Hemostatic system as a risk factor for cardiovascular disease in women with subclinical hypothyroidism

Systematic review and meta-analysis of levothyroxine effect on blood pressure in patients with subclinical hypothyroidism

This study aims to evaluate the effect of levothyroxine therapy on blood pressure (BP) in patients with subclinical hypothyroidism (SCH). Were searched Six databases, and randomized controlled trials (RCT) and prospective cohort studies evaluating the effect of levothyroxine therapy on BP in patients with SCH were included. 37 articles (9 RCTs and 28 prospective cohorts) were included in this meta-analysis. Pooled analysis of RCT studies was insignificant; however, pooled analysis of 28 prospective cohort studies showed a significant difference before and after the therapy, reducing both systolic blood pressure (SBP) and diastolic blood pressure (DBP) (MD=-4.02 [-6.45, -4.58] and MD=-2.13 [-3.69, -0.56], both P-values<0.05). Levothyroxine therapy can play a role in lowering BP in patients with SCH. However, this effect is more observed in Caucasians, SCH patients with higher initial TSH followed by more remarkable TSH change to normal levels, and SCH patients with hypertension.

Cerebral Venous Thrombosis during Thyrotoxicosis: Case Report and Literature Update

Cerebral venous thrombosis (CVT) is a rare cause of stroke, particularly in young adults. Several known thrombophilic conditions may lead to an increased CVT risk. Interestingly, few cases in the literature have reported an association between CVT and thyrotoxicosis. Here, we describe the case of a young woman with CVT and concomitant thyrotoxicosis, without any other known prothrombotic conditions. We also performed a literature review of CVT cases and hyperthyroidism, searching for all articles published in peer-reviewed journals. We identified 39 case reports/case series concerning patients with CVT associated with thyrotoxicosis, highlighting, in most cases, the association with additional known prothrombotic factors. We then discussed the possible mechanisms by which hyperthyroidism could underlie a pro-coagulative state resulting in CVT. Thyroid disease might be a more common prothrombotic risk factor than expected in determining CVT. However, in most cases, a coexistence of multiple risk factors was observed, suggesting a multifactorial genesis of the disorder. We hope that this work may alert clinicians to consider thyrotoxicosis as a potential risk factor for CVT, even in patients who apparently have no other pro-coagulative conditions.

Relationship Between Subclinical Hypothyroidism and the Risk of Cardiovascular Complications

Subclinical hypothyroidism is characterized by raised thyroid-stimulating hormone levels in the presence of normal free thyroxine levels. When free thyroxine levels are normal and subclinical hypothyroidism is present, thyroid-stimulating hormone levels are elevated. The impact of subclinical hypothyroidism on the cardiovascular system has recently garnered attention because it is known that thyroid hormones impact the heart and its vasculature. There is compelling evidence linking subclinical hypothyroidism to increased cardiac risks, including changes in blood pressure and cholesterol. It is unclear whether subclinical hypothyroidism is associated with a higher risk of cardiovascular illnesses. In addition to discussing the advantages of levothyroxine therapy in delaying the onset of cardiovascular complications, this review makes the connection between subclinical hypothyroidism patients and the risk of cardiovascular complications-related death.

The Effect of Subclinical Hypothyroidism on Coagulation and fibrinolysis: A Systematic Review and Meta-Analysis

BACKGROUND

Despite patients with thyroid dysfunction show obvious abnormal hemostatic indicators in the peripheral blood, the current research on whether and how subclinical hypothyroidism (SCH) influence hemostatic function (the coagulation and fibrinolytic system) still remains controversial.

OBJECTIVE

We conducted this study to evaluate how SCH influence on the coagulation and fibrinolytic system in human body.

METHODS

Prior to March 2022, Web of Science, Embase, PubMed, WanFang, CNKI data and reference lists were searched to identify eligible researches. Two of us independently extracted the data and evaluated study quality. The effect size is represented by standard mean difference (SMD). Both fixed and random-effects models were used where appropriate. Review Manager 5.3 and STATA 16.0 were used to analyze the eligible data.

RESULTS

1325 patients from twelve observational studies were involved in our research. Our study revealed that SCH changed the heamostatic balance towards hypercoagulable and hypofibrinolytic conditions accompanied by an increase in tissue fibrinogen, plasminogen activator and plasminogen activator inhibitor-1. By contrast, there was no statistically difference in acivated partial thromboplastin time (APTT) and D-Dimer in SCH group compared with that in control subjects.

CONCLUSIONS

Our study confirmed that SCH is related with a prothrombotic state, as reflected by changes in both coagulation and fibrinolysis. It is highly recommended for screening cardiovascular risk factors in combination with an adequate evaluation of SCH state.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/prospero/#recordDetails] PROSPERO [CRD42021275313].

