodothyronine (FT3) and free thyroxine (FT4) levels.

RESULTS

All subjects had FT3 and FT4 levels within the in-house reference range and 13 subjects had lower than normal TSH levels. The results revealed that the SOS value of subjects was significantly associated with TSH after multiple adjustments (p<0.05). When subjects were divided into quintiles according to their TSH levels, the difference of SOS between men with low-normal TSH and high-normal TSH contributed significantly to the association between TSH and bone health status (p<0.05). The significance of the association persisted with the inclusion and exclusion of subclinical hyperthyroid subjects.

CONCLUSIONS

There was a significant association between TSH levels and bone health status in men as assessed by quantitative ultrasound. This age-independent association between TSH and SOS might explain some of the individual variation of bone health status in men.

Metabolic and clinical consequences of hyperthyroidism on bone density

In 1891, Von Recklinghausen first established the association between the development of osteoporosis in the presence of overt hyperthyroidism. Subsequent reports have demonstrated that BMD loss is common in frank hyperthyroidism, and, to a lesser extent, in subclinical presentations. With the introduction of antithyroid medication in the 1940s to control biochemical hyperthyroidism, the accompanying bone disease became less clinically apparent as hyperthyroidism was more successfully treated medically. Consequently, the impact of the above normal thyroid hormones in the pathogenesis of osteoporosis may be presently underrecognized due to the widespread effective treatments. This review aims to present the current knowledge of the consequences of hyperthyroidism on bone metabolism. The vast number of recent papers touching on this topic highlights the recognized impact of this common medical condition on bone health. Our focus in this review was to search for answers to the following questions. What is the mechanisms of action of thyroid hormones on bone metabolism? What are the clinical consequences of hyperthyroidism on BMD and fracture risk? What differences are there between men and women with thyroid disease and how does menopause change the clinical outcomes? Lastly, we report how different treatments for hyperthyroidism benefit thyroid hormone-induced osteoporosis.

Bone health in children with long-term idiopathic subclinical hypothyroidism

Background

Subclinical hypothyroidism (SH) is a relatively common condition characterized by a mild persistent thyroid failure. The management of children with SH is still a controversial issue and the decision to treat with L-thyroxine represents a clinical dilemma. Thyroid hormone and TSH play an important role in skeletal growth and bone mineral homeostasis.

Aim

To evaluate whether untreated idiopathic SH may affect bone health in childhood and to compare two different diagnostic tools such as dual-energy X-ray densitometry (DXA) and quantitative ultrasound (QUS).

Patients and Methods

Twenty-five children and adolescents (11 males) aged 9.8 ± 3.5 years (range 4.2-18.7) with untreated idiopathic SH were enrolled in the study. SH was diagnosed on the basis of normal FT4 levels with TSH concentrations between 4.2 and 10 mU/l. Children have been followed for 3.3 ± 0.3 years from the time of SH diagnosis. Twenty-five healthy children, age- and sex-matched, were enrolled as controls. Patients and controls underwent DXA to evaluate lumbar spine bone mineral density (BMD) and QUS at proximal phalanges of the non-dominant hand to assess bone quality, measured as amplitude-dependent speed of sound (Ad-SoS) and bone transmission time (BTT).

Results

Mean BMD Z-score was −0.4 ± 1.36 in patients and −0.2 ± 1.2 in controls. Mean Ad-SoS Z-score was 0.01 ± 1.0 in patients and 0.1 ± 1.2 in controls and mean BTT Z-score was −0.03 ± 0.8 and 0.04 ± 1.1 respectively. All values were within the normal range, both in patients and in controls. There were no statistically significant differences between the two groups.

Conclusion

Bone health, evaluated by lumbar spine DXA and phalangeal QUS, is not impaired in our children, despite long-term duration of idiopathic SH. Data about bone status provided by QUS are comparable to those provided by DXA. Therefore, QUS may represent a good, cheaper and safe screening test for bone evaluation in children with SH.

