Management of subclinical hyperthyroidism

Hyperthyroidism induced by paraneoplastic human chorionic gonadotropin (hCG) production from testicular tumours: a retrospective clinical and histopathological study

Human chorionic gonadotropin (hCG) has structural similarities with thyroid-stimulating hormone (TSH) and may stimulate TSH receptors at higher concentrations. During pregnancy, placental hCG causes TSH suppression, contributing to hyperemesis. However, in males, clinical manifestations caused by excess hCG are rare. Herein, we describe complications of life-threatening thyroid storm caused by paraneoplastic hCG secretion from testicular germ cell tumours (GCTs) and aim to identify high-risk groups through retrospective analysis in n = 20 males (aged 17-55 years) with testicular hCG-positive GCTs. Seven hCG-positive testicular GCTs were classified as seminoma, and 13 were classified as non-seminomatous GCTs (NSGCTs). In 3/7 males with seminomas (43%), serum β-hCG concentrations were mildly elevated (median: 0.3 U/L; range: 0.3-82.1 U/L). In contrast, β-hCG was increased in 12/13 (92%) males with a NSGCT (median: 71.1 U/L; range: 0.3-1,600,000 U/L). In 10/13 males with NSGCT (77%), we detected components of embryonal cell carcinoma (EC), and in 7/13 (54%), we detected components of a choriocarcinoma (ChC). TSH was suppressed with high free thyroxine levels in two cases with NSGCT and excessively elevated β-hCG concentrations, but there was no TSH suppression in a further case with high β-hCG. One patient with NSGCT and high β-hCG levels presented with thyroid storm and imminent decompensation refractory to anti-thyroid treatment, requiring a total thyroidectomy. In the second patient, anti-thyroid treatment was initiated shortly after the diagnosis, successfully normalizing hyperthyroxinaemia. In conclusion, paraneoplastic β-hCG production, occurring in NSGCTs with components of ECs or ChCs, is a rare cause of thyrotoxicosis. Early recognition and treatment are critical to prevent a life-threatening thyroid storm.

Can Pre-Ablation Biomarkers Be Used to Predict Arrhythmia Recurrence after Ablation Index-Guided Atrial Fibrillation Ablation?

BACKGROUND

Ablation Index (AI) software has allowed better atrial fibrillation (AF) ablation results, but recurrence rates remain significant. Specific serum biomarkers have been associated with this recurrence.

OBJECTIVES

To evaluate whether certain biomarkers could be used (either individually or combined) to predict arrhythmia recurrence after AI-guided AF ablation.

METHODS

Prospective multicenter observational study of consecutive patients referred for AF ablation from January 2018 to March 2021. Hemoglobin, brain natriuretic peptide (BNP), C-reactive protein, high sensitivity cardiac troponin I, creatinine clearance, thyroid-stimulating hormone (TSH) and free thyroxine (FT4) were assessed for their ability to predict arrhythmia recurrence during follow-up. Statistical significance was accepted for p values of<0.05.

RESULTS

A total of 593 patients were included - 412 patients with paroxysmal AF and 181 with persistent AF. After a mean follow-up of 24±6 months, overall single-procedure freedom from atrial arrhythmia was 76.4%. Individually, all biomarkers had no or only modest predictive power for recurrence. However, a TSH value >1.8 μUI/mL (HR=1.82 [95% CI, 1.89-2.80], p=0.006) was an independent predictor of arrhythmia recurrence. When assessing TSH, FT4 and BNP values in combination, each additional "abnormal" biomarker value was associated with a lower freedom from arrhythmia recurrence (87.1 % for no biomarker vs. 83.5% for one vs. 75.1% for two vs. 43.3% for three biomarkers, p<0.001). Patients with three "abnormal" biomarkers had a threefold higher risk of AF recurrence compared with no "abnormal" biomarker (HR=2.88 [95% CI, 1.39-5.17], p=0.003).

CONCLUSIONS

When used in combination, abnormal TSH, FT4 and BNP values can be a useful tool for predicting arrhythmia recurrence after AI-guided AF ablation.

