Approach to the patient with subclinical hyperthyroidism

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.

Thyroid disorders in elderly: A comprehensive review

The approach to management of thyroid disorders in the elderly differs from that for younger individuals: it considers frailty of the population, coexisting medical illness and medications, clearance rate of medications and drug-drug interactions along with target organ sensitivity to the treatment. We present a comprehensive review of literature for the clinical presentation, pathophysiology, diagnostic evaluation, and management of thyroid disorders in the elderly.

Dose optimization of lithium to increase the uptake and retention of I-131 in rat thyroid

The present study was undertaken to optimize the dose of lithium, with an aim to increase the retention of I-131 in the thyroid follicles while maintaining the euthyroid state. 24 female Wistar rats weighing 110 ± 20 g were segregated into four groups. Animals in group I were fed standard laboratory feed and water throughout the period of experimentation. Animals in group II, III and IV were additionally fed with lithium in the form of lithium carbonate orally, at a dose of 10 mg/kg body weight, 20 mg/kg body weight, 30 mg/kg body weight respectively. The dose of lithium was started 1 week prior to radioiodine administration and continued thereafter for another 8 days. After 7 days of lithium treatment, 0.48 MBq of carrier-free I-131 was injected intraperitoneally into each rat, of the four groups. I-131 thyroidal uptake and biokinetics, as well as serum TSH, T3, T4 levels were estimated in all the treatment groups. A significant increase in the thyroid and whole body counts was observed after 4 and 24 h of I-131 aministration in lithium treated rats, compared to control animals. An increase in thyroidal effective t_1/2 and serum TSH levels, along with decrease in the levels of serum T3 and T4 was observed with a dose of 20 mg/kg or higher. In Conclusion, a Lithium dose of 10 mg/kg body weight in rats could increase the uptake of I-131 in the thyroid, without disturbing the control circulating levels of thyroid hormones.

Efficacy of Low-dose (2 millicurie) versus Standard-dose (4 millicurie) Radioiodine Treatment for Cats with Mild-to-Moderate Hyperthyroidism

Background

Radioiodine (¹³¹I) is effective treatment for hyperthyroidism in cats, but optimal dose to restore euthyroidism without inducing hypothyroidism is unclear. Treatment‐induced hypothyroidism can lead to azotemia and reduced duration of survival.

Objective

To compare efficacy and short‐term outcomes of low‐dose ¹³¹I versus higher, standard‐dose ¹³¹I as treatment for hyperthyroidism.

Animals

A total of 189 client‐owned cats undergoing ¹³¹I treatment for mild‐to‐moderate hyperthyroidism (serum T₄ ≥ 4.0 μg/dL and <13.0 μg/dL).

Methods

Prospective, nonrandomized, cohort study comparing treatment with either low‐dose (2 mCi, n = 150) or standard‐dose (4 mCi, n = 39) ¹³¹I. Serum T₄, thyroid‐stimulating hormone (TSH), and creatinine concentrations were measured after 1, 3, and 6 months to determine persistent hyperthyroidism, overt hypothyroidism (low T₄, high TSH), subclinical hypothyroidism (normal T₄, high TSH), and azotemia.

Results

There was no significant difference in prevalence of cats with persistent hyperthyroidism between standard‐ and low‐dose treatment groups at 3 (0% versus 5.3%; P = .34) and 6 (0% versus 3.3%; P = .51) months. Overt (18% versus 1%; P = .0005) or subclinical (46% versus 21%; P = .004) hypothyroidism was more common in cats at 6 months after standard‐dose ¹³¹I. No difference in incidence of azotemia existed between groups, but cats treated with standard‐dose ¹³¹I had higher creatinine concentrations (P < .05) and higher percent rises in creatinine (P < .0001).

Conclusions and Clinical Importance

Low‐dose ¹³¹I is safe and effective for cats with mild‐to‐moderate hyperthyroidism, as evidenced by a cure rate of >95% with reduced frequency of iatrogenic hypothyroidism and azotemia.

Early detection of biochemically occult autonomous thyroid nodules

OBJECTIVE

Autonomously functioning thyroid areas may be associated with subclinical or overt hyperthyroidism, but may exist even in the presence of normal TSH. This study was aimed at comparing the rate of autonomously functioning areas and their cardiac sequelae in patients with nodular goitre studied with the usual and a novel approach.