Hyperthyroid-associated osteoporosis is exacerbated by the loss of TSH signaling

The osteoporosis associated with human hyperthyroidism has traditionally been attributed to elevated thyroid hormone levels. There is evidence, however, that thyroid-stimulating hormone (TSH), which is low in most hyperthyroid states, directly affects the skeleton. Importantly, Tshr-knockout mice are osteopenic. In order to determine whether low TSH levels contribute to bone loss in hyperthyroidism, we compared the skeletal phenotypes of wild-type and Tshr-knockout mice that were rendered hyperthyroid. We found that hyperthyroid mice lacking TSHR had greater bone loss and resorption than hyperthyroid wild-type mice, thereby demonstrating that the absence of TSH signaling contributes to bone loss. Further, we identified a TSH-like factor that may confer osteoprotection. These studies suggest that therapeutic suppression of TSH to very low levels may contribute to bone loss in people.

The skeletal consequences of thyrotoxicosis

Euthyroid status is essential for normal skeletal development and the maintenance of adult bone structure and strength. Established thyrotoxicosis has long been recognised as a cause of high bone turnover osteoporosis and fracture but more recent studies have suggested that subclinical hyperthyroidism and long-term suppressive doses of thyroxine (T4) may also result in decreased bone mineral density (BMD) and an increased risk of fragility fracture, particularly in postmenopausal women. Furthermore, large population studies of euthyroid individuals have demonstrated that a hypothalamic-pituitary-thyroid axis set point at the upper end of the normal reference range is associated with reduced BMD and increased fracture susceptibility. Despite these findings, the cellular and molecular mechanisms of thyroid hormone action in bone remain controversial and incompletely understood. In this review, we discuss the role of thyroid hormones in bone and the skeletal consequences of hyperthyroidism.

Subclinical thyroid disease

Subclinical thyroid diseases--subclinical hyperthyroidism and subclinical hypothyroidism--are common clinical entities that encompass mild degrees of thyroid dysfunction. The clinical significance of mild thyroid overactivity and underactivity is uncertain, which has led to controversy over the appropriateness of diagnostic testing and possible treatment. In this Seminar, we discuss the definition, epidemiology, differential diagnoses, risks of progression to overt thyroid disease, potential effects on various health outcomes, and management of subclinical hyperthyroidism and subclinical hypothyroidism. Treatment recommendations are based on the degree to which thyroid-stimulating hormone concentrations have deviated from normal and underlying comorbidities. Large-scale randomised trials are urgently needed to inform how to best care for individuals with subclinical thyroid disease.

Short-term and long-term orthopaedic issues in patients with fragility fractures

BACKGROUND

Patients with impaired bone quality who suffer a fragility fracture face substantial challenges in both their short- and long-term care. In addition to poor bone quality, many of these patients have multiple medical comorbidities that alter their surgical risk and affect their ultimate functional recovery. Some medical issues can contribute to the altered bone quality and must be addressed to prevent future fractures.

QUESTIONS/PURPOSES

This review summarizes the modifications in perioperative management and fracture fixation in patients with common fragility fractures who have impaired bone quality. It also summarizes the postoperative diagnosis and treatment of secondary causes of impaired bone quality in these patients.

METHODS

We performed a PubMed search, and literature published after 2000 was prioritized, with the exception of benchmark clinical trial studies published before 2000.

RESULTS

Patients with altered bone quality require rapid perioperative management of multiple medical comorbidities. Implant selection in patients with poor quality bone should permit early weightbearing, and constructs should maximize surface area contact with the remaining bone. Long-term diagnosis and treatment of other disease states contributing to poor bone quality (vitamin D deficiency/insufficiency, hypothyroidism, hyperthyroidism, hyperparathyroidism, Cushing's disease, and hypogonadism) must occur to minimize the chances of future fractures.

CONCLUSIONS

Recognition of patients with impaired bone quality and proper treatment of their special needs in both the short and long term are essential for their best opportunity for maximal functional recovery and prevention of future fractures.

