The skeletal consequences of thyrotoxicosis

Resistance to thyroid hormone due to mutations in the THRB gene impairs bone mass and affects calcium and phosphorus homeostasis

CONTEXT

Resistance to thyroid hormone (RTH) is an inherited syndrome of reduced tissue responsiveness to thyroid hormone, which is usually due to mutations in the thyroid hormone receptor β gene (THRB). Few studies have been conducted to investigate bone and mineral metabolism in RTH.

OBJECTIVE

The objective of the study was to evaluate the clinical and biochemical parameters related to bone and mineral metabolism in RTH due to mutations in the THRB gene (RTHβ).

DESIGN AND PARTICIPANTS

We conducted a cross-sectional study on 14 patients with RTHβ (RTHG), eight adults and six children, and 24 control subjects (CG).

OUTCOMES

Serum measures included total calcium (TCa), inorganic phosphate (iP), alkaline phosphatase (AP), parathyroid hormone (PTH), 25-hydroxyvitamin D (25OHD), osteocalcin (OC), carboxyterminal telopeptide (CTX), and fibroblast growth factor 23 (FGF-23). We estimated the renal threshold phosphate concentration (TmPO4/GFR) and assessed bone mass using dual X-ray absorptiometry.

RESULTS

Adults and children with RTH showed higher serum levels of TCa than controls (P=.029 and, P=.018 respectively). However, only children with RTH exhibited lower serum levels of iP than controls (P=.048). FGF-23 was higher in RTHβ children (P=.04). RTHβ adults had lower whole-body (P=.01) and lumbar spine (P=.01) bone mineral density than control subjects. The same pattern was observed when the results were expressed as Z-scores between groups, with a lower value in RTHG than in CG for the lumbar spine of adults (P=.03). No difference was observed between groups in PTH, 25OHD, AP, OC, and CTX.

CONCLUSION

Biochemical abnormalities are seen in children with RTH (Low iP, high FGF23), while high calcium (with normal UCa) is seen in RTH subjects of all ages, and later on, in adult life, low BMD is seen. Considering that the TRα1 isoform is the predominant TR in the skeleton, we hypothesize that probably these patients may exhibit enhanced calcium flux from bone to circulation. Our data represent a challenge for new studies to unveil the control of calcium and phosphorus homeostasis and fracture risk in these patients.

Low serum thyrotropin level and duration of suppression as a predictor of major osteoporotic fractures-the OPENTHYRO register cohort

The relationship between thyrotoxicosis and osteoporotic fractures remains controversial, particularly in men. Register-based cohort study including all patients with a serum thyrotropin (TSH) measurement in the region of Funen 1996-2010. All TSH determinations were done in the same lab, which served all hospitals and General Practice (GP) practices in the region. Persons with raised TSH or a history of thyroid/pituitary disease or use of thyroid medications were excluded. The study population consisted of 222,138 (96%) persons with normal and 9217 (4%) with low TSH (<0.3 mIU/L). A single low TSH at baseline was associated with increased risk of hip fractures (adj HR 1.16, 95% CI 1.07-1.26, p < 0.001) but not major osteoporotic fractures (MOF, adj HR 1.06, 95% CI 0.99-1.12, p = 0.058) over a median follow-up of 7.5 years. When men were analyzed separately, results did not reach statistical significance. We found a significant association between duration of thyrotoxicosis and fracture. For each 6 months in which the mean TSH value was decreased (<0.3 mIU/L), hip fracture risk increased by a factor 1.07 (adj HR, 95% CI 1.04-1.10, p < 0.001) and MOF by 1.05 (adj HR, 95% CI 1.03-1.07, p < 0.001). Overt thyrotoxicosis was associated with an increased risk of hip fractures but not MOF. In euthyroid patients, the risk of fractures increased significantly with each SD unit of TSH decrease: Hip fracture (HR 1.45, 95% CI 1.22-1.71, p < 0.001) and MOF (HR 1.32, 95% CI 1.19-1.46, p < 0.001). In a population-based cohort, a single, first measurement of decreased TSH in patients without known thyroid disease was associated with an increased long-term risk of hip fracture, which remained significant in women but not in men after adjusting for confounders. Moreover, the risk of both hip fracture and MOF increased exponentially by the length of time during which TSH had remained low.