Factors predicting remission in hyperthyroid patients after low-dose I-131 therapy: 20 years retrospective study from a tertiary care hospital

OBJECTIVE

To assess the therapeutic outcome and factors predicting remission in hyperthyroid patients treated with low-dose I-131 (radioactive iodine) from a tertiary care hospital in South India.

METHODS

This 20-year single-institutional retrospective study was carried out on 3891 hyperthyroid adult patients. Only those patients with complete clinical records were audited. Selection criteria were based on patients with scintigraphic diagnosis of either Graves' disease (GD), toxic multinodular goitre (TMNG) or autonomous toxic nodule (ATN) and the records of those who received low-dose I-131 therapy (LDT) between March 2000 and 2020 at Amrita Institute, Cochin were analysed. SPSS 10 software was used for statistical analysis.

RESULTS

The records of 3891 hyperthyroid predominantly female patients were analysed. 65% patients had GD, 33% had TMNG and 3% were ATN. High rates of remission as early as 12 weeks (in 61% patients) was observed with a single dose of LDT while on strict iodine-free diet for 3-4 weeks prior to LDT. Study reveals that those with lower free T4 (fT4), small goitre (thyroid volume < 25 cm3), < 15% thyroid trapping function, shorter time duration from onset of hyperthyroidism to LDT, and treatment-naïve patients were factors determining high remission rates. Mann Whitney U test and Chi-square test was used to correlate variables in the remission and relapse groups. We found a positive correlation between fT4, thyroid volume (r = 0.35, p < 0.01) and trapping function (r = 0.34, p < 0.01), which were independent of age, sex, body mass index and TSH levels in our study.

CONCLUSION

High therapeutic outcome was observed with a single dose of LDT while on iodine-free diet. Remission with single dose of LDT occurred in 90% patients by 5th month. Of them 56% patients were treatment naive prior to LDT. LDT is thus a safe and effective therapy in hyperthyroid patients and can be recommended as a primary modality of management.

Changes in thyroid function and evolution of subclinical thyroid disease in older men

OBJECTIVE

Prevalence of subclinical thyroid disease increases with age, but optimal detection and surveillance strategies remain unclear particularly for older men. We aimed to assess thyroid stimulating hormone (TSH) and free thyroxine (FT4) concentrations and their longitudinal changes, to determine the prevalence and incidence of subclinical thyroid dysfunction in older men.

DESIGN, PARTICIPANTS AND MEASUREMENTS

Longitudinal study of 994 community-dwelling men aged ≥70 years without known or current thyroid disease, with TSH and FT4 concentrations assessed at baseline and follow-up (after 8.7 ± 0.9 years). Factors associated with incident subclinical thyroid dysfunction were examined by logistic regression and receiver operating characteristic analyses.

RESULTS

At baseline, 85 men (8.6%) had subclinical hypothyroidism and 10 (1.0%) subclinical hyperthyroidism. Among 899 men euthyroid at baseline (mean age 75.0 ± 3.0 years), 713 (79.3%) remained euthyroid, 180 (20.0%) developed subclinical/overt hypothyroidism, and 6 (0.7%) subclinical/overt hyperthyroidism. Change in TSH correlated with baseline TSH (r = .16, p < .05). Change in FT4 correlated inversely with baseline FT4 (r = -0.35, p < .05). Only higher age and baseline TSH predicted progression from euthyroid to subclinical/overt hypothyroidism (fully-adjusted odds ratio [OR] per year=1.09, 95% confidence interval [CI] = 1.02-1.17, p = .006; per 2.7-fold increase in TSH OR = 65.4, CI = 31.9-134, p < .001). Baseline TSH concentration ≥2.34 mIU/L had 76% sensitivity and 77% specificity for predicting development of subclinical/overt hypothyroidism.

CONCLUSIONS

In older men TSH concentration increased over time, while FT4 concentration showed little change. Subclinical or overt hypothyroidism evolved in one fifth of initially euthyroid men, age and higher baseline TSH predicted this outcome. Increased surveillance for thyroid dysfunction may be justified in older men, especially those with high-normal TSH.

