Subclinical hyperthyroidism is not associated with progression of cardiac mass and development of left ventricular hypertrophy in middle-aged and older subjects: results from a 5-year follow-up

Subclinical Hyperthyroidism and Cardiovascular Disease

Background: In this narrative review, we assess published data on subclinical hyperthyroidism (SCHyper) and its association with cardiovascular disease (CVD) in the general population. Summary: We present data on the risk of SCHyper in relation to CVD outcomes, including atrial fibrillation (AF), heart failure, stroke, coronary heart disease (CHD), major adverse cardiac events (MACE), CVD mortality, and all-cause mortality. Evidence indicates that SCHyper is associated with an elevated risk of AF, heart failure, MACE, CVD mortality, and all-cause mortality. SCHyper appears to have little association with stroke risk and has shown conflicting results regarding CHD risk. Regarding the degree of serum TSH suppression, evidence shows a higher risk of CVD in SCHyper individuals with suppressed TSH (<0.1 mIU/L) compared with those with low TSH (0.1-0.4 mIU/L). Despite evidence that older individuals are inherently at a higher risk for CVD, no studies have yet demonstrated an age-related increase in the relative risk of CVD in SCHyper. Conclusion: The studies indicate that SCHyper is associated with an increased risk of AF, heart failure, MACE, CVD mortality, and all-cause mortality. Considering the importance of the degree of serum TSH suppression and age as risk factors for CVD, treatment decisions should be individualized based on their specific risk factors.

Four-dimensional speckle tracking echocardiography and fragmented QRS in detection of early left ventricular systolic dysfunction in patients with subclinical hyperthyroidism

BACKGROUND

Thyroid disorders are associated with many cardiovascular risk factors. The importance of thyroid hormones in the pathophysiology of heart failure is underlined by the European guidelines of the European Society of Cardiology. However, the role of subclinical hyperthyroidism (SCH) in subclinical left ventricular (LV) systolic dysfunction is not entirely clear.

METHODS

This cross-sectional study included 56 SCH patients and 40 healthy volunteers. The 56 SCH group was divided into two subgroups depending on the presence of fragmented QRS (fQRS). In both groups, left ventricular global area strain (LV-GAS), global radial strain (GRS), global longitudinal strain (GLS), and global circumferential strain (GCS) were obtained with four-dimensional (4D) echocardiography.

RESULTS

GAS, GRS, GLS, and GCS values were significantly different in SCH patients and in healthy volunteers. GLS and GAS values were lower in the fQRS+ than in the fQRS- group (-17.06 ± 1.00 vs. -19.08 ± 1.71, p < .001, and -26.61 ± 2.38 vs. -30.61 ± 2.57, p < .001, respectively). ProBNP was positively correlated with LV-GLS (r = 0.278, p = .006) and LV-GAS (r = 0.357, p < .001). Multiple linear regression analysis showed that fQRS was an independent predictor of LV-GAS.

CONCLUSIONS

4D strain echocardiography may be helpful for the prediction of early cardiac dysfunction in patients with SCH. The presence of fQRS may be an indicator of subclinical LV dysfunction in SCH.

Approach to the Patient With a Suppressed TSH

Subclinical hyperthyroidism (SCH) is a laboratory diagnosis defined by a serum thyrotropin (TSH) concentration below the reference range (< 0.4 mU/L in most assays), and a free thyroxine (FT4) and 3,5,3'-triiodothyronine levels (FT3) in the reference range. Many patients diagnosed with SCH will be clinically euthyroid while others may present with manifestations characteristic of thyroid hormone excess, such as tachycardia, tremor, intolerance to heat, bone density loss, or weight loss. In addition to the laboratory abnormalities, patient factors such as age, symptoms, and underlying heart and bone disease are used to stratify patients for the risk of adverse outcomes and determine the appropriate treatment. Evaluation should include repeat thyroid function tests to document persistent TSH suppression, investigation of the underlying cause, as well as evaluation of the patient's risk of adverse outcomes in the setting of a subnormal TSH. Persistent SCH has been associated with an increased risk of a range of adverse events, including cardiovascular events such as atrial fibrillation and heart failure, bone loss and fracture, and in some studies, cognitive decline. Despite the consistent association of these adverse events with SCH, prospective studies showing improved outcomes with treatment remain limited. Management options include observation without active therapy, radioactive iodine ablation of the thyroid, antithyroid medication, thyroid surgery, or radiofrequency ablation, as appropriate for the patient and clinical setting. The choice of therapy should be guided by the underlying etiology of disease, patient factors, and the risks and benefits of each treatment option.