DESIGN AND METHODS

In total 490 adult outpatients with thyroid nodular goitre, living in a mild iodine-deficient area, were selected in our referral centre for thyroid diseases from 2009 to 2014 on the basis of a suspicion of thyroid functional autonomy. They were divided in three groups according to a non-conventional approach (excessive response to thyroxine treatment: group 1) or conventional approach (low/normal TSH with clinical suspicion or low TSH: groups 2 and 3). All patients of the study with the suspicion of thyroid functional autonomy underwent thyroid scan with radioactive iodine (I¹³¹) uptake (RAIU).

RESULTS

The percentage of confirmed thyroid functional autonomy was 319/490, being significantly higher in group 3 than in groups 1 and 2 (81.5 vs 64.7 vs 52.6%; chi-square P < 0.0001). However, the diagnosis with non-conventional approach was made at a significant earlier age (P < 0.0001). Cardiac arrhythmias as well as atrial fibrillation were similarly detected by conventional and non-conventional approaches (chi-square test: P = 0.2537; P = 0.8425).

CONCLUSIONS

The hyper-responsiveness to thyroxine treatment should induce the suspicion of thyroid functional autonomy at an early stage, allowing to detect autonomous functioning areas in apparently euthyroid patients.

The 2015 European Thyroid Association Guidelines on Diagnosis and Treatment of Endogenous Subclinical Hyperthyroidism

Endogenous subclinical hyperthyroidism (SHyper) is caused by Graves' disease, autonomously functioning thyroid nodules and multinodular goitre. Its diagnosis is based on a persistently subnormal serum thyroid-stimulating hormone (TSH) level with free thyroid hormone levels within their respective reference intervals. In 2014 the European Thyroid Association Executive Committee, given the controversies regarding the treatment of Endo SHyper, formed a task force to develop clinical practice guidelines based on the principles of evidence-based medicine. The task force recognized that recent meta-analyses, including those based on large prospective cohort studies, indicate that SHyper is associated with increased risk of coronary heart disease mortality, incident atrial fibrillation, heart failure, fractures and excess mortality in patients with serum TSH levels <0.1 mIU/l (grade 2 SHyper). Therefore, despite the absence of randomized prospective trials, there is evidence that treatment is indicated in patients older than 65 years with grade 2 SHyper to potentially avoid these serious cardiovascular events, fractures and the risk of progression to overt hyperthyroidism. Treatment could be considered in patients older than 65 years with TSH levels 0.1-0.39 mIU/l (grade 1 SHyper) because of their increased risk of atrial fibrillation, and might also be reasonable in younger (<65 years) symptomatic patients with grade 2 SHyper because of the risk of progression, especially in the presence of symptoms and/or underlying risk factors or co-morbidity. Finally, the task force concluded that there are no data to support treating SHyper in younger asymptomatic patients with grade 1 SHyper. These patients should be followed without treatment due to the low risk of progression to overt hyperthyroidism and the weaker evidence for adverse health outcomes.

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.

An update on subclinical hypothyroidism and subclinical hyperthyroidism

Subclinical thyroid dysfunction is characterized by normal levels of peripheral thyroid hormone, paired with a TSH level that is either lower than (subclinical hyperthyroidism) or higher than (subclinical hypothyroidism) the normal laboratory reference range. Slight shifts in peripheral hormone levels result in significant serum TSH changes. The exact upper limit of normal TSH and the management of subclinical hypothyroidism are still controversial. For those with TSH between high upper limit of normal and 10 mIU/L, the authors suggest selective use of thyroxine therapy. The authors agree with the general consensus in favor of therapy for those with serum TSH levels above 10 mIU/L. This recommendation is compatible with guidelines of American Thyroid Association and American Association of Clinical Endocrinologists. For subclinical hyperthyroidism persistent serum TSH <0.1 mIU/L should be treated particularly if the etiology is nodular toxic goiter. For serum TSH between 0.1 mIU/L and lower limit of normal, serum TSH co-morbidities such as cardiac risk factors and osteoporosis may favor therapy.