The Power of the Heterogeneous Stock Rat Founder Strains in Modeling Metabolic Disease

Metabolic diseases are a host of complex conditions, including obesity, diabetes mellitus, and metabolic syndrome. Endocrine control systems (eg, adrenals, thyroid, gonads) are causally linked to metabolic health outcomes. N/NIH Heterogeneous Stock (HS) rats are a genetically heterogeneous outbred population developed for genetic studies of complex traits. Genetic mapping studies in adult HS rats identified loci associated with cardiometabolic risks, such as glucose intolerance, insulin resistance, and increased body mass index. This study determined underappreciated metabolic health traits and the associated endocrine glands within available substrains of the HS rat founders. We hypothesize that the genetic diversity of the HS rat founder strains causes a range of endocrine health conditions contributing to the diversity of cardiometabolic disease risks. ACI/EurMcwi, BN/NHsdMcwi, BUF/MnaMcwi, F344/StmMcwi, M520/NRrrcMcwi, and WKY/NCrl rats of both sexes were studied from birth until 13 weeks of age. Birth weight was recorded, body weight was measured weekly, metabolic characteristics were assessed, and blood and tissues were collected. Our data show wide variation in endocrine traits and metabolic health states in ACI, BN, BUF, F344, M520, and WKY rat strains. This is the first report to compare birth weight, resting metabolic rate, endocrine gland weight, hypothalamic-pituitary-thyroid axis hormones, and brown adipose tissue weight in these rat strains. Importantly, this work unveils new potential for the HS rat population to model early life adversity and adrenal and thyroid pathophysiology. The HS population likely inherited risk alleles for these strain-specific traits, making the HS rat a powerful model to investigate interventions on endocrine and metabolic health.

Mechanisms and Treatment Options for Hyperthyroid-Induced Osteoporosis: A Narrative Review

Normal thyroid hormone levels are crucial for the homeostasis of many metabolic cycles and processes throughout the human body. Thyroid dysfunction, such as thyrotoxicosis, can result from many different etiologies, including Graves' disease (GD), toxic multinodular goiter (MNG), and toxic adenoma. These hyperthyroid disease states can cause devastating complications and disease, including the disruption of the bone remodeling cycle and skeletal development, which can result in osteoporosis. Osteoporosis is characterized by a decrease in bone mineral density and a propensity for fragility fractures. In addition to patients with overt hyperthyroidism, studies have provided evidence of other high-risk patient demographics, such as individuals with subclinical hyperthyroidism and postmenopausal women, who may be at an increased risk for the development of secondary osteoporosis. The treatment of patients with hyperthyroid-induced osteoporosis often requires a multifaceted management plan that may be unique to each patient's situation. Antithyroid therapy is often the first step in treating this disease and may include thioamide medications. Radioactive iodine-131 therapy (RAI) and the surgical removal of the thyroid gland may also be reasonable approaches for restoring normal thyroid function. Following thyrotoxicosis mitigation, antiresorptive drugs such as bisphosphonates, calcitonin, and selective estrogen receptor modulators (SERMs) may be used to counteract decreased bone mineral density (BMD). Additionally, the implementation of vitamin D, calcium supplements, and weight-bearing exercise may also reduce bone loss. While the effects of thyroid stimulating hormone (TSH) and triiodothyronine (T3) on bone remodeling have been studied in the past, more research is needed to identify unknown mechanisms and develop future improved treatments for this condition.

Cardiovascular Outcomes of Differentiated Thyroid Cancer Patients on Long Term TSH Suppression: A Systematic Review and Meta-Analysis

We performed a systematic review and meta-analysis of the literature regarding cardiovascular outcomes of differentiated thyroid cancer (DTC) patients who are on long term thyroid stimulating hormone suppression. Searches were carried out using Prisma guidelines in Medline, Embase, CENTRAL, CINAHL and Scopus databases. Eligible papers were those which investigated discrete cardiovascular clinical outcomes in TSH suppressed patients and meta-analysis of selected studies was performed using Revman 5.4.1. We found a total of 195 879 DTC patients with median length to follow up of 8.6 years (range 5-18.8 years). Analysis showed DTC patients to be at higher risk of atrial fibrillation (HR 1.58, 95% CI 1.40, 1.77), stroke (HR 1.14, 95% CI 1.09, 1.20) and all-cause mortality (HR 2.04, 95% CI 1.02, 4.07). However, there was no difference in risk of heart failure, ischemic heart disease or cardiovascular mortality. These findings suggest that degree of TSH suppression must be titrated to accommodate risk of cancer recurrence and cardiovascular morbidity.