Should we treat mild subclinical/mild hyperthyroidism? Yes

Whether or not subclinical hyperthyroidism (SCH) should be treated, remains a matter of debate because there are no randomized clinical trials answering the question if treatment improves long-term health outcomes. Cross-sectional and longitudinal population-based sudies demonstrate clear associations between SCH and risk on atrial fibrillation and fractures; associations with cardiovascular and overall mortality and mental health are less consistent. Associations with adverse outcomes of cardiovascular and bone health are in all likelihood causally related to SCH in view of an observed dose-response relationship and the existence of a plausible biologic mechanism. Short-term intervention studies show improvement of surrogate outcome measurements. Against this background treatment of both endogenous and exogenous SCH is recommended when TSH is 0.1 mU/l or lower. At TSH values>0.1-<0.4 mU/l treatment should be considered in the presence of risk factors (age>65 years, post menopause, osteoporosis, cardiac disease).

Thyroid disorders and bone mineral metabolism

Thyroid diseases have widespread systemic manifestations including their effect on bone metabolism. On one hand, the effects of thyrotoxicosis including subclinical disease have received wide attention from researchers over the last century as it an important cause of secondary osteoporosis. On the other hand, hypothyroidism has received lesser attention as its effect on bone mineral metabolism is minimal. Therefore, this review will primarily focus on thyrotoxicosis and its impact on bone mineral metabolism.

The relationship between thyroid function and bone mineral density in euthyroid healthy subjects in Taiwan

INTRODUCTION

It has been reported that low normal circulating thyrotropin (TSH) levels correlate with lower bone mineral density (BMD) in the Korean postmenopausal female. The goal of this study is to evaluate this relationship in different sex and age groups in a Chinese population.

MATERIALS AND METHODS

A total of 2,957 subjects in Taiwan, 1,343 males and 1,614 females, aged from 45 to 64 years, were enrolled in this study. They were divided into four groups: group 1 was males aged between 45 and 50 years (young male, YM); group 2 was females aged between 45 and 50 years (young female, YF); group 3 was males older than 50 years (old male, OM); and group 4 was females older than 50 years (old female, OF). Plasma total thyroxine (T4) and TSH were measured. BMD was quantified at the wrist using dual energy X-ray absorptiometry.

RESULTS

YM had the highest BMD whereas OF had the lowest BMD. Among the four groups, no significant correlation between TSH level and BMD was found in the four groups, but a significant negative correlation existed between T4 and BMD in OF (r = -0.089, p = 0.005) and YM (r = -0.109, p = 0.018).

CONCLUSION

Our study did not find significant correlations between TSH and BMD in both men and women with normal thyroid function in Taiwan. Weak negative correlations existed between T4 and BMD in postmenopausal women and young men. Further studies with measurement of FT4 and TSH and with a longitudinal design may shed light on this population difference.

The role of FSH and TSH in bone loss and its clinical relevance

Osteoporosis, a global health problem, is now frequently recognized to be secondary to alterations in the pituitary-bone axis. This review examines the current evidence for how dysregulation of the pituitary-bone axis leads to osteoporotic bone loss. Specifically, perimenopausal bone loss in the context of follicle-stimulating hormone action, and hyperthyroid bone loss in the context of thyroid-stimulating hormone action are explored. From the reviewed scientific findings, recommendations for early diagnosis and better clinical management of bone loss are made.

Subclinical thyroid disorders: significance and clinical impact

Subclinical thyroid diseases are defined by abnormal serum thyroid stimulating hormone (TSH) levels associated with normal thyroid hormone concentrations. The diagnosis of these conditions depends on defining the 'normal' euthyroid TSH range; in this review, arguments for and against lowering the upper limit of TSH are summarised. Although, subclinical hypothyroidism and subclinical hyperthyroidism are frequently encountered, their long-term consequences are debated due to conflicting results from many observational studies. The causes, effects and outcomes of treatment of both subclinical diseases are described, and the direction of future research in these conditions is outlined.

The association between serum thyrotropin (TSH) levels and bone mineral density in healthy euthyroid men

OBJECTIVE

Although osteoporosis is increasingly shown to occur in a considerable proportion of men, data on risk factors for male osteoporosis are limited. In this study, we investigated the association between serum thyrotropin (TSH) concentration and bone mineral density (BMD) in healthy euthyroid men. Design A cross-sectional community (health promotion centre)-based survey.