Differences in heart rate profile during exercise among subjects with subclinical thyroid disease

BACKGROUND

Clinical thyroid disease is associated with changes in the cardiovascular system, including changes in heart rate during exercise. However, data on the relation between subclinical thyroid disease (SCTD) and heart rate during exercise are limited.

METHODS

We investigated 3799 apparently healthy subjects who were evaluated in the Institute for Preventive Medicine at the Sheba Medical Center. All subjects answered standard health questionnaires; were examined by a physician; completed routine blood tests including thyrotropin, free triiodothyronine, and free thyroxine levels; and underwent a treadmill exercise according to the Bruce protocol. Subjects with known thyroid disease or those who were taking thyroid-related drugs were excluded from the analysis. Heart rate profile was compared between patients with subclinical hypothyroidism (SCHypoT), patients with normal thyroid function, and patients with subclinical hyperthyroidism (SCHyperT) using propensity score matching.

RESULTS

Seventy patients had SCHyperT and 273 had SCHypoT. Compared with age- and sex-matched normal subjects, SCHyperT subjects had a higher resting heart rate (83±17 vs. 76±12 beats per minute [bpm], p=0.006), a significantly higher recovery heart rate (94±12 vs. 90±12 bpm, p=0.045), and a significantly lower heart rate reserve (80±20 vs. 87±18 bpm, p=0.006). Subjects with SCHypoT showed a trend toward a lower resting heart rate (75±13 vs. 77±15 bpm, p=0.09) and had a significantly lower recovery heart rate (88±12 vs. 90±13 bpm, p=0.035). There was no significant difference in exercise duration or blood pressure between subjects with SCTD and their matched normal controls.

CONCLUSIONS

Subjects with SCTD have a significantly different heart rate profile during rest, exercise, and recovery.

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.

Higher free thyroxine levels are associated with frailty in older men: the Health In Men Study

OBJECTIVE

Frailty is common in the elderly and predisposes to ill-health. Some symptoms of frailty overlap those of thyroid dysfunction, but it is unclear whether differences in thyroid status influence risk of frailty. We evaluated associations between thyroid status and frailty in older men.

DESIGN

Cross-sectional epidemiological study.

PARTICIPANTS

Community-dwelling men aged 70-89 years.

MEASUREMENTS

Circulating thyrotropin (TSH) and free thyroxine (FT(4) ) were assayed. Frailty was assessed as ≥3 of the Fatigue, Resistance, Ambulation, Illnesses and Loss (FRAIL) scale's 5 domains: fatigue; resistance (difficulty climbing flight of stairs); ambulation (difficulty walking 100 m); illness (>5); or weight loss (>5%), blinded to hormone results.

RESULTS

Of 3943 men, 27 had subclinical hyperthyroidism, 431 subclinical hypothyroidism and 608 were classified as being frail (15·4%). There was an inverse log-linear association of TSH with FT(4). There was no association between TSH and frailty. After adjusting for covariates, men with FT(4) in the highest two quartiles had increased odds of being frail (Q3:Q1, odds ratio [OR] = 1·32, 95% confidence interval [CI] = 1·01-1·73 and Q4:Q1, OR = 1·36, 95% CI = 1·04-1·79, P = 0·010 for trend). Higher FT(4) was associated with fatigue (P = 0·038) and weight loss (P < 0·001). The association between FT(4) and frailty remained significant when the analysis was restricted to euthyroid men.

CONCLUSIONS

High-normal FT(4) level is an independent predictor of frailty among ageing men. This suggests that even within the euthyroid range, circulating thyroxine may contribute to reduced physical capability. Further studies are needed to clarify the utility of thyroid function testing and the feasibility of preventing or reversing frailty in older men.

Approach to and treatment of thyroid disorders in the elderly

Thyroid gland dysfunction is prevalent in older adults and may be associated with significant morbidity if misdiagnosed and left untreated. Because of a decreased number of symptoms at presentation, an increased susceptibility to adverse events if not treated, and a greater likelihood of harm from treatment, the diagnosis and management of thyroid disorders in older adults can be challenging. This review focuses on the epidemiology, clinical presentation, risks and complications, and management of thyroid disorders in older adults, including hyperthyroidism, hypothyroidism, thyroid nodules, and thyroid cancer.