Thyroid function screening and follow-up of children with abdominal distension in Nanjing, China: a cross-sectional study

OBJECTIVE

To describe the thyroid function test among children with abdominal distention and to follow up the treatment received by children with abnormal thyroid function.

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

A total of 1089 children (median age:30 days (IQR=21-60 days) with abdominal distension were included in this single centre study in Nanjing, China.

RESULT

Thyroid dysfunction was found in 43 of 148 Hirschsprung's disease (HSCR) cases, with 3 (2.03%) having hypothyroidism, 3 (2.03%) having subclinical hypothyroidism and 3 (2.03%) having subclinical hyperthyroidism. Thyroid dysfunction was found in 206 of 941 functional abdominal distension cases, with 4 (0.43%) having hypothyroidism, 23 (2.4%) having subclinical hypothyroidism, 28 (2.9%) having subclinical hyperthyroidism and 1 (0.11%) having hyperthyroidism. Among total 65 cases (9 from HSCR, 56 from functional abdominal distension) diagnosed with thyroid diseases, 12 were treated with levothyroxine (LT-4), of which 9 were discontinued treatment at about 2 years old, and 3 were still receiving LT-4. Thirty-two cases received no treatment and thyroid function returned to normal in about 1 month. Twenty-one cases were lost during the follow-up.

CONCLUSION

The paediatrician should be vigilant for hypothyroidism when dealing with children with abdominal distension. Thyroid function should be followed up rather than simply administering a short-term levothyroxine treatment.

Subclinical hyperthyroidism in children

Subclinical hyperthyroidism (SH) is defined as serum thyroid-stimulating hormone (TSH) below the lower limit of the reference range in the presence of normal free T4 and free T3 levels. Depending on the degree of TSH suppression, SH could be defined as mild (TSH, 0.1-0.45 mU/L) or severe (TSH<0.1 mU/L). Patients with SH are often asymptomatic when symptoms are present, they are similar to the symptoms in patients with overt hyperthyroidism, although they are usually milder. The management of the SH is uncertain and should be individualized. We present this review after an extensive literature search and long-standing clinical experience. This review provides the prevalence, causes, clinical presentation, investigation, and therapeutic approach of SH in children.

Maternal subclinical hyperthyroidism and adverse pregnancy outcomes considering the iodine status: Tehran thyroid and pregnancy study

BACKGROUND

Unlike overt thyroid diseases, the impacts of subclinical thyroid dysfunction, especially subclinical hyperthyroidism (SH), on adverse pregnancy outcomes are inconclusive.

OBJECTIVE

We aimed to investigate the effect of maternal SH on adverse maternal and neonatal outcomes based on urinary iodine concentration (UIC).

METHODS

A secondary analysis was run on data collected in the Tehran Thyroid and Pregnancy study (TTPs). We used the data of 131 women with SH and 1650 cases of euthyroid. Serum levels of thyroid-stimulating hormone (TSH), thyroxine (T4), free thyroxine index (FT4I), and thyroid peroxidase antibody (TPOAb) were assessed at the first prenatal visit. A generalized linear regression model was applied to identify the effect of SH on the pregnancy outcomes based on UIC, and the effects were estimated with a 95% confidence interval.