SUBJECTS AND MEASUREMENTS

For 1478 apparently healthy euthyroid men who participated in a routine health screening examination, we measured BMD at the lumbar spine and femoral neck using dual energy X-ray absorptiometry and serum TSH concentrations using immunoluminometry.

RESULTS

Lumbar spine BMD linearly increased with TSH level after adjustment for age, weight and height (P for trend = 0.002), and statistical significance persisted after additional adjustment for smoking and drinking habits (P for trend = 0.010). When serum alkaline phosphatase was added as a confounding variable, the relationship was still significant (P for trend = 0.016). Femoral neck BMD also tended to increase in higher TSH concentration after adjustment for age, weight and height (P for trend = 0.042), but this association disappeared after additional adjustment for smoking and drinking habits. The odds of lower BMD (i.e. osteopaenia and osteoporosis combined) were significantly increased in subjects with low-normal TSH (i.e. 0.4-1.2 mU/l), when compared to high-normal TSH (i.e. 3.1-5.0 mU/l), after adjustment for confounding factors (odds ratio = 1.45, 95% CI = 1.02-2.10).

CONCLUSION

These results suggest that a serum TSH concentration at the lower end of the reference range may be associated with low BMD in men.

Can bone loss be reversed by antithyroid drug therapy in premenopausal women with Graves' disease?

Context

Hyperthyroidism can lead to reduced bone mineral density (BMD) and increased fracture risk particularly in postmenopausal women, but the mechanism behind is still unclear.

Objective

Prospective examination of the influence of thyroid hormones and/or thyroid autoantibodies on BMD in premenopause.

Design

We have examined 32 premenopausal women with untreated active Graves' disease from time of diagnosis, during 18 months of antithyroid drug therapy (ATD) and additionally 18 months after discontinuing ATD. Variables of thyroid metabolism, calcium homeostasis and body composition were measured every 3 months. BMD of lumbar spine and femoral neck were measured at baseline, 18 ± 3 and 36 ± 3 months. Data were compared to base line, a sex- and age matched control group and a group of patients with Hashimoto's thyroiditis treated with non-suppressive doses of levothyroxine.

Results

The study showed significantly (p < 0.002) lower BMD in the thyrotoxic state compared to the control group with subsequent significant improvement during 18 ± 3 months of ATD compared to baseline (p < 0.001). However, during the following 18 months after stopping ATD femoral neck BMD decreased again unrelated to age (more than 0.4% per year, p < 0,002). The wellestablished effect of thyrotoxicosis on calcium homeostasis was confirmed. The positive predictor for best BMD was TSH receptor antibodies (TRAb) while free T4 correlated negatively in the thyrotoxic female Graves' patients (p < 0.02 and p < 0.003). In healthy controls and patients with treated Graves' disease both TSH and T4 correlated negatively to the bone mass (BMC) (p < 0.003).

Conclusion

The results indicated a clinically relevant impact of thyroid function on bone modulation also in premenopausal women with Graves' disease, and further indicated the possibility for a direct action of TRAb on bones.

Correlates of trabecular and cortical volumetric bone mineral density at the femoral neck and lumbar spine: the osteoporotic fractures in men study (MrOS)