FMD and CIMT: Surrogate Markers of Atherosclerosis in Subclinical and Overt Hypothyroidism in Sub Himalyan Region

INTRODUCTION

Hypothyroidism increases the risk of atherosclerosis. Carotid intima-media thickness (CIMT) and flow-mediated dilation (FMD) have been used as a noninvasive method to detect atherosclerosis. But the literature is scarce on patients with subclinical hypothyroidism. Such a study was not done in our region, so we conducted this study at a tertiary care center to compare CIMT and FMD among subclinical and overt hypothyroid patients and to analyze the risk of atherosclerosis.

METHODS

We evaluated 68 patients aged 18-50 years, with newly diagnosed hypothyroidism. We divided them into overt and subclinical hypothyroidism groups and compared the findings. All analyses were performed by the computerized SPSS 17.0. The results were noted as means ± SD and percentage. Student's t-test was used to compare continuous variables, and the Chi-square test was used to compare differences.

RESULTS

The total number of patients with dyslipidemia in the subclinical hypothyroidism (SCH) group was 22 (45.83%) and in the overt hypothyroidism (OH) group was 26 (54.16%) with a P- value of 0.009. The mean FMD% in subclinical hypothyroidism patients was 6.9816 ± 3.4224 and in overt hypothyroidism patients was 5.3670 ± 2.7278 (P = 0.03). The mean CIMT was 0.5009 ± 0.0732, CIMT in the SCH group was 0.5082 ± 0.0672 and in the OH group was 0.5305 ± 0.0799 (P = 0.2).

CONCLUSION

The outcome of this study specifies that hypothyroidism is associated with endothelial dysfunction as established by impaired FMD, and it may be the first marker of atherosclerosis appearing before any structural evidence like CIMT. We can speculate that there is a link between subclinical hypothyroidism and atherosclerosis, and thyroxine replacement in SCH may help to prevent the progression of atherosclerosis.

Does Hypothyroidism Increase Complications, Lengths of Stay, Readmissions, and Costs Following Primary 1- to 2-Level Lumbar Fusion?

STUDY DESIGN

Level III-retrospective review.

OBJECTIVE

To evaluate the impact of hypothyroidism in patients undergoing 1- to 2-level lumbar fusion (1-2LF).

SUMMARY OF BACKGROUND DATA

Hypothyroidism is a common cause of morbidity and mortality following surgery. Studies have demonstrated the effects of hypothyroidism following orthopedic surgery, but not 1-2LF.

MATERIALS AND METHODS

Patients undergoing 1-2LF with hypothyroidism were identified within the Medicare population, and served as the study group. Study group patients were randomly matched to controls in a 1:5 ratio by age, sex, and medical comorbidities. Primary outcomes analyzed included in-hospital lengths of stay (LOS), 90-day readmission rates, 90-day medical complications, and costs of care. Pearson χ tests were used to compare patient demographics. Logistic regression analyses were used to calculate odds ratios (OR) for medical complications and readmissions. Welch t test was used to test for significance in cost between the cohorts. An α value <0.002 was considered statistically significant.

RESULTS

The query yielded 417,483 patients who underwent 1-2LF with (n=69,584) and without (n=347,899) hypothyroidism. Hypothyroid patients had significantly longer in-hospital LOS (8 vs. 4 d; P<0.0001) compared with controls. In addition, study group patients had significantly higher incidence and odds of 90-day readmissions (20.22% vs. 17.62%; OR, 1.18; P<0.0001) and 90-day medical complications (6.38% vs. 1.89%; OR, 3.53; P<0.0001) compared with controls. Study group patients had higher day of surgery costs ($97,304.01 vs. $95,168.35; P=0.014) and 90-day costs of care ($113,514.15 vs. $108,860.60; P=0.0001) compared with controls.

CONCLUSIONS

After adjusting for age, sex, and medical comorbidities, the study demonstrates patients who have hypothyroidism have longer in-hospital LOS and higher rates of readmissions, complications, and costs. The study is vital as it can allow orthopedic surgeons to adequately counsel and educate these patients of the potential complications that may occur following their procedure.

Parental history of coronary artery disease among adults with hypothyroidism: Case controlled study

Background

Thyroid dysfunction has a negative impact on coronary artery diseases (CAD) through several changes in its risk factors like dyslipidemia, glucose intolerance, and components of metabolic syndrome. Parental history of premature CAD may be an important risk factor for their offspring.