RESULTS

Preterm delivery was observed in 12.3% of women with SH and 6.7% of those with euthyroid (P = 0.03). Women with TSH< 0.3 mIU/L had a higher odds of preterm delivery than those with TSH≥ 0.3 regardless of urine iodine cut-off [OR= 2.27; 95% CI: (1.15, 4.48), p = 0.02]. Among those with UIC levels≥ 150 μg/L, the odds ratio of preterm delivery was 4.61 folds higher in the SH group compared to those with euthyroid [95%CI: (1.36, 15.71), p = 0.01)]. No significant difference between these two study groups was found in Neonatal Intensive Care Unit admission. Moreover, the results revealed no statistically significant difference in the means of neonatal anthropometric parameters in the SH and euthyroid groups in none of the subgroups of UIC (<150 or ≥150 µg/l).

CONCLUSIONS

According to our results, maternal SH appears to be a risk factor for preterm delivery. This effect is more pronounced in women with higher UIC than those with lower UIC.

Clinical Parameters Are More Likely to Be Associated with Thyroid Hormone Levels than with Thyrotropin Levels: A Systematic Review and Meta-Analysis

Background: Though the functional states of other endocrine systems are not defined on the basis of levels of controlling hormones, the assessment of thyroid function is based on levels of the controlling hormone thyrotropin (TSH). We, therefore, addressed the question as to whether levels of thyroid hormones [free thyroxine (fT4), total triiodothyronine (TT3)/free triiodothyronine (fT3)], or TSH levels, within and beyond the reference ranges, provide the better guide to the range of clinical parameters associated with thyroid status. Methods: A PubMed/MEDLINE search of studies up to October 2019, examining associations of levels of thyroid hormones and TSH, taken simultaneously in the same individuals, with clinical parameters was performed. We analyzed atrial fibrillation, other cardiac parameters, osteoporosis and fracture, cancer, dementia, frailty, mortality, features of the metabolic syndrome, and pregnancy outcomes. Studies were assessed for quality by using a modified Newcastle-Ottawa score. Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed. A meta-analysis of the associations was performed to determine the relative likelihood of fT4, TT3/fT3, and TSH levels that are associated with the clinical parameters. Results: We identified 58 suitable articles and a total of 1880 associations. In general, clinical parameters were associated with thyroid hormone levels significantly more often than with TSH levels-the converse was not true for any of the clinical parameters. In the 1880 considered associations, fT4 levels were significantly associated with clinical parameters in 50% of analyses. The respective frequencies for TT3/fT3 and TSH levels were 53% and 23% (p < 0.0001 for both fT4 and TT3/fT3 vs. TSH). The fT4 and TT3/fT3 levels were comparably associated with clinical parameters (p = 0.71). More sophisticated statistical analyses, however, indicated that the associations with TT3/fT3 were not as robust as the associations with fT4. Conclusions: Thyroid hormones levels, and in particular fT4 levels, seem to have stronger associations with clinical parameters than do TSH levels. Associations of clinical parameters with TSH levels can be explained by the strong negative population correlation between thyroid hormones and TSH. Clinical and research components of thyroidology currently based on the measurement of the thyroid state by reference to TSH levels warrant reconsideration.

Type 2 Autoimmune Polyglandular Syndrome Presenting with Hyperpigmentation and Amenorrhea

A 36-year-old female presented with lethargy, anorexia, nausea, hyperpigmentation, weight loss and amenorrhea for six months. On examination, she had hyperpigmentation of face, hands and oral mucosa. Investigations revealed adrenal insufficiency and subclinical hyperthyroidism with elevated anti-thyroid peroxidase antibodies. Adrenal insufficiency in combination with Grave's disease and/or type 1 diabetes mellitus occurs in type 2 autoimmune polyglandular syndrome. It is a polygenic disorder occurring due to mutations in the human leukocyte antigen complex on chromosome 6. The patient was treated with oral hydrocortisone which led to improvement in all the symptoms.

The "slightly" abnormal thyroid test: What is the pediatrician to do?