Speckle tracking echocardiographic assessment of left ventricular longitudinal strain in female patients with subclinical hyperthyroidism

Background

Patients with subclinical hypothyroidism (SCH) are subjected to many cardiac changes. However, these changes are of gradual onset and cannot be usually detected using conventional diagnostic methods. Speckle tracking echocardiography (STE) is capable to detect cardiac function alterations usually unidentified by conventional echocardiography. The present study aimed to evaluate the role of STE in the detection of early cardiac changes in female patients with SCH.

Methods

The study included 33 female patients with SCH and 30 matched healthy volunteer women with normal thyroid functions who served as controls. Upon recruitment, all participants were subjected to careful history taking, thorough clinical examination and routine laboratory investigations, including thyroid-stimulating hormone and Free T4. The echocardiographic examination included conventional, color Doppler and two-dimensional STE.

Results

Analysis of conventional echocardiographic data revealed that patients had significantly higher end-systolic volume when compared with controls. In addition, it was noted that SCH patients had significantly lower mitral E/A ratio, isovolumetric relaxation time and significantly higher left atrium volume index in comparison to controls. In respect to STE data, we noted that patients had significantly lower values of mid-anteroseptal, apical lateral, apical septal, apical apex, AP4L strain and global strain % when compared with controls.

Conclusions

Patients with SCH have deteriorated global strain in comparison to healthy controls.

Thyroid hormones and modulation of diastolic function: a promising target for heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a clinical syndrome with high mortality for which there is no proven therapy to improve its prognosis. Thyroid dysfunction is common in heart failure (HF) and is associated with worse prognosis. In this review, we discuss the cardiovascular effects of thyroid hormones, the pathophysiology of HFpEF, the prognostic impact of thyroid function, and the potential of thyroid hormones for treatment of HFpEF. Thyroid hormones have a central role in cardiovascular homeostasis, improving cardiac function through genomic and non-genomic mechanisms. Both overt and subclinical hypothyroidism are associated with increased risk of HF. Even when plasmatic thyroid hormones levels are normal, patients with HF may have local cardiac hypothyroidism due to upregulation of type 3 iodothyronine deiodinase. Thyroid hormones improve several pathophysiological mechanisms of HFpEF, including diastolic dysfunction and extra-cardiac abnormalities. Supplementation with thyroid hormones (levothyroxine and/or liothyronine), modulation of deiodinase activity, and heart-specific thyroid receptor agonists are potential therapeutic approaches for the treatment of HFpEF. Further preclinical and clinical studies are needed to clarify the role of thyroid hormones in the treatment of HFpEF.

Graves' disease, multinodular goiter and subclinical hyperthyroidism

Subclinical hyperthyroidism is a common clinical entity, defined by serum TSH below the reference range, with normal FT4 and FT3 levels in an asymptomatic patient. Whether or not subclinical hyperthyroidism should be treated remains a matter of debate. Cross-sectional and longitudinal population-based studies demonstrate association of subclinical hyperthyroidism with risk of atrial fibrillation and osteoporosis, and with cardiovascular and all-cause mortality. However, there are no randomized clinical trials addressing whether long-term health outcomes are improved by treating subclinical hyperthyroidism; in the absence of evidence one way or the other, it seems appropriate to use decision trees taking account of TSH concentration and presence of risk factors (age>65 years or post-menopause, osteoporosis and cardiac disease).