Objective

To investigate whether overt and subclinical hypothyroidism and the risk of atherosclerosis are present in adults with parental history of CAD.

Materials and methods

This case control study included 135 hypothyroid patients and 100 age-sex matched controls. Data were analyzed regarding CAD risk factors, hormonal and biochemical measures including retinol Binding Protein-4, fasting serum insulin, high-sensitivity C-reactive protein, lipid profile, fasting serum glucose, and serum malondialdehyde.

Results

Parental history of CAD was significantly higher in overt hypothyroidism than subclinical group (P = 0.001). The level of RBP-4 in hypothyroid patients was significantly higher than euthyroid subjects (P = 0.03), and was higher in hypothyroid patients with positive parental history of CAD (p = 0.01). There were positive relationships between RBP-4 and related cardiovascular risk factors and with hypothyroidism, its sensitivity and specificity were 47.9% and 42.5% respectively. The positive predictive value was 60.8% and the negative predictive value was 30.4%. Hypothyroid patients with parental history of CAD had a risk of 3.7 times more than the euthyroid subjects.

Conclusions

In hypothyroidism patients, parental history of CAD is a predictor of future coronary events and the related risk factors. RBP-4 is positively correlated with waist circumference, BMI, lipid profile, High-sensitivity CRP, MDA, fasting serum glucose, fasting serum insulin, HOMA indices and TSH.

Methylenetetrahydrofolate Reductase (MTHFR) C677T and A1298C Polymorphisms in Georgian Females with Hypothyroidism

The aim of this study was to investigate the frequency of methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms in Georgian females with hypothyroidism. Thirty-four patients and 29 healthy individuals were recruited in this study. Polymerase chain reaction-restriction fragment length polymorphism analyses were used for genotyping of MTHFR polymorphisms. The results of this study suggest that the MTHFR C677T variant was significantly associated with hypothyroidism. In addition, in individuals with T allele risk of hypothyroidism significantly increased. Combination of CT/AA genotypes was more prevalent in the hypothyroid patients than in the control group. Thus, C677T polymorphism could be a possible genetic factor contributing to the pathophysiology of hypothyroidism, possibly through hyperhomocysteinemia.

Thyroid Hormones and Cardiovascular Function and Diseases

Thyroid hormone (TH) receptors are present in the myocardium and vascular tissue, and minor alterations in TH concentration can affect cardiovascular (CV) physiology. The potential mechanisms that link CV disease with thyroid dysfunction are endothelial dysfunction, changes in blood pressure, myocardial systolic and diastolic dysfunction, and dyslipidemia. In addition, cardiac disease itself may lead to alterations in TH concentrations (notably, low triiodothyronine syndrome) that are associated with higher morbidity and mortality. Experimental data and small clinical trials have suggested a beneficial role of TH in ameliorating CV disease. The aim of this review is to provide clinicians dealing with CV conditions with an overview of the current knowledge of TH perturbations in CV disease.

Hypothyroidism increases 90-day postoperative complications in patients undergoing primary single level anterior cervical disectomy and fusion: a matched control analysis

Background

Anterior cervical discectomy and fusion (ACDF) is indicated for patients suffering from cervical radiculopathy, myelopathy, and degenerative disc disease, among other diseases. There is paucity in the literature regarding postoperative complications in patients undergoing primary ACDF with a diagnosis of hypothyroidism. The purpose of this study is to compare 90-day postoperative complications in patients with and without hypothyroidism undergoing primary ACDF.

Methods

A retrospective analysis was completed using a national administrative database known as Pearl Diver (Pearl Diver Technologies, Fort Wayne, Indiana) using the International Classification of Disease, ninth revision (ICD-9) codes. The study group consisted of patients having undergone ACDF with an active diagnosis of hypothyroidism 90 days prior to and on the day of surgery. Patients undergoing primary ACDF without hypothyroidism served as the control group. Patients in both groups were randomly matched according to age, gender, and Charlson-Comorbidity Index (CCI). The 90-day postoperative medical complications were assessed along with readmission rates and total cost of care.

Results

There were a total of 107,066 patients equally divided between the 2 cohorts. Patients with hypothyroidism had greater odds of developing complications such as non-healing surgical wound (OR: 2.27; P<0.001), pulmonary embolus (OR: 2.16; P<0.001), myocardial infarction (OR: 2.10; P<0.001), compared to patients in the control group after undergoing primary ACDF. Readmission rates were also higher in patients with hypothyroidism (OR: 1.45; P<0.001). Total cost of care was also greater in patients with hypothyroidism compared to patients without hypothyroidism undergoing primary ACDF.