The objective of this cross-sectional analysis was to examine the correlates of trabecular and cortical volumetric bone mineral density (vBMD) in 3670 community-dwelling men, mean age 73.6 ± 5.9 years. vBMD was measured by quantitative computed tomography (QCT) and areal BMD by dual-energy X-ray absorptiometry (DXA). Demographic, historical, and lifestyle information was obtained by interview, and height, weight, and neuromuscular function were determined by examination. To express the strength of the associations, percent differences (95% confidence interval) were calculated from multivariable linear regression models using the formula 100 (β × unit/mean BMD). Units for continuous variables were chosen to approximate 1 standard deviation (SD). The multivariable linear regression models predicted 15%, 21%, and 20% of the overall variance in trabecular and cortical vBMD of the femoral neck and vBMD of the lumbar spine, respectively. Diabetes was associated with a 16.5% greater trabecular vBMD at the femoral neck and 11% at the lumbar spine but less than 2% for cortical vBMD. For femoral neck trabecular vBMD, the strongest negative correlates were past smoking (-9%), fracture history (-15%), kidney stones (-7%), corticosteroids (-11%), and insulin therapy (-26%). For cortical vBMD, the strongest negative correlate was use of thyroid medication (-2.8%). The strongest negative correlates for lumbar spine trabecular vBMD were fracture history (-5%), antiandrogen use (-19%), height (-8%), and thiazoliainedione use (-22%). Bioavailable estradiol and testosterone levels were positively related and sex hormone-binding globulin was negatively related to trabecular vBMD of the spine. There was no relationship between sex hormones and femoral neck trabecular vBMD. Our conclusion is that correlates of trabecular vBMD and cortical vBMD appear to differ in older men.

Drug-induced osteoporosis in the older adult

The elderly population is at risk for polypharmacy and, therefore, also at risk for drug-induced osteoporosis (DIOP). Epidemiologic studies provide valuable information about medications that may place patients at risk for DIOP. While glucocorticoids are the most common cause of DIOP, the use of several other therapeutic agents can place patients at risk for significant bone loss and fracture. These medications include, but are not limited to, aromatase inhibitors, gonadotropin-releasing hormone agonists, thyroid replacement therapy, antiepileptics, antidepressants, antipsychotics, lithium, gastric acid lowering agents, thiazolidinediones, loop diuretics, heparins and warfarin, vitamin A and cyclosporine. This article provides information about their mechanism of action, studies that have evaluated these agents in DIOP and prevention and treatment strategies.

Thyroid function within the upper normal range is associated with reduced bone mineral density and an increased risk of nonvertebral fractures in healthy euthyroid postmenopausal women

CONTEXT

The relationship between thyroid function and bone mineral density (BMD) is controversial. Existing studies are conflicting and confounded by differences in study design, small patient numbers, and sparse prospective data.

OBJECTIVE

We hypothesized that variation across the normal range of thyroid status in healthy postmenopausal women is associated with differences in BMD and fracture susceptibility.

DESIGN

The Osteoporosis and Ultrasound Study (OPUS) is a 6-yr prospective study of fracture-related factors.

SETTING

We studied a population-based cohort from five European cities.

PARTICIPANTS

A total of 2374 postmenopausal women participated. Subjects with thyroid disease and nonthyroidal illness and those receiving drugs affecting thyroid status or bone metabolism were excluded, leaving a study population of 1278 healthy euthyroid postmenopausal women.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

We measured free T(4) (fT4) (picomoles/liter), free T(3) (fT3) (picomoles/liter), TSH (milliunits/liter), bone turnover markers, BMD, and vertebral, hip, and nonvertebral fractures.

RESULTS

Higher fT4 (beta = -0.091; P = 0.004) and fT3 (beta = -0.087; P = 0.005) were associated with lower BMD at the hip, and higher fT4 was associated with increasing bone loss at the hip (beta = -0.09; P = 0.015). After adjustment for age, body mass index, and BMD, the risk of nonvertebral fracture was increased by 20% (P = 0.002) and 33% (P = 0.006) in women with higher fT4 or fT3, respectively, whereas higher TSH was protective and the risk was reduced by 35% (P = 0.028). There were independent associations between fT3 and pulse rate (beta = 0.080; P = 0.006), increased grip strength (beta = 0.171; P<0.001), and better balance (beta = 0.099; P < 0.001), indicating that the relationship between thyroid status and fracture risk is complex.

CONCLUSIONS

Physiological variation in normal thyroid status is related to BMD and nonvertebral fracture.

New horizons in skeletal physiology and pathophysiology

OBJECTIVE

To review new discoveries that revisit our current thinking on the genesis of osteoporosis using hypogonadal and thyrotoxic bone loss as examples.