Management of subclinical hyperthyroidism

The ideal approach for adequate management of subclinical hyperthyroidism (low levels of thyroid-stimulating hormone [TSH] and normal thyroid hormone level) is a matter of intense debate among endocrinologists. The prevalence of low serum TSH levels ranges between 0.5% in children and 15% in the elderly population. Mild subclinical hyperthyroidism is more common than severe subclinical hyperthyroidism. Transient suppression of TSH secretion may occur because of several reasons; thus, corroboration of results from different assessments is essential in such cases. During differential diagnosis of hyperthyroidism, pituitary or hypothalamic disease, euthyroid sick syndrome, and drug-mediated suppression of TSH must be ruled out. A low plasma TSH value is also typically seen in the first trimester of gestation. Factitial or iatrogenic TSH inhibition caused by excessive intake of levothyroxine should be excluded by checking the patient's medication history. If these nonthyroidal causes are ruled out during differential diagnosis, either transient or long-term endogenous thyroid hormone excess, usually caused by Graves' disease or nodular goiter, should be considered as the cause of low circulating TSH levels. We recommend the following 6-step process for the assessment and treatment of this common hormonal disorder: 1) confirmation, 2) evaluation of severity, 3) investigation of the cause, 4) assessment of potential complications, 5) evaluation of the necessity of treatment, and 6) if necessary, selection of the most appropriate treatment. In conclusion, management of subclinical hyperthyroidism merits careful monitoring through regular assessment of thyroid function. Treatment is mandatory in older patients (> 65 years) or in presence of comorbidities (such as osteoporosis and atrial fibrillation).

Thyroid disrupting chemicals in plastic additives and thyroid health

The globally escalating thyroid nodule incidence rates may be only partially ascribed to better diagnostics, allowing for the assessment of environmental risk factors on thyroid disease. Endocrine disruptors or thyroid-disrupting chemicals (TDC) like bisphenol A, phthalates, and polybrominated diphenyl ethers are widely used as plastic additives in consumer products. This comprehensive review studied the magnitude and uncertainty of TDC exposures and their effects on thyroid hormones for sensitive subpopulation groups like pregnant women, infants, and children. Our findings qualitatively suggest the mixed, significant (α = 0.05) TDC associations with natural thyroid hormones (positive or negative sign). Future studies should undertake systematic meta-analyses to elucidate pooled TDC effect estimates on thyroid health indicators and outcomes.

Thyroid Function Tests

A thyroid panel consisting of thyroid stimulating hormone (TSH) and free thyroxine (fT4) should form the first line of diagnostic tests; tri-iodothyronine (T3) — total or free may be needed occasionally. A TSH assay capable of detecting levels below 0.02mIU/L is required to differentiate the suppressed TSH levels typical in Graves' disease from subnormal levels seen in some geriatric patients, non-thyroidal illness, and patients on medications. Additional tests including thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), and TSH receptor antibody (TRAb) may be ordered to enable differential diagnosis when indicated. Serum thyroglobulin (Tg) may serve as a tumour marker for monitoring patients with differentiated thyroid cancer.

Effects of thyroid dysfunction on lipid profile

Thyroid dysfunction has a great impact on lipids as well as a number of other cardiovascular risk factors. Hypothyroidism is relatively common and is associated with an unfavorable effect on lipids. Substitution therapy is beneficial for patients with overt hypothyroidism, improving lipid profile. However, whether subclinical hypothyroidism should be treated or not is a matter of debate. On the other hand, hyperthyroidism can be associated with acquired hypocholesterolemia or unexplained improvement of lipid profile. Overall, thyroid dysfunction should be taken into account when evaluating and treating dyslipidemic patients.

Subclinical thyrotoxicosis in an outpatient population - predictors of outcome

OBJECTIVE

Individuals with endogenous subclinical thyrotoxicosis (SCT) may subsequently require treatment for overt disease. We aimed to evaluate the frequency of progression to hyperthyroidism and factors influencing this outcome.

DESIGN

This is a retrospective analysis of outcome in 96 consecutive patients (aged 16-91 years) diagnosed with SCT over a 6-year period. Individuals with secondary causes of TSH suppression were excluded. Mean follow-up was 3·8 years. The significance of age, gender, family history of thyrotoxicosis, symptoms at presentation, thyroid nodule(s) on clinical examination, entry TSH level, antithyroid antibody status and (99m) Tc pertechnetate thyroid imaging results on subsequent development of overt thyrotoxicosis was assessed.