Conclusions

Hypothyroidism is a risk factor for worse postoperative outcomes in patients undergoing primary ACDF. Appropriate preoperative optimization with thyroid hormone supplementation could potentially minimize the incidence of developing numerous medical complications, in addition to potentially lowering readmission rates and the total cost of care.

Study on Coagulation Factor VIII and Fibrinogen Levels in Patients with Thyroid Disorders

INTRODUCTION

A kaleidoscope of coagulation disorders has been reported in patients with thyroid dysfunctions. Globally, these disorders involve both primary and secondary hemostasis and range from subclinical laboratory abnormalities to, more rarely, life-threatening hemorrhages or thrombotic events. While overt hypothyroidism appears to be associated with a bleeding tendency, hyperthyroidism emerged to have an increased risk of thrombotic events. As a controversy, subclinical hypothyroidism and mild hypothyroidism have been reported as prothrombotic state. The mechanisms involved in these observations are also not conformed.

OBJECTIVE

To study the levels of prothrombotic coagulation factor VIII and fibrinogen in patients with thyroid disorder at baseline and to correlate the change in these factors after attaining euthyroid state by treatment.

STUDY DESIGN

This was a longitudinal interventional study.

SUBJECTS AND METHODS

Forty patients were recruited based on the inclusion and exclusion criteria, and their coagulation profile (prothrombin time, aPTT, Factor VIII, and fibrinogen levels), routine hematological, and biochemical profile was done at baseline and 6 weeks after attaining euthyroid state.

RESULTS AND CONCLUSION

Hyperthyroidism and mild hypothyroidism were found to be hypercoagulable states and moderate-to-severe hypothyroidism as hypocoagulable states. Nevertheless, further observational and intervention studies are needed to provide more definitive information on the clinical relevance of this association, along with the potential implication for prevention and treatment of coagulation/fibrinolytic abnormalities in patients with thyroid dysfunction.

Effect of Levothyroxine on Blood Pressure in Patients With Subclinical Hypothyroidism: A Systematic Review and Meta-Analysis

Background: Patients with subclinical hypothyroidism (SCH) have elevated blood pressure, but the effect of levothyroxine (LT4) therapy on blood pressure among those patients is still unclear. This study aimed to assess whether LT4 therapy could reduce blood pressure in SCH patients through a systematic review and meta-analysis. Methods: PubMed, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Science were searched. Randomized controlled trials (RCTs) assessing the effect of LT4 therapy on blood pressure or prospective follow-up studies comparing the blood pressure level before and after LT4 treatment were included, and the mean difference of systolic blood pressure (SBP) or diastolic blood pressure (DBP) was pooled using random-effect meta-analysis. Results: Twenty-nine studies including 10 RCTs and 19 prospective follow-up studies were eligible for the analysis. Meta-analysis of 10 RCTs suggested that LT4 therapy could significantly reduce SBP in SCH patients by 2.48 mmHg (95% CI -4.63 to -0.33, P = 0.024). No heterogeneity was observed among these 10 RCTs (I² = 0%). Meta-analysis of the 19 prospective follow-up studies found that LT4 therapy significantly decreased SBP and DBP by 4.80 mmHg (95%CI -6.50 to -3.09, P < 0.001) and 2.74 mmHg (95%CI -4.06 to -1.43, P < 0.001), respectively. Conclusion: The findings suggest that LT4 replacement therapy can reduce blood pressure in SCH patients, which needs to be validated in more clinical trials with larger samples.

Effect of Thyroxin Treatment on Carotid Intima-Media Thickness (CIMT) Reduction in Patients with Subclinical Hypothyroidism (SCH): a Meta-Analysis of Clinical Trials

Aim: Research shows that subclinical hypothyroidism (SCH) is related to an increased carotid intima –media thickness (CIMT), a surrogate marker of subclinical cardiovascular disease (CVD). It is controversial whether or not SCH should be treated to reduce CVD morbidity and mortality. This meta-analysis aimed to determine whether SCH is associated with an increase in CIMT as compared to Euthyroidism (EU) and whether thyroxin (T4) treatment in SCH can reverse the change in CIMT.

Methods: Two independent reviewers conducted an extensive database research up to December 2016. A total of 12 clinical trials discussed the effect of Thyroxin on CIMT values at pre- and post-treatment in subjects with SCH.