The multiple effects of thyroid disorders on bone and mineral metabolism

Differently from most hormones, which commonly are specialized molecules able to influence other cells, tissues and systems, thyroid hormones (TH) are pleiotropic peptides, whose primordial function is difficult to identify. The complex action of TH on human economy can be easily witnessed by examining the diverse consequences of TH excess and deficiency during development and after maturity. In particular, different manifestations in bone modeling and remodeling reflect the circumstantial consequences of thyroid disturbances, which are age dependent. While hyperthyroidism during childhood enhances bone mineralization and accelerates epiphyseal maturation, in adults it induces bone loss by predominant activation of osteoclast activity. Furthermore, the syndrome of TH resistance is a multifaceted condition in which different sites exhibit signs of hormone excess or deficiency depending on the configuration of the TH receptor isoform. The investigation of the impact of TH resistance on the skeleton still remains to be elucidated. We present here a thorough review of the action of TH on bone and of the impact of thyroid disorders, including hyper- and hypothyroidism and the syndrome of TH resistance, on the skeleton.

Management of Graves' disease: an overview and comparison of clinical practice guidelines with actual practice trends

Over the last century, much has been learned about the pathogenesis, manifestations, and management of Graves' disease leading to the establishment of evidence-based clinical practice guidelines. The joint clinical practice guidelines from the American Thyroid Association and the American Association of Clinical Endocrinologists give recommendations on both the diagnosis and treatment of hyperthyroidism. A survey of clinicians performed that same year, however, revealed that current practices diverge from these recently published guidelines in multiple areas. These differences will need to be assessed serially to determine the impact of the guidelines on future clinical practice and perhaps vice versa.

Exercise is associated with better quality of life in patients on TSH-suppressive therapy with levothyroxine for differentiated thyroid carcinoma

Objective : To evaluate if a supervised exercise training program improves the quality of life (QoL) of differentiated thyroid carcinoma (DTC) patients on TSH-suppressive therapy with levothyroxine (L-T4).Subjects and methods : Initially, a cross-sectional study was performed to compare the QoL and the health-related quality of life (HRQoL) between subclinical hyperthyroidism (SCH) patients (n = 33) and euthyroid subjects (EU; n = 49). In the prospective phase of the study, SCH patients were randomized in a non-blinded fashion to either participate (SCH-Tr = trained patients; n = 16) or not (SCH-Sed = untrained patients; n = 17) in a supervised exercise training program. The exercise program consisted of 60 minutes of aerobic and stretching exercises, twice a week, during twelve weeks. The QoL was assessed by the application of the WHOQOL-Bref, and the SF-36 was used to assess the HRQoL.Results : SCH patients had statistically lower scores than EU on the “physical” domain of WHOQOL-Bref, besides “physical function”, “role-physical”, “bodily pain”, “general health”, “vitality”, “role-emotional”, and “mental-health” domains of SF-36. After three months, SCH-Tr patients showed improvement in the “physical” and “psychological” domains of WHOQOL-Bref (p < 0.05), and in the “physical function”, “role-physical”, “bodily pain”, “vitality” and “mental health” domains of SF-36.Conclusion : Patients on TSH-suppressive therapy with L-T4 for DTC had impaired QoL and HRQoL compared to EU, but it was improved after 3-months of an exercise training program. Exercise seems to play an important role in the follow-up of DTC patients, since it seems to minimize the adverse effects of the treatment on QoL and HRQoL. Arq Bras Endocrinol Metab. 2014;58(3):274-81

Low bone mineral density is related to high physiological levels of free thyroxine in peri-menopausal women

OBJECTIVE

To determine whether thyroid hormone (free thyroxine (fT₄)) rather than TSH is directly related to bone mineral density (BMD).

DESIGN

Cross-sectional population cohort study of peri-menopausal women.