METHODS

We focus on cell biologic, mouse genetic, and human studies that have established a direct action of the interior pituitary hormones follicle-stimulating hormone and thyrotropin on the skeleton and discuss emerging clinical evidence for a novel pituitary-bone axis in humans that bypasses master endocrine organs, namely the ovaries and thyroid gland.

RESULTS

The cataloguing of human mutations, the use of genetically modified mice that recapitulate human disease, and the rapid growth of genomic sciences have together had a profound impact on how basic research is translated into clinical practice. The skeleton has become a paradigm for the application of such advances to an extent that hitherto unrecognized physiologic and pathophysiologic findings have emerged. We propose that hypogonadal and thyrotoxic bone loss are not solely due to changes in the level of master hormones, but instead also arise from the direct action of anterior pituitary hormones on the skeleton.

CONCLUSIONS

We predict a pituitary-bone axis in which pituitary hormones bypass traditional endocrine targets to affect the skeleton directly with remarkable sensitivity. New therapeutic targets thus become a likely possibility.

Serum TSH values and risk of vertebral fractures in euthyroid post-menopausal women with low bone mineral density

INTRODUCTION

There is evidence that variations of thyrotropin (TSH) even in its reference range may influence bone mineral density (BMD). In fact, low-normal TSH values have been associated with high prevalence of osteoporosis in post-menopausal women. However, data associating TSH and risk of fractures are scanty and limited to subjects with subclinical thyrotoxicosis.

MATERIALS AND METHODS

In this observational study, we investigated the correlation between serum TSH and prevalence of radiological vertebral fractures in a cohort of 130 post-menopausal women with normal thyroid function.

RESULTS

Osteoporosis was observed in 80 women (61.5%), whereas 49 women (37.7%) had osteopenia. Vertebral fractures were found in 49 women (37.7%), who were significantly older, with higher prevalence of osteoporosis and with lower serum TSH values as compared with women who did not fracture. Stratifying the patients according to serum TSH values, vertebral fractures were found to be significantly (p=0.004) more prevalent in first tertile (56.8%) of TSH values as compared with the second (23.3%) and third tertiles (32.6%). Multivariate logistic regression analysis demonstrated that low serum TSH maintained a significant correlation with vertebral fractures (odds ratio 2.8, C.I. 95% 1.20-6.79) even after correction for age, BMD, BMI and serum free-thyroxine values.

DISCUSSION

Low-normal TSH values are associated with high prevalence of vertebral fractures in women with post-menopausal osteoporosis or osteopenia, independently of thyroid hormones, age and BMD.

Role of the pituitary-bone axis in skeletal pathophysiology

PURPOSE OF REVIEW

Embedded within textbooks for decades is the hard fact that releasing hormones from the anterior pituitary, namely, follicle-stimulating hormone, thyroid-stimulating hormone and adrenocorticotropic hormone, stimulate master hormone secretion from target endocrine organs. We propose a paradigm shift in endocrine physiology, which is that these hormones act by design on bone directly, also now considered an endocrine organ.

RECENT FINDINGS

Complementary investigations using mouse genetic and cell biological approaches reveal that follicle-stimulating hormone and thyroid-stimulating hormone act on bone cells directly to regulate bone remodeling and bone mass. Thyroid-stimulating hormone inhibits bone remodeling, whereas follicle-stimulating hormone stimulates it. We also find that the posterior pituitary hormone oxytocin is anabolic to the skeleton.

SUMMARY

An ambitious extrapolation is that a plurality of pituitary hormones acts in concert as part of a 'pituitary-bone' axis to regulate skeletal integrity in health and disease. When dysregulated master hormone levels during hypogonadism and hyperthyroidism cause altered pituitary hormone secretion through hypothalamic feedback, the latter hormones contribute to the skeletal loss.