Results: CIMT was significantly higher among SCH (n = 280) as compared to EU controls (n = 263) at baseline; the pooled weighted mean difference (WMD) of CIMT was 0.44 mm [95% confidence interval (CI) 0.14, 0.74], p = 0.004; I² = 65%. After treatment with thyroxin in subjects with SCH (n = 314), there was a statistically significant decrease in CIMT from pre- to post-treatment; the pooled WMD of CIMT decrease was [WMD −0.32; 95% CI (−0.47, −0.16), p = < 0.0001; I² = 2%], and it was no longer different from EU controls [WMD 0.13 mm; 95% CI (−0.04, 0.30); p = 0.14; I² = 27%]. The total cholesterol (TC), triglycerides (TG), and low-density lipoprotein (LDL) were higher in SCH as compared to EU controls and decreased significantly after treatment with thyroxin.

Conclusion: This meta-analysis shows that thyroxin therapy in subjects with SCH significantly decreases CIMT and improves lipid profile, modifiable CVD risk factors. Thyroid hormone replacement in subjects with SCH may play a role in slowing down or preventing the progression of atherosclerosis.

The Effect of Early Substitution of Subclinical Hypothyroidism on Biochemical Blood Parameters and the Quality of Life

BACKGROUND

Subclinical hypothyroidism (SCH) is defined as high TSH and normal thyroxine. Data on the effects of early substitution by levothyroxine on psychophysical health in SCH are still not consistent enough to support its introduction.

METHODS

Clinical parameters, biochemical data and quality of life (Short Form 36 questionnaire) were measured before the intervention and 3 months after the euthyroid state had been achieved in SCH patients.

RESULTS

Significant reduction in body weight (p=0.030), systolic and diastolic blood pressure (p=0.024, p=0.019), homocysteine (p<0.001), leukocytes and neutrophils (p=0.011, p=0.001), INR (p=0.049), K levels (p=0.040, p=0.013), HbA1c (p=0.001), fasting insulin (p<0.001) and insulin resistance measured by HOMA index (p<0.001), lipid parameters (total cholesterol (p<0.001), LDL-cholesterol (p<0.001), triglycerides (p=0.007), apoB (p=0.022), Lp(a) (p<0.001), LDL/HDL (p=0.008), LAP (p=0.04) and apoB/apoA1 ratios (p<0.023)), TSH (p<0.001) and tAbs (p<0.001) was recorded. Frequency of fatty liver (20% to 2.9%, p=0.016), hyperlipidemia (85% to 65.7%, p=0.001) and metabolic syndrome (34.3% to 2.9%, p=0.070) significantly decreased. A statistically significant positive association was found between the average dose of levothyroxine and changes in physical functioning (r=0.391, p=0.020), vitality (r=0.393, p=0.020), mental health (r=0.374, p=0.027) and overall dimensions of mental health (r=0.376, p=0.026). With increasing doses of levothyroxine, the previously listed scores of SF 36 grew (r=0.296, p=0.084).

CONCLUSIONS

Early substitution of SCH improved the many clinical and biochemical parameters related to cardiovascular risk. Quality of life was also improved, and correlated only with thyroxine doses suggesting an indirect relationship between the degree of hypothyroidism and quality of life.

Hemostasis in Hypothyroidism and Autoimmune Thyroid Disorders

CONTEXT

There are contradictory results on the effect of hypothyroidism on the changes in hemostasis. Inadequate population-based studies limited their clinical implications, mainly on the risk of venous thromboembolism (VTE). This paper reviews the studies on laboratory and population-based findings regarding hemostatic changes and risk of VTE in hypothyroidism and autoimmune thyroid disorders.

EVIDENCE ACQUISITION

A comprehensive literature search was conducted employing MEDLINE database. The following words were used for the search: Hypothyroidism; thyroiditis, autoimmune; blood coagulation factors; blood coagulation tests; hemostasis, blood coagulation disorders; thyroid hormones; myxedema; venous thromboembolism; fibrinolysis, receptors thyroid hormone. The papers that were related to hypothyroidism and autoimmune thyroid disorder and hemostasis are used in this review.

RESULTS

Overt hypothyroidism is more associated with a hypocoagulable state. Decreased platelet count, aggregation and agglutination, von Willebrand factor antigen and activity, several coagulation factors such as factor VIII, IX, XI, VII, and plasminogen activator-1 are detected in overt hypothyrodism. Increased fibrinogen has been detected in subclinical hypothyroidism and autoimmune thyroid disease rendering a tendency towards a hypercoagulability state. Increased factor VII and its activity, and plasminogen activator inhibitor-1 are among several findings contributing to a prothrombotic state in subclinical hypothyroidism.

CONCLUSIONS

Overt hypothyroidism is associated with a hypocoagulable state and subclinical hypothyroidism and autoimmune thyroid disorders may induce a prothrombotic state. However, there are contradictory findings for the abovementioned thyroid disorders. Prospective studies on the risk of VTE in various levels of hypofunctioning of the thyroid and autoimmune thyroid disorders are warranted.