RESULTS

Progression to overt thyrotoxicosis was seen in 8% at 1 year, 16% at 2 years, 21% at 3 years and 26% at 5 years. Multivariate analysis determined that diagnosis as determined by scintiscan to be the only independent predictor of outcome (P = 0·003) with the cumulative percentage requiring therapy at 5 years being 9% for subclinical Graves' disease, 21% for multinodular goitre and 61% for the autonomous nodule subgroup.

CONCLUSIONS

Progression of SCT to overt hyperthyroidism occurred at a rate of 5-8% per year with disease aetiology, as determined by thyroid scintigraphy, significantly influencing risk of progression.

Subclinical hypothyroidism and subclinical hyperthyroidism

Subclinical thyroid dysfunction occurs when peripheral thyroid hormone levels are within the normal laboratory reference range and the serum thyroid-stimulating hormone (TSH or thyrotropin) level is greater than normal (subclinical hypothyroidism) or less than normal (subclinical hyperthyroidism; TSH normal laboratory reference range: 0.3-5.0 mIU/l). For patients with subclinical hypothyroidism (serum TSH levels >10 mIU/l), thyroxine therapy is prescribed if other causes of TSH elevation and transient conditions have been excluded. For serum TSH levels between 5.0 and 10.0 mIU/l, selective therapy should be considered. For patients with sustained subclinical hyperthyroidism (serum TSH levels <0.1 mIU/l), therapy is recommended, especially in older patients. Observation or selective therapy should be considered for patients with serum TSH levels between 0.1 and 0.3 mIU/l.

Natural history of subclinical hyperthyroidism in elderly patients with TSH between 0.1 and 0.4 mIU/l: a prospective study

CONTEXT

One important aspect in the decision to treat or not elderly patients with subclinical hyperthyroidism (SCH) is the risk of progression to overt hyperthyroidism (OH).

OBJECTIVE

To define the natural history of endogenous SCH in elderly patients with TSH between 0.1 and 0.4 mIU/l.

DESIGN

Prospective study. One hundred and two women aged >or=60 years with persistently low TSH ranging from 0.1 to 0.4 mIU/l and normal free T4 and T3 were studied. Patients using L-T4 or antithyroid drugs, previously treated for hyperthyroidism, with pituitary disease, using corticosteroids, amiodarone, dopaminergic agonists, with atrial fibrillation or heart disease were excluded. Seven patients had Graves' disease, 91 had nodular disease and 4 presented no defined cause. The time of follow-up ranged from 12 to 70 months (median 41 months).

RESULTS

Three patients progressed to OH (elevated T4 and/or T3) and four other patients to persistently low TSH (<0.1 mIU/l) in the presence of increase in serum T3 when compared with baseline. These patients were treated. Twenty-four women presented sustained normalization of TSH and none progressed to hypothyroidism. SCH with TSH in the 0.1-0.4 mIU/l range persisted in 71 patients, 4 of them (5.6%) being treated because of the development of atrial fibrillation or heart disease during follow-up. The only independent predictor of progression of SCH was an initial TSH value <0.2 mIU/l.

CONCLUSIONS

In elderly patients with endogenous SCH and TSH between 0.1 and 0.4 mIU/l progression to clinical hyperthyroidism is uncommon (approximately 1% per year), spontaneous TSH normalization may occur, and persistence of SCH for many years is the most likely.

Acute myocardial infarction without significant coronary stenoses associated with endogenous subclinical hyperthyroidism

Subclinical hyperthyroidism is an increasingly recognized entity that is defined as a normal serum free thyroxine and free triiodothyronine levels with a thyroid-stimulating hormone level suppressed below the normal range and usually undetectable. It has been reported that subclinical hyperthyroidism is not associated with coronary heart disease or mortality from cardiovascular causes but it is sufficient to induce arrhythmias including atrial fibrillation and atrial flutter. Nowadays, there is growing interest regarding endogenous sublinical hyperthyroidism and the cardiovascular system. We present a case of acute myocardial infarction without significant coronary stenoses in a 75-year-old Italian woman with endogenous subclinical hyperthyroidism. Also this case focuses attention on the importance of a correct evaluation of endogenous subclinical hyperthyroidism.