Evaluation of ambulatory arterial stiffness index in hyperthyroidism

Background/aim: Hyperthyroidism causes hemodynamic changes that are associated with adverse cardiovascular outcomes. Twenty-four-hour ambulatory blood pressure monitoring recordings provide us with some essential data: BP variability and ambulatory arterial stiffness index (AASI). In this study, we aimed to investigate AASI and short-term BP variability in both overt and subclinical hyperthyroidism and their relationship with thyroid hormones. Materials and methods: We enrolled 36 patients with subclinical hyperthyroidism, 23 patients with overt hyperthyroidism, and 25 healthy euthyroid controls. ABPM recording was performed for 24 h for all patients. Results: There were no statistically significant differences among the overt hyperthyroidism, subclinical hyperthyroidism, and control groups in terms of AASI (0.43 ± 0.15, 0.38 ± 0.12, 0.42 ± 0.13, respectively; P = 0.315). Variability of diastolic BP was significantly higher in patients with overt hyperthyroidism than in patients with subclinical hyperthyroidism (14.8 ± 2.6 vs. 12.8 ± 2.5%, P = 0.023). There were significant positive correlations between AASI and fT3 (r = 0.246, P = 0.02) and fT4 (r = 0.219, P = 0.04) while TSH was not correlated with AASI (r = 0.023, P = 0.838). After adjusting for confounders, age, 24-h systolic and diastolic BP, variability of systolic and diastolic BP, and fT4 were independent predictors of AASI (r2 = 0.460, P < 0.001). Conclusion: Although AASI did not differ between overt and subclinical hyperthyroidism, there was a positive relationship between AASI and free thyroid hormone levels. Furthermore, short-term BP variability was higher in overt hyperthyroidism than in subclinical hyperthyroidism.

Childhood thyroid function, body composition and cardiovascular function

OBJECTIVE

The cardiovascular system is a known target for thyroid hormone. Early-life cardiovascular alterations may lead to a higher risk of cardiovascular disease in adulthood. Little is known about the effects of thyroid hormone on cardiovascular function during childhood, including the role of body composition in this association.

DESIGN

Population-based prospective cohort of children (n = 4251, median age 6 years, 95% range: 5.7-8.0 years).

METHODS

Thyroid-stimulating hormone (TSH) and free thyroxine (FT4) concentrations were measured to assess thyroid function. Left ventricular (LV) mass was assessed with echocardiography. Arterial stiffness was assessed with carotid-femoral pulse wave velocity (CFPWV). Systolic and diastolic blood pressure (BP) was measured. Body composition was assessed by dual-energy X-ray absorptiometry scan.

RESULTS

FT4 was inversely associated with LV mass (P = 0.002), and with lean body mass (P < 0.0001). The association of FT4 with LV mass was partially mediated through variability in lean body mass (55% mediated effect). TSH was inversely associated with LV mass (P = 0.010), predominantly in boys. TSH was positively associated with systolic and diastolic BP (both P < 0.001). FT4 was positively associated with CFPWV and diastolic BP (P < 0.0001, P = 0.008, respectively), and the latter association attenuated after adjustment for CFPWV.

CONCLUSIONS

At the age of 6 years, higher FT4 is associated with lower LV mass (partially through effects on lean body mass) and with higher arterial stiffness, which may lead to higher BP. Our data also suggest different mechanisms via which TSH and FT4 are associated with cardiovascular function during early childhood.

Thyroid hormones and cardiovascular disease

Myocardial and vascular endothelial tissues have receptors for thyroid hormones and are sensitive to changes in the concentrations of circulating thyroid hormones. The importance of thyroid hormones in maintaining cardiovascular homeostasis can be deduced from clinical and experimental data showing that even subtle changes in thyroid hormone concentrations - such as those observed in subclinical hypothyroidism or hyperthyroidism, and low triiodothyronine syndrome - adversely influence the cardiovascular system. Some potential mechanisms linking the two conditions are dyslipidaemia, endothelial dysfunction, blood pressure changes, and direct effects of thyroid hormones on the myocardium. Several interventional trials showed that treatment of subclinical thyroid diseases improves cardiovascular risk factors, which implies potential benefits for reducing cardiovascular events. Over the past 2 decades, accumulating evidence supports the association between abnormal thyroid function at the time of an acute myocardial infarction (MI) and subsequent adverse cardiovascular outcomes. Furthermore, experimental studies showed that thyroid hormones can have an important therapeutic role in reducing infarct size and improving myocardial function after acute MI. In this Review, we summarize the literature on thyroid function in cardiovascular diseases, both as a risk factor as well as in the setting of cardiovascular diseases such as heart failure or acute MI, and outline the effect of thyroid hormone replacement therapy for reducing the risk of cardiovascular disease.

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 hyperthyroidism impacts left ventricular deformation: 2D and 3D echocardiographic study

BACKGROUND

We sought to investigate left ventricular (LV) function and mechanics assessed by three-dimensional echocardiography (3DE) and speckle tracking in patients with subclinical hyperthyroidism (SCH).