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 effects of pituitary and thyroid disorders on haemostasis: potential clinical implications

Disturbances of coagulation and fibrinolysis are usually multifactorial and growing evidence suggests that endocrinopathies modulate the haemostatic balance. The thrombotic alterations in endocrine disorders range from mild laboratory clotting abnormalities with little clinical significance to serious thrombotic and bleeding disorders directly related to hormonal disturbances. This literature review focuses on presenting the current data on the effects of thyroid and pituitary disorders on various parameters of the haemostatic system. With the exception of overt hypothyroidism which appears to cause a bleeding tendency, the rest of the endocrinopathies discussed in this review (subclinical hypothyroidism, hyperthyroidism, endogenous hypercortisolaemia, growth hormone deficiency, acromegaly, prolactinoma/hyperprolactinaemia and hypogonadotrophic hypogonadism) are associated with a hypercoagulable and hypofibrinolytic state, increasing the overall cardiovascular risk and thromboembolic potential in these patients. In most studies, the haemostatic abnormalities seen in endocrine disorders are usually reversible with successful treatment of the underlying condition and biochemical disease remission. High-quality studies on larger patient cohorts are needed to produce robust evidence on the effects of endocrine disorders and their therapeutic interventions on coagulation and fibrinolysis, as well as on the long-term mortality and morbidity outcomes in association with endocrine-related haemostatic imbalance. Given the rarity of some of the endocrine disorders, multicentre studies are required to achieve this target.

Association between thyroid dysfunction and venous thromboembolism in the elderly: a prospective cohort study

BACKGROUND

Venous thromboembolism (VTE) and subclinical thyroid dysfunction (SCTD) are both common in elderly patients. SCTD has been related to a hypercoagulable state and an increased thromboembolic risk. However, prospective data on the relationship between SCTD and VTE are lacking.

OBJECTIVES

To investigate the relationship between SCTD and recurrent VTE (rVTE), all-cause mortality, and thrombophilic biomarkers. Patients Elderly patients with VTE were studied.

METHODS

In a prospective multicenter cohort, thyroid hormones and thrombophilic biomarkers were measured 1 year after acute VTE, as both may be influenced by acute thrombosis. We defined subclinical hypothyroidism (SHypo) as elevated thyroid-stimulating hormone (TSH) levels (4.50-19.99 mIU L(-1) ), and subclinical hyperthyroidism (SHyper) as TSH levels of < 0.45 mIU L(-1) , both with normal free thyroxine levels. Outcomes were incidence of rVTE and overall mortality during follow-up starting after the 1-year blood sampling.

RESULTS

Of 561 participants (58% with anticoagulation), 6% had SHypo and 5% had SHyper. After 20.8 months of mean follow-up, 9% developed rVTE and 10% died. The rVTE incidence rate was 7.2 (95% confidence interval [CI] 2.7-19.2) per 100 patient-years in SHypo participants, 0.0 (95% CI 0.0-7.6) in SHyper participants, and 5.9 (95% CI 4.4-7.8) in euthyroid participants. In multivariate analyses, the sub-hazard ratio for rVTE was 0.00 (95% CI 0.00-0.58) in SHyper participants and 1.50 (95% CI 0.52-4.34) in SHypo participants as compared with euthyroid participants, without increased levels of thrombophilic biomarkers. SHyper (hazard ratio [HR] 0.80, 95% CI 0.23-2.81) and SHypo (HR 0.99, 95% CI 0.30-3.29) were not associated with mortality.

CONCLUSION

In elderly patients, SHyper may be associated with lower rVTE risks. SHypo showed a non-statistically significant pattern of an association with rVTE, without increased mortality or differences in thrombophilic biomarkers.

Subclinical Hypothyroidism and the Risk of Stroke Events and Fatal Stroke: An Individual Participant Data Analysis

OBJECTIVE

The objective was to determine the risk of stroke associated with subclinical hypothyroidism.

DATA SOURCES AND STUDY SELECTION

Published prospective cohort studies were identified through a systematic search through November 2013 without restrictions in several databases. Unpublished studies were identified through the Thyroid Studies Collaboration. We collected individual participant data on thyroid function and stroke outcome. Euthyroidism was defined as TSH levels of 0.45-4.49 mIU/L, and subclinical hypothyroidism was defined as TSH levels of 4.5-19.9 mIU/L with normal T4 levels.