METHODS

Of a sample of 6846 peri-menopausal Dutch women who participated in an osteoporosis-screening programme, a cohort of 2584 was randomly selected for the assessment of thyroid function (TSH, fT₄ and thyroid peroxidase antibodies (TPO-Abs)). TPO-Ab-positive women, with a previous history of thyroid dysfunction, overt thyroid disease, subclinical hypothyroidism, osteoporosis or bilateral oophorectomy and those receiving thyroid hormone or hormone replacement therapy were excluded. Of 1477 eligible women, 1426 had TSH and fT₄ within the reference range and 51 had low or undetectable serum TSH. BMD was measured at the lumbar spine and low BMD was defined as <0.937 g/cm(2).

RESULTS

The mean BMD in the 51 women with low or undetectable serum TSH was 0.984 g/cm(2) compared with 1.001 g/cm(2) in the remaining 1426 (t=0.94, P=0.35); 33% of women with low or undetectable serum TSH had low BMD compared with 34% in 1426 euthyroid women. High fT₄ but not low TSH in euthyroid women was related to low BMD by multiple logistic regression corrected for age, BMI and smoking (OR, 1.30; 95% CI, 1.02-1.69).

CONCLUSIONS

Higher fT₄ levels within the normal reference range but not low or undetectable serum TSH were independently related to decreased BMD at lumbar spine in peri-menopausal women.

Identification of novel genetic Loci associated with thyroid peroxidase antibodies and clinical thyroid disease

Autoimmune thyroid diseases (AITD) are common, affecting 2-5% of the general population. Individuals with positive thyroid peroxidase antibodies (TPOAbs) have an increased risk of autoimmune hypothyroidism (Hashimoto's thyroiditis), as well as autoimmune hyperthyroidism (Graves' disease). As the possible causative genes of TPOAbs and AITD remain largely unknown, we performed GWAS meta-analyses in 18,297 individuals for TPOAb-positivity (1769 TPOAb-positives and 16,528 TPOAb-negatives) and in 12,353 individuals for TPOAb serum levels, with replication in 8,990 individuals. Significant associations (P<5×10(-8)) were detected at TPO-rs11675434, ATXN2-rs653178, and BACH2-rs10944479 for TPOAb-positivity, and at TPO-rs11675434, MAGI3-rs1230666, and KALRN-rs2010099 for TPOAb levels. Individual and combined effects (genetic risk scores) of these variants on (subclinical) hypo- and hyperthyroidism, goiter and thyroid cancer were studied. Individuals with a high genetic risk score had, besides an increased risk of TPOAb-positivity (OR: 2.18, 95% CI 1.68-2.81, P = 8.1×10(-8)), a higher risk of increased thyroid-stimulating hormone levels (OR: 1.51, 95% CI 1.26-1.82, P = 2.9×10(-6)), as well as a decreased risk of goiter (OR: 0.77, 95% CI 0.66-0.89, P = 6.5×10(-4)). The MAGI3 and BACH2 variants were associated with an increased risk of hyperthyroidism, which was replicated in an independent cohort of patients with Graves' disease (OR: 1.37, 95% CI 1.22-1.54, P = 1.2×10(-7) and OR: 1.25, 95% CI 1.12-1.39, P = 6.2×10(-5)). The MAGI3 variant was also associated with an increased risk of hypothyroidism (OR: 1.57, 95% CI 1.18-2.10, P = 1.9×10(-3)). This first GWAS meta-analysis for TPOAbs identified five newly associated loci, three of which were also associated with clinical thyroid disease. With these markers we identified a large subgroup in the general population with a substantially increased risk of TPOAbs. The results provide insight into why individuals with thyroid autoimmunity do or do not eventually develop thyroid disease, and these markers may therefore predict which TPOAb-positives are particularly at risk of developing clinical thyroid dysfunction.