Subclinical hyperthyroidism and sport eligibility: an exploratory study on cardiovascular pre-participation screening in subjects treated with levothyroxine for multinodular goiter

BACKGROUND

Subclinical hyperthyroidism (sHT) affects cardiovascular (CV) morphology and function; whether such changes can impact on sport eligibility is unclear.

AIM

This exploratory study evaluated the CV system and sport eligibility in athletes with levothyroxine-induced sHT, in the setting of mandatory pre-participation screening.

SUBJECTS AND METHODS

A full, non-invasive CV screening (history and physical examination, 12-lead ECG, echocardiography, 24-hour Holter ECG, exercise stress test) was performed in two groups of untrained female athletes affected by non-toxic multinodular goiter. One group was taking levothyroxine at mildly suppressive doses (TG) whereas the other was untreated (UG). There was also a group of healthy controls (HC).

RESULTS

In TG the following characteristics were observed: a) a higher resting heart rate (HR; p<0.01 and p<0.05, vs HC and UG respectively), b) a thicker left ventricular posterior wall (p<0.05 vs HC, and p<0.05 vs HC and UG, respectively), c) a higher mean HR during the 24-hour Holter ECG (p<0.01 and p<0.05, vs HC and UG respectively), and d) a lower achieved maximum work load (p<0.05, vs HC). No differences in the prevalence of cardiac arrhythmias among groups were observed. Sport eligibility was granted to all except one subject in the TG.

CONCLUSIONS

Although some alterations were found in athletes with levothyroxine-induced mild sHT, these are probably of limited clinical relevance and they did not contraindicate sport participation in the majority of cases. Future research to address both health risks and the need for specific evaluations (e.g. free thyroxine, TSH, echocardiography) during the preparticipation screening of athletes with sHT is warranted.

Thyroid cancer in young adults

The incidence of thyroid cancer in young adults is rising. Differentiated carcinoma (ie, papillary, follicular, and their variants) and medullary thyroid carcinoma (MTC) represent the two most common subtypes, with differing etiologies, prognoses, and management strategies. Ultrasound (US)-guided fine needle aspiration (FNA) is the best initial test for evaluating a nodule or mass suspicious for malignancy. Tumor histology, in addition to radiographic findings and clinical presentation, guides surgical management, the need for adjuvant therapies, and the optimal approach to long-term follow-up. Radioactive iodine (RAI) is used to reduce recurrence and improve survival for differentiated thyroid carcinomas (DTCs). Emerging systemic therapies provide options for patients with progressive metastatic MTC or radio-resistant DTC. Overall, the prognosis for the most common thyroid malignancy, papillary thyroid carcinoma (PTC), is excellent. The treatment of young adult thyroid cancer patients occurs optimally as part of a multidisciplinary coordination of care.

An analysis of the natural course of subclinical hyperthyroidism

BACKGROUND

Our aim was to evaluate the incidence rate of overt hyperthyroidism in a cohort of patients with subclinical hyperthyroidism and to assess the potential risk factors for the development of overt thyroid hyperfunction.

METHODS

We performed a retrospective analysis in 75 patients (68 women, mean age 62.2 +/- 14.2 years) with subclinical hyperthyroidism and different grades of serum thyrotropin (TSH) suppression. Incidence rate of overt hyperthyroidism and survival time, ie, time without requiring therapy for overt hyperthyroidism, were studied.

RESULTS

Thirty-four patients (45.3%) developed overt hyperthyroidism and 15 (20.0%) reverted to normal TSH values. The incidence rate of overt hyperthyroidism was 9.69 cases per 100 patient-year in the whole population and 4.12, 7.41, and 29.63 cases per 100 patient-year in subjects with initial TSH values of 0.30 to 0.49, 0.10 to 0.29, and <0.10 mU/L, respectively. Kaplan-Meier analysis of survival time curves showed that the development of overt thyroid hyperfunction was significantly related to the presence of symptoms of hyperthyroidism (P < 0.05) and low (<0.10 mU/L) TSH concentrations (P < 0.001). A stepwise multivariate Cox regression analysis showed that both symptoms and low TSH values were significant factors for progression to overt thyrotoxicosis.