METHODS

We included 35 untreated women with SCH and 35 healthy control women matched by age. All participants underwent laboratory analyses which included thyroid hormone levels, and complete 2DE and 3DE examination.

RESULTS

2DE LV longitudinal and circumferential strain was significantly decreased in the SCH subjects. 2DE LV systolic and early diastolic strain rates in longitudinal and circumferential directions were reduced, whereas late diastolic strain rates were increased in SCH individuals. 3DE LV end-diastolic volume and cardiac output were significantly elevated in the SCH patients. 3DE LV deformation in all three directions, as well as 3DE area strain, were significantly lower in the SCH group. Serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels correlated with 2DE LV mass index, 2DE longitudinal strain, and 3DE LV area strain in the whole study population.

CONCLUSION

LV deformation evaluated by 3DE and speckle tracking imaging are significantly impaired in SCH subjects. TSH and FT4 levels correlate with 2DE and 3DE LV structure and mechanics.

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.

Thyroid hormone levels within reference range are associated with heart rate, cardiac structure, and function in middle-aged men and women

BACKGROUND

Triiodothyronine (T3) has many effects on the heart, and marked changes in cardiac function and structure occur in patients with (subclinical) thyroid disease. We investigated whether between-subject variation in thyroid hormone levels within the euthyroid range is also associated with heart rate and echocardiographic heart function and structure.

METHODS

Subjects were selected from the Asklepios study (n=2524), a population-representative random sample of patients aged between 35 and 55 years, free from overt cardiovascular disease at baseline. Analyses were restricted to 2078 subjects (1013 women and 1065 men), not using antihypertensive or thyroid medication nor having antithyroperoxidase antibody levels above clinical cut-off or thyrotropin (TSH) levels outside the reference range. All subjects were phenotyped in-depth and underwent comprehensive echocardiography, including diastolic evaluation. Thyroid function parameters were determined by automated electrochemiluminescence.

RESULTS

Heart rate was robustly positively associated with (quartiles of) free T3 (FT3) and T3, both in subjects with TSH levels within reference (0.27-4.2 μU/L) and in narrow TSH range (0.5-2.5 μU/L; p<0.0001). FT3 and T3 were negatively associated with left ventricular (LV) end-diastolic volume but positively associated with relative wall thickness. Total T3 (TT3) was associated with enhanced ventricular contraction (as assessed by tissue Doppler imaging). Free thyroxine, FT3, and TT3 were positively associated with late ventricular filling, and TT3 was associated with early ventricular filling.

CONCLUSION

We have demonstrated a strong positive association between thyroid hormone levels within the euthyroid range and heart rate, and more subtle effects on cardiac function and structure. More specifically, we suggest a smaller LV cavity size (with increased relative wall thickness), an enhanced atrial and ventricular contraction, and LV relaxation with higher circulating thyroid hormones. These results illustrate that variation in thyroid hormone levels, even within the reference range, exerts effects on the heart.

Subclinical hyperthyroidism and the risk of cardiovascular events and all-cause mortality: an updated meta-analysis of cohort studies

OBJECTIVES

Whether subclinical hyperthyroidism (SCH) results in poor prognosis remains controversial. Our aim was to evaluate the association between SCH and the risk of cardiovascular disease (CVD), cardiovascular mortality, and all-cause mortality by conducting a meta-analysis of cohort studies.

METHODS

The PubMed and Embase databases were searched through November 2011 to identify studies that met pre-stated inclusion criteria. Relevant information for analysis was extracted. Either a fixed or a random effects model was used to calculate the overall combined risk estimates.

RESULTS

Seventeen cohort studies were included in this meta-analysis. The overall combined relative risks for individuals with SCH compared with the reference group were 1.19 (95% confidence interval (CI): 1.10 to 1.28) for CVD, 1.52 (95% CI: 1.08 to 2.13) for cardiovascular mortality, and 1.25 (95% CI: 1.00 to 1.55) for all-cause mortality. Subgroup analysis by sample source (community or convenience sample) showed that the significant association for cardiovascular and all-cause mortality only existed when pooling studies from convenience samples. Heterogeneity was observed when pooling studies on the association between SCH and cardiovascular and all-cause mortality. Sensitivity analysis showed omission of each individual study did not significantly change the pooled effects. No evidence of publication bias was observed.