DATA EXTRACTION AND SYNTHESIS

We collected individual participant data on 47 573 adults (3451 subclinical hypothyroidism) from 17 cohorts and followed up from 1972-2014 (489 192 person-years). Age- and sex-adjusted pooled hazard ratios (HRs) for participants with subclinical hypothyroidism compared to euthyroidism were 1.05 (95% confidence interval [CI], 0.91-1.21) for stroke events (combined fatal and nonfatal stroke) and 1.07 (95% CI, 0.80-1.42) for fatal stroke. Stratified by age, the HR for stroke events was 3.32 (95% CI, 1.25-8.80) for individuals aged 18-49 years. There was an increased risk of fatal stroke in the age groups 18-49 and 50-64 years, with a HR of 4.22 (95% CI, 1.08-16.55) and 2.86 (95% CI, 1.31-6.26), respectively (p trend 0.04). We found no increased risk for those 65-79 years old (HR, 1.00; 95% CI, 0.86-1.18) or ≥ 80 years old (HR, 1.31; 95% CI, 0.79-2.18). There was a pattern of increased risk of fatal stroke with higher TSH concentrations.

CONCLUSIONS

Although no overall effect of subclinical hypothyroidism on stroke could be demonstrated, an increased risk in subjects younger than 65 years and those with higher TSH concentrations was observed.

The Impact of Subclinical Hypothyroidism or Thyroid Autoimmunity on Coronary Vasospasm in Patients without Associated Cardiovascular Risk Factors

Background and Objectives

Subclinical hypothyroidism is associated with endothelial dysfunction and impaired coronary flow reserve. However, the effect of subclinical hypothyroidism or thyroid autoimmunity on variant angina has yet to be determined.

Subjects and Methods

Among 385 consecutive patients without associated cardiovascular risk factors who underwent coronary angiography with the ergonovine provocation test (EPT), 165 had a positive EPT {EPT(+)} and 220 had a negative EPT {EPT(-)}. The relationship between coronary artery spasm and the presence of subclinical thyroid dysfunction as well as serum thyroid peroxidase autoantibody (TPO Ab) was evaluated.

Results

The proportion of patients with subclinical hypothyroidism among those who were EPT(+) was significantly higher than that in those who were EPT(-) (18% vs. 11%, p=0.001). However, there was no significant difference in the proportion of patients with subclinical hyperthyroidism between the groups. Moreover, EPT(+) patients showed significantly more positive TPO Ab (33% vs. 14%, p<0.001) than those with EPT(-). There was a positive correlation between EPT(+) and TPO positivity (r=0.226, p<0.001), subclinical hypothyroidism (r=0.112, p=0.033), and body mass index (r=0.123, p=0.018). Binary logistic regression analysis revealed that the significant predictors of EPT(+) were body mass index {adjusted odds ratio (OR)=1.042, 95% confidence interval (CI)=1.005-1.080}, presence of subclinical hypothyroidism (OR=3.047, 95% CI=1.083-8.572), TPO Ab titer (OR=1.028, 95% CI=1.015-1.041), and the presence of TPO Ab (OR=4.904, 95% CI=1.544-15.567).

Conclusion

Subclinical hypothyroidism and the presence of TPO Ab are significantly associated with coronary vasospasm in patients without cardiovascular risk factors.

Thyroid disease and vascular risk

Subclinical hypothyroidism (SCH) is a common condition seen in up to 10% of adults, mainly women and the elderly. Several prospective longitudinal cohort studies have shown a higher risk of cardiovascular disease in people with SCH but mainly in younger individuals. There are also a number of interventional trials that have shown that treatment of SCH with levo-thyroxine improves cardiovascular risk factors, but there is a dearth of level 1 evidence regarding cardiovascular events. In addition, there is increasing proof concerning the association of abnormal thyroid function at the time of an acute myocardial infarction with adverse cardiovascular outcomes. This review describes the literature dealing with thyroid function in relation to cardiovascular disease and also outlines the effect of treatment in addressing cardiovascular risk.

Cardiovascular Risk in Patients with Subclinical Hypothyroidism

Subclinical hypothyroidism (SCH) has been associated with increased cardiovascular mortality due to adverse effects mainly on lipids and blood pressure (BP). There is evidence that SCH, especially in patients with thyroid-stimulating hormone (TSH) >10mU/l, may increase cardiovascular risk. Some uncertainty exists regarding the association of SCH with BP; however, that the coexistence of SCH with BP and hypercholesterolaemia has a negative cardiovascular impact is beyond doubt. Insulin resistance, by modulating various risk factors including coagulation, may potentially increase cardiovascular risk. Periodic health examinations including screening has been advised in patients >35 years of age, while treatment with thyroxine should be tailored to each patient.