Bone mineral density and bone turnover markers in patients on long-term suppressive levothyroxine therapy for differentiated thyroid cancer

Purpose

Current management for patients with differentiated thyroid cancer includes near total thyroidectomy and radioactive iodine therapy followed by administration of supraphysiological doses of levothyroxine (L-T4). Although hyperthyroidism is a well known risk factor for osteoporosis, the effects of L-T4 treatment on bone mineral density (BMD) in patients with thyroid cancer do not appear to be as significant as with endogenous hyperthyroidism. In this study, we evaluated the impact of long-term suppressive therapy with L-T4 on BMD and bone turn over markers in Korean female patients receiving L-T4 suppressive therapy.

Methods

We enrolled 94 female subjects (mean age, 50.84 ± 11.43 years) receiving L-T4 after total or near total thyroidectomy and radioactive iodine therapy for thyroid cancer (mean follow-up period, 12.17 ± 4.27 years). The subjects were divided into three groups by thyroid stimulating hormone (TSH) level (group 1 with TSH level ≤0.001 µIU/mL, group 2 with TSH level between 0.001 and 0.17 µIU/mL, group 3 with TSH level >0.17 µIU/mL) and four groups by quartile of free T4 level. L-T4 dosage, BMD (examined by dual-energy x-ray absorptiometry), and bone turnover markers were evaluated according to TSH and free T4 levels.

Results

No significant decrease was detected in BMD or bone turnover markers according to TSH level or free T4 level. Also, the prevalence of osteoporosis and osteopenia was not different among groups.

Conclusion

Long-term L-T4 suppressive therapy after thyroid cancer management did not affect bone density or increase the prevalence of osteoporosis even though TSH levels were supraphysiologically suppressed.

Treatment of Pathological Bone Fractures in a Patient with McCune-Albright Syndrome

McCune-Albright syndrome is a rare genetic disorder with typical skeletal and endocrine manifestations. The disease course is complicated by recurrent fractures resulting from polyostotic fibrous dysplasia and the treatment is thus primarily directed at the reduction of the risk of fractures. However, due to the complex mechanism of the skeletal damage the standard antiporotic therapeutics are ineffective. We report here a case of a 31-year-old female, diagnosed with the McCune-Albright syndrome in early childhood. She was suffering from extensive bone involvement, complicated by recurrent fractures despite the treatment with bisphosphonates. In addition, the disease course was complicated by the impairment of several endocrine functions—precocious puberty, hyperestrogenism, and hyperthyroidism for which a total thyroidectomy was performed. During the operation, two enlarged parathyroid glands were removed. This resulted in severe hypocalcaemia in the postoperative period with a need for supplementation with very high calcium and vitamin D doses. After this episode, the patient has remained free of fractures. We discuss here the corrected thyroid function, the supplementation with unconventionally high doses of vitamin D and calcium, and the termination of bisphosphonates treatment as presumable factors contributing to the reduced fracture risk in this patient.

Beyond the zebrafish: diverse fish species for modeling human disease

In recent years, zebrafish, and to a lesser extent medaka, have become widely used small animal models for human diseases. These organisms have convincingly demonstrated the usefulness of fish for improving our understanding of the molecular and cellular mechanisms leading to pathological conditions, and for the development of new diagnostic and therapeutic tools. Despite the usefulness of zebrafish and medaka in the investigation of a wide spectrum of traits, there is evidence to suggest that other fish species could be better suited for more targeted questions. With the emergence of new, improved sequencing technologies that enable genomic resources to be generated with increasing efficiency and speed, the potential of non-mainstream fish species as disease models can now be explored. A key feature of these fish species is that the pathological condition that they model is often related to specific evolutionary adaptations. By exploring these adaptations, new disease-causing and disease-modifier genes might be identified; thus, diverse fish species could be exploited to better understand the complexity of disease processes. In addition, non-mainstream fish models could allow us to study the impact of environmental factors, as well as genetic variation, on complex disease phenotypes. This Review will discuss the opportunities that such fish models offer for current and future biomedical research.