CONCLUSIONS

TSH concentration is the most powerful predictor in the outcome of patients with subclinical hyperthyroidism. Our results suggest that patients with values under 0.10 mU/L have the highest probability to develop overt thyroid hyperfunction. In patients with TSH values higher than this value, the risk of progression is notably lower.

Subclinical hyperthyroidism: considerations in defining the lower limit of the thyrotropin reference interval

BACKGROUND

Although numerous reports have discussed the upper limit of the thyrotropin (TSH) reference interval, none have dealt with the lower limit. Recent recommendations regarding subclinical thyroid dysfunction give different advice about its management, depending on whether the TSH concentration is <0.1 mIU/L or 0.1-0.4 mIU/L.

CONTENT

We review key studies that have investigated the links between low TSH concentrations, cardiovascular morbidity, and mortality, with a focus on the TSH measurement threshold and assay type.

SUMMARY

Despite numerous consensus guidelines and publications of expert opinion, the management of subclinical hyperthyroidism remains largely intuitive and "nonevidence-based." The primary reason for this unsatisfactory situation is the absence of clinical-intervention trials. Important aspects that remain to be addressed are the influence of the method used to measure TSH, the definition of "normality," and the lack of evidence to base the grading of cardiovascular risk on the degree of TSH suppression. A risk-based approach should be adopted to determine the thresholds that would justify interventions. Such considerations assume, of course, that proof will emerge from ongoing clinical trials to support the medical utility of treating subclinical hyperthyroidism.

Bone and heart abnormalities of subclinical hyperthyroidism in women below the age of 65 years

The objective of the present study was to evaluate bone and cardiac abnormalities and symptoms and signs of thyroid hormone excess in women with subclinical hyperthyroidism (SCH) aged < 65 years. Forty-eight women with SCH were evaluated. The control group consisted of 48 euthyroid volunteers. The mean symptom rating scale score was significantly higher in patients. Cardiac involvement, both morphological and affecting systolic and diastolic functions, was also observed in patients. Women with SCH showed a significant increase in serum markers of bone formation and resorption. In addition, bone mineral density (BMD) was lower in the femoral neck but not in the lumbar spine in patients before menopause, whereas a lower BMD was observed at both sites in postmenopausal patients. SCH is not completely asymptomatic in women aged < 65 years, and is associated with heart abnormalities and with increased bone turnover and reduced BMD even before menopause.

The clinical significance of subclinical thyroid dysfunction

Subclinical thyroid disease (SCTD) is defined as serum free T(4) and free T(3) levels within their respective reference ranges in the presence of abnormal serum TSH levels. SCTD is being diagnosed more frequently in clinical practice in young and middle-aged people as well as in the elderly. However, the clinical significance of subclinical thyroid dysfunction is much debated. Subclinical hyper- and hypothyroidism can have repercussions on the cardiovascular system and bone, as well as on other organs and systems. However, the treatment and management of SCTD and population screening are controversial despite the potential risk of progression to overt disease, and there is no consensus on the thyroid hormone and thyrotropin cutoff values at which treatment should be contemplated. Opinions differ regarding tissue effects, symptoms, signs, and cardiovascular risk. Here, we critically review the data on the prevalence and progression of SCTD, its tissue effects, and its prognostic implications. We also examine the mechanisms underlying tissue alterations in SCTD and the effects of replacement therapy on progression and tissue parameters. Lastly, we address the issue of the need to treat slight thyroid hormone deficiency or excess in relation to the patient's age.

Thyroid disease and vascular function

Altered cardiac function in thyroid disease is well recognized and has been extensively investigated, vascular function has however been less well studied in those with thyroid dysfunction. Thyroid hormones, thyroxine (T(4)) and triiodothyronine (T(3)) are important regulators of cardiac function and cardiovascular hemodynamics. The cardiovascular system responds to minimal but persistent changes in circulating thyroid hormone levels producing changes in vascular reactivity and endothelial function. The detection of endothelial dysfunction and/or arterial stiffness allows early identification of individuals at risk as these occur in both patients with risk factors for coronary artery disease and in those with established disease. This may allow treatment to be targeted at high risk individuals with the aim of slowing the progression of vascular disease. The various methods used to assess arterial function are reviewed and the changes demonstrated in human and animal models of thyroid dysfunction.