Thyroid disorders are common in pediatrics. Tests of thyroid function are widely available and frequently ordered in the pediatric healthcare setting. This is sometimes driven by common signs or symptoms of thyroid disease. All too often, it is driven by patients and their parents requesting thyroid tests for nonspecific symptoms, such as fatigue, obesity or family history of thyroid disease. The decision to order thyroid tests, as well as which test(s) of thyroid function to order, deserves careful thought rather than a reflexive "thyroid panel" for every patient. Thyroid stimulating hormone (TSH) is the single most appropriate test of thyroid function when screening a pediatric or adolescent for thyroid disorders. Adding more tests only increases the likelihood that a minor (and often insignificant) abnormality will be found. These incidental abnormalities can create anxiety for the parent and child, and usually results in additional testing, referral to a pediatric endocrinologist, and further expense. This review will aim to guide the pediatric primary care provider on the choice of appropriate screening test(s) for acquired thyroid dysfunction in children and adolescents, as well as the proper interpretation of the test(s). Emphasis will be placed on the "slightly" abnormal thyroid screening test. Specific thyroid tests to be reviewed include TSH, (free) T4, (free) T3, and thyroid antibodies. Finally, this review will aim to guide decisions on follow-up, additional testing, and reasons for referral to a pediatric endocrinologist. Congenital hypothyroidism, including abnormalities on state newborn screening, will not be discussed.

Cardiothyreosis: Prevalence and risk factors

Cardiothyreosis (CT) or thyrotoxic heart disease is associated with higher morbidity and mortality than the other forms of hyperthyroidism. Its risk factors have been analyzed in a limited number of studies. The aims of our study were to investigate the prevalence of CT and its risk factors in patients with hyperthyroidism.

METHODS

We identified 538 patients with a hospital discharge diagnosis of hyperthyroidism from January 2000 to December 2015. Among them, 35 patients were diagnosed as having CT. Their demographic, clinical and biological characteristics were studied and compared with those of 72 controls (patients admitted for hyperthyroidism without CT) randomly selected using univariate and multivariate analysis.

RESULTS

The prevalence of CT in patients hospitalized with overt hyperthyroidism was 6.5%. The cardiac complications seen were atrial fibrillation (AF) in 33 cases (6.1%) and cardiac heart failure (CHF) in 11 cases (2%). The risk factors of CT were age greater than 50 years (OR=13.1; 95% CI [4.9-34.4]), low socioeconomic status (OR=2.8; 95% CI [1.2-6.7]), low educational level (OR=3.1; 95% CI [1.2-8.3]), personal history of hypertension (OR=3.5; 95% CI [1.1-11.2]) and a multinodular toxic goiter as the etiology of hyperthyroidism (OR=4.6; 95% CI [1.6-13.9]). After multivariate analysis, age greater than 50 years was the only independent risk factor of CT (adjusted OR=11.6; 95% CI [2.7-49.5]). Severe biological hyperthyroidism (FT4 >3 times normal) was associated with a lower risk of CT (adjusted OR=0.2; 95% CI [0.1-0.9]).

CONCLUSIONS

The prevalence of CT in patients with overt hyperthyroidism was relatively low. Cardiac complications were AF and CHF with a clear predominance of AF. Advanced age was the only independent risk factor of CT. Cardiac complications may be seen even if hyperthyroidism is not biologically severe.

Dementia and osteoporosis in a geriatric population: Is there a common link?

AIM

To determine the existence of a common pathological link between dementia and osteoporosis through reviewing the current evidence base.

METHODS

This paper reviews the current literature on osteoporosis and dementia in order to ascertain evidence of a common predisposing aetiology. A literature search of Ovid MED-LINE (1950 to June 2016) was conducted. The keywords “osteoporosis”, “osteoporotic fracture”, “dementia” and “Alzheimer’s disease” (AD) were used to determine the theoretical links with the most significant evidence base behind them. The key links were found to be vitamins D and K, calcium, thyroid disease, statins, alcohol and sex steroids. These subjects were then searched in combination with the previous terms and the resulting papers manually examined. Theoretical, in vitro and in vivo research were all used to inform this review which focuses on the most well developed theoretical common causes for dementia (predominantly Alzheimer’s type) and osteoporosis.