CONCLUSIONS

Our findings demonstrated that SCH significantly increased the risk of CVD for the general population and the risk of cardiovascular and all-cause mortality for the individuals with other morbidities.

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.

The association between insulin-like growth factor-I and cardiac repolarization

OBJECTIVE

Previous studies reported associations between insulin-like growth factor I (IGF-I) serum concentration and cardiac morbidity and mortality, but the association between IGF-I serum concentration and cardiac repolarization has not been investigated in a population-based study so far. Therefore, we analyzed the impact of IGF-I concentrations on QTc, QT and RR intervals in two population based studies, The Study of Health in Pomerania (SHIP) and the Rotterdam Study.

DESIGN

457 individuals from SHIP and 155 individuals from the Rotterdam Study older than 55 years and without cardiovascular diseases and a left ventricular hypertrophy were investigated. IGF-I was determined by automated two-site chemiluminescence immunoassays and electrocardiograms were recorded by an ACTA electrocardiograph at a sampling frequency of 500 Hz. The association of IGF-I with QTc, QT and RR intervals was investigated by multivariable linear regression analyses adjusted for age, gender, diabetes mellitus, myocardial infarction, hypertension, body mass index, serum potassium and calcium in both studies separately and in pooled analysis.

RESULTS

There were no significant associations between log-transformed IGF-I and QTc interval in the single populations, whereas a significant inverse association was detectable in the pooled population (β, -15.6; 95%-confidence interval, -25.7, -5.5). The QTc interval was significantly higher in the first tertile of IGF-I compared to the third tertile (β, 5.4; 95%-confidence interval, 9.5-1.3) in the pooled analysis.

CONCLUSION

The inverse association between IGF-I serum concentrations and QTc interval in our study is suggestive of a higher risk for cardiac arrhythmias and thus might provide additional evidence for increased cardiovascular mortality in subjects with low IGF-I secretion.

Endogenous subclinical hyperthyroidism: who, when and why to treat

Subclinical hyperthyroidism is defined as serum thyroid hormone levels within their respective reference ranges in the presence of low-undetectable serum thyrotropin-stimulating hormone levels. Subclinical hyperthyroidism is associated with important cardiovascular risk factors and negative effects on bone metabolism and structure. However, there are conflicting results on cardiovascular mortality and the risk of bone fractures. Treatment and management of subclinical hyperthyroidism is controversial. This article will address the necessity to treat this disorder in relation to the cause of hyperthyroidism, the patient's age, the degree of thyroid-stimulating hormone suppression and the presence of comorbidities.

Should we treat mild subclinical/mild hyperthyroidism? No

The management of a patient with subclinical hyperthyroidism or mild thyroid over-activity is controversial. Subclinical hyperthyroidism is defined as a serum thyrotrophin (TSH) below the reference range but a normal thyroxine (T4) and triiodothyronine (T3) level in a patient who is either asymptomatic or has only non-specific symptoms. Epidemiological studies report an overall prevalence of approximately 3%, with men and women over 65 years and those in iodine deficient regions having the highest prevalence. Approximately 50% of subjects are taking levothyroxine. The aetiology for those with endogenous subclinical hyperthyroidism is Graves' disease, toxic nodular goitre or rarely a solitary toxic adenoma or thyroiditis. Non-thyroidal illness is an important cause of false positive low serum TSH test results. Subjects with low but detectable serum TSH values (0.1-0.4 mU/L) usually recover spontaneously when re-tested. It has been estimated that in those with an undetectable serum TSH (<0.1 mU/L) conversion to overt hyperthyroidism occurs at a rate up to 5% per year. Advocates of intervening for subclinical hyperthyroidism argue that early treatment might reduce mortality, prevent the later development of atrial fibrillation, osteoporotic fractures, and overt hyperthyroidism but data supporting improvement in outcomes are sparse. No appropriately powered prospective, randomised, controlled, double-blinded trial of intervention for subclinical hyperthyroidism exists. For the vast majority of patients adopting a "wait and see" policy rather than intervention may avoid unnecessary treatment or the potential for harm. Any potential benefits of therapy in subclinical hyperthyroidism must be weighed against the significant morbidity associated with the treatment of hyperthyroidism.

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).