Phalangeal quantitative ultrasound and bone mineral density in evaluating cortical bone loss: a study in postmenopausal women with primary hyperparathyroidism and subclinical iatrogenic hyperthyroidism

Twenty-five postmenopausal women with primary hyperparathyroidism (PHPT) and 30 age-matched women with subclinical hyperthyroidism (sHTH) were studied to assess cortical bone loss. One hundred two healthy women were also recruited. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry at lumbar spine (LS), femoral neck (FN) and femoral total (FT), and at one-third of the radius (R). Amplitude-dependent speed of sound (ADSoS) and Ultrasound Bone Profile Index (UBPI) were also evaluated using phalangeal quantitative ultrasound (QUS). A significant correlation was found between QUS and BMD at LS (ADSoS, p < 0.05) and R (ADSoS and UBPI, p < 0.001) in controls. QUS significantly correlated with BMD at LS, FN (p < 0.01), and FT (p < 0.001) in sHTH. No correlations were found in the PHPT group. Mean T-score values of all parameters were significantly lower in patients compared with controls (p < 0.001); however, they did not differ between PHPT and sHTH patients. T-score of R, ADSoS, and UBPI was reduced compared with other sites (p < 0.001) in both diseases. In postmenopausal women with PHPT and sHTH, bone loss is mainly detectable at cortical level. However, qualitative and/or structural changes of bone could account for the lack of correlations between these 2 techniques at cortical sites.

Thyroid-stimulating hormone, thyroid hormones, and bone loss

It has become accepted by virtue of rich anecdotal experience and clinical research that thyrotoxicosis is associated with high-turnover osteoporosis. The bone loss, primarily due to accelerated resorption that is not compensated by a coupled increase in bone formation, has been attributed solely to elevated thyroid hormone levels. Evidence using mice lacking the thyroid hormone receptors alpha and beta establishes a role for thyroid hormones in regulating bone remodeling but does not exclude an independent action of thyroid-stimulating hormone (TSH), levels of which are low in hyperthyroid states, even when thyroid hormones are normal, as after thyroxine supplementation and in subclinical hyperthyroidism. We show that TSH directly suppresses bone remodeling and that TSH receptor null mice have profound bone loss, suggesting that reduced TSH signaling contributes to hyperthyroid osteoporosis. TSH and its receptor could become valuable drug targets in treating bone loss.

Bone: Does TSH concentration influence skeletal health?

Controversy surrounds the skeletal consequences of altered thyroid function. According to the latest report from the Tromsø population survey, however, variations of serum TSH concentration that remain within the normal range do not greatly influence BMD.

Osteoporosis and thyrotropin-suppressive therapy: reduced effectiveness of alendronate

BACKGROUND

Many reports of the effect of exogenous thyroxine therapy on bone mineral density (BMD) show a relationship between excess thyroid hormone administration and osteoporosis. The aim of this study was to evaluate the effect of antibone resorptive agents, in particular alendronate (ALN) on BMD in postmenopausal osteoporotic women with thyroid carcinoma who were receiving long-term thyrotropin (TSH)-suppressive therapy with thyroxine.

METHODS

Seventy-four postmenopausal women with low BMD (T-score < or =-2.5) and differentiated thyroid carcinoma on long-term TSH-suppressive therapy (TSH > or =0.05 and < or =0.1 microU/mL) for about 3-9 years were selected for the study. The patients were divided into three groups according to the length of levothyroxine (LT(4)) treatment prior to the beginning of the study: group A (TSH-suppressive therapy for about 3 years), group B (for about 6 years), and group C (for about 9 years). These patients were compared with 74 matched women not taking LT(4). All patients and controls were treated with bisphosphonates, calcium, and vitamin D for 2 years and evaluated.

RESULTS

After 24 months of treatment group A showed a 7.8% increase in lumbar BMD; group B, a 4.6% increase; and group C, a 0.86% increase. In the control group BMD increased 8.2%. A significant difference was found in both lumbar and femoral BMD increase among the three groups: group C had a lower BMD increase than group A (p < 0.001) and B (p < 0.001).

CONCLUSIONS

In postmenopausal women who were receiving adequate amounts of calcium and vitamin D in their diet ALN was less effective for those who were also receiving TSH-suppressive doses of LT(4) for either 6 or 9 years. The positive effect of ALN on BMD was less for longer periods of LT(4) treatment. It seems likely that other bisphosphonates would also be less effective in increasing BMD in postmenopausal women receiving TSH-suppressing doses of LT(4).