The clinical consequences of an ageing world and preventive strategies

Over the past century, the world has seen unprecedented declines in mortality rates, leading to an accelerated increase in the world population. This century will realise falling fertility rates alongside ageing populations. The 20th century was the century of population growth; the 21st century will be remembered as the century of ageing. Increase in life expectancy is one of the highest achievements of humankind; however, ageing and age-related disease is a mounting challenge for individuals, families, and for social, economic, and healthcare systems. Since healthy life expectancy has lagged behind the increase in life expectancy, the rise in morbidity will increase the burden on healthcare systems. Implementation of preventive health strategies to decrease, delay or prevent frailty, lung, breast and colon cancer, cardiovascular disease, metabolic syndrome, osteoporosis and osteopaenia, may increase health expectancy, and permit women to age gracefully and maintain independent living, without disability, for as long as possible.

The clinical utility of bone marker measurements in osteoporosis

Osteoporosis is characterised by low bone mass and structural deterioration of bone tissue, resulting in increased fragility and susceptibility to fracture. Osteoporotic fractures are a significant cause of morbidity and mortality. Direct medical costs from such fractures in the UK are currently estimated at over two billion pounds per year, resulting in a substantial healthcare burden that is expected to rise exponentially due to increasing life expectancy. Currently bone mineral density is the WHO standard for diagnosis of osteoporosis, but poor sensitivity means that potential fractures will be missed if it is used alone. During the past decade considerable progress has been made in the identification and characterisation of specific biomarkers to aid the management of metabolic bone disease. Technological developments have greatly enhanced assay performance producing reliable, rapid, non-invasive cost effective assays with improved sensitivity and specificity. We now have a greater understanding of the need to regulate pre-analytical sample collection to minimise the effects of biological variation. However, bone turnover markers (BTMs) still have limited clinical utility. It is not routinely recommended to use BTMs to select those at risk of fractures, but baseline measurements of resorption markers are useful before commencement of anti-resorptive treatment and can be checked 3–6 months later to monitor response and adherence to treatment. Similarly, formation markers can be used to monitor bone forming agents. BTMs may also be useful when monitoring patients during treatment holidays and aid in the decision as to when therapy should be recommenced. Recent recommendations by the Bone Marker Standards Working Group propose to standardise research and include a specific marker of bone resorption (CTX) and bone formation (P1NP) in all future studies. It is hoped that improved research in turn will lead to optimised markers for the clinical management of osteoporosis and other bone diseases.

How good is the levothyroxine replacement in primary hypothyroidism patients in Brazil? Data of a multicentre study

BACKGROUND

Studies from every continent have shown that only around 50% of the patients subjected to thyroid hormone replacement have TSH in the normal range. However, to date, there are no consistent data about Brazil.

OBJECTIVES

To evaluate levothyroxine (LT4) replacement treatment in patients with primary hypothyroidism followed in referral centers in Brazil.

METHODS

Patients with primary hypothyroidism followed in referral centers (University Hospitals from Universidade Federal do Rio de Janeiro - UFRJ, Unicamp, Universidade Federal do Paraná - UFPR and Universidade Federal do Ceará-UFC) answered a questionnaire that inquired about clinical and biochemical conditions, social- economic status, life quality and clinicians' orientations as well as their understanding about the information given. Serum TSH was checked close to the interview.

RESULTS

2292 consecutive patients met the inclusion criteria. Mean age 51.2 yr and TSH values between 0.4 and 4.0 mUI/l were considered to be within the reference range. Among all patients taking thyroid medication, 42.7% had an abnormal serum TSH (28.3% were undertreated and 14.4% were overtreated). Approximately all patients (99%) took LT4 in the morning but less than 30 min before breakfast (85.4%). Regarding the clinicians' orientations: 97.5% of the patients were instructed to take the medication daily, and 92.6% to take 30 min before breakfast (92.6%). However, only 52.1% were told not to take LT4 along with other medication.

CONCLUSIONS

Our study found that a significant number of patients taking thyroid hormones were not in the therapeutic range. Clinicians should, therefore, consider monitoring patients on thyroid replacement more frequently and being more precise on giving recommendations about the correct use of LT4.

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.