RESULTS

Dementia and osteoporosis are multifaceted disease processes with similar epidemiology and a marked increase in prevalence in elderly populations. The existence of a common link between the two has been suggested despite a lack of clear pathological overlap in our current understanding. Research to date has tended to be fragmented and relatively weak in nature with multiple confounding factors reflecting the difficulties of in vivo experimentation in the population of interest. Despite exploration of various possible mechanisms in search for a link between the two pathologies, this paper found that it is possible that these associations are coincidental due to the nature of the evidence available. One finding in this review is that prior investigation into common aetiologies has found raised amyloid beta peptide levels in osteoporotic bone tissue, with a hypothesis that amyloid beta disorders are systemic disorders resulting in differing tissue manifestations. However, our findings were that the most compelling evidence of a common yet independent aetiology lies in the APOE4 allele, which is a well-established risk for AD but also carries an independent association with fracture risk. The mechanism behind this is thought to be the reduced plasma vitamin K levels in individuals exhibiting the APOE4 allele which may be amplified by the nutritional deficiencies associated with dementia, which are known to include vitamins K and D. The vitamin theory postulates that malnutrition and reduced exposure to sunlight in patients with AD leads to vitamin deficiencies.

CONCLUSION

Robust evidence remains to be produced regarding potential links and regarding the exact aetiology of these diseases and remains relevant given the burden of dementia and osteoporosis in our ageing population. Future research into amyloid beta, APOE4 and vitamins K and D as the most promising aetiological links should be welcomed.

MECHANISMS IN ENDOCRINOLOGY: Impact of isolated TSH levels in and out of normal range on different tissues

Routine treatment of thyroid cancer (TC) includes long-term suppression of TSH. The necessity of this treatment in low- and intermediate-risk patients as well as the extent of TSH suppression is currently under discussion. A literature search was performed to illustrate the role of TSH in extrathyroidal cells and to identify potential reasons for different effects of exogenously suppressed and endogenously low TSH levels. Although adverse effects of subnormal and supranormal TSH blood levels on heart and brain have not been consistently found, studies show a clear negative effect of suppressed TSH levels on bone mineral density. Experimental data also support an important role of TSH in the immune system. The ability of levothyroxine (l-T4) to regulate TSH levels and triiodothyronine levels in a physiological manner is limited. Reduction of circadian changes in TSH levels, decrease of thyroid hormone-binding proteins, prevention of potential compensatory increases of TSH levels (e.g., in old age), and unresponsiveness of TSH-producing cells to TRH on l-T4 treatment might cause adverse effects of suppressed TSH levels. In view of the adverse effects of aggressive TSH suppression, achieving the suggested levels of TSH between 0.9 and 1 mU/l in the treatment of low-to-intermediate risk TC patients appears justified.

Impact of Free Thyroxine on the Outcomes of Left Atrial Ablation Procedures

The prevalence of atrial fibrillation (AF) is increased in hyperthyroidism. The degree to which thyroid hormones affect the outcomes of left atrial (LA) ablation is still unclear. From September 2010 to September 2013, 1,095 patients who underwent LA ablation (59.7% paroxysmal AF, 32.3% persistent AF, and 8.0% LA tachycardia) had their serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels measured in the 48 hours before the procedure. Patients were followed until they presented the first AF relapse after a blanking period of 3 months. TSH and FT4 were assessed as predictors of arrhythmia relapse and were adjusted for possible confounders. During a mean follow-up of 12.5 ± 7.9 months, 28.9% of patients presented an atrial arrhythmia relapse. TSH was not a predictor of relapse. In contrast, after adjustment, FT4 (median = 11.8 ng/L and interquartile range 10.6 to 14.6 ng/L) remained a predictor of relapse with 15% increase per quartile (hazard ratio 1.15, 95% confidence interval 1.03 to 1.29, p = 0.014). In conclusion, FT4 levels influence the success rate of LA ablation procedures, even when in the normal range.

Subclinical Thyroid Disorders: Clinical Significance and When to Treat?

Subclinical thyroid disorders are commonly encountered in the primary care setting. This article aims to review the latest evidence and guidelines pertaining to the management of subclinical hypo- and hyperthyroidism, in particular the important decision of when treatment should be considered.