Cerebral venous sinus thrombosis with autoimmune thyroiditis

Cerebral Venous Thrombosis (CVT) is a multifactorial condition which is described as idiopathic in 12.5% of patients. Hyperthyroidism has been associated with CVT in many case reports, and increased levels of factor VIII and von Willebrand factor (vWF) have been proposed as the possible link in this association, but only few rare case reports have described an association of hypothyroidism with CVT. We report here a case of autoimmune thyroiditis presenting with CVT.

Noninvasive indicators of atherosclerosis in subclinical hypothyroidism

INTRODUCTION

Cardiovascular system is rich in thyroid hormone receptors and is one of the major sites of action for thyroid hormones. However, the effect of subclinical hypothyroidism (SCH) on atherosclerosis has not been cleared yet.

MATERIALS AND METHODS

SCH is defined as high thyroid-stimulating hormone (TSH) levels in the presence of normal serum T4 and T3 levels. A total of 32 patients with SCH and 29 controls were included in the study. Carotid intima-media thickness, flow-mediated dilatation, and aortic distensibility were compared between the groups.

RESULTS

FMD was lower in patients with SCH than in controls. GTN-induced vasodilatation was similar in the patients with SCH and controls. There was no statistically significant difference between the patients with SCH and controls with respect to CIMT and aortic distensibility.

CONCLUSION

SCH is associated with endothelial dysfunction as established by FMD. Inconsistent results of CIMT and aortic stiffness can be explained by these parameters being measures of structural changes whereas FMD is a dynamic measure that reflects the impact of both acute and chronic influences on endothelial function.

Thyroid hormonal axis regulates protein C anticoagulation pathway in rats

Effects of the hormones of the hypothalamic-pituitary-thyroid axis on some basic parameters of the activity of protein C anticoagulation pathway in rats are studied. Thyrotropin-releasing hormone (0.06 mg/kg body mass), thyrotropin (1 IU/kg), triiodothyronine (T3) (0.08 mg/kg), thyroxine (T4) (0.08 mg/kg), administered subcutaneously for three consecutive days on four different groups of rats increased significantly activated protein C, free protein S and protein S activity, and reduced the soluble endothelial protein C receptor. Protein C antigen and total protein S were significantly elevated only by thyrotropin-releasing hormone and thyroid-stimulating hormone, but they were not affected by T3 and T4 treatment. The data indicate the hypothalamic-pituitary-thyroid axis is involved in the regulation of the protein C anticoagulation pathway in rats by activation of this system, suggesting a tendency of hypocoagulability.

Hypothyroidism and moderate subclinical hypothyroidism are associated with increased all-cause mortality independent of coronary heart disease risk factors: a PreCIS database study

BACKGROUND

Thyroid hormones have profound effect on the heart and peripheral vasculature. Hypothyroidism is associated with an increase in a number of coronary heart disease (CHD) risk factors including dyslipidemia, hypertension, and elevated levels of homocysteine. Our objective was to assess the effects of hypothyroidism (thyroid-stimulating hormone [TSH]: >10 μ U/mL), moderate subclinical hypothyroidism (SCH; TSH: 6.1-10 μ U/mL), and mild SCH (TSH: 3.1-6.0 μ U/mL) on cardiovascular risk factors, CHD prevalence, and all-cause mortality in patients at high risk for CHD seen in a preventive cardiology clinic.

METHODS

All patients seen in the Cleveland Clinic Preventive Cardiology clinic have demographic and laboratory tests including TSH and multiple CHD risk factors obtained at the baseline visit. All data are entered into a database (called PreCIS). The social security death index is queried monthly to determine all-cause mortality.

RESULTS

Several CHD risk factors including age, male gender, systolic blood pressure, triglycerides, and fibrinogen were more common in hypothyroid patients. Prevalence of CHD was more common in hypothyroid and moderate SCH patients. All-cause mortality was higher in hypothyroid and moderate SCH patients, but not in mild SCH patients. Higher mortality in these groups was observed in both genders, patients under 65 years of age, and patients not on thyroid replacement therapy, but was not observed in patients over 65 years of age.

CONCLUSIONS

Hypothyroidism and moderate, but not mild, SCH are associated with increased CHD prevalence and all-cause mortality. These observations suggest patients with moderate, but not mild, SCH and patients at high risk for CHD should be treated with thyroid replacement therapy.

Can subclinical hypothyroidism explain some sudden deaths due to pulmonary embolism without evident risk factors?

Thyroid pathology is rarely involved in the pathogenesis of sudden death in young people, and usually, when this is the case, is associated with acute changes of thyroid hormone blood levels. Three main thyroid causes of sudden death are known and used in tanathologic chains: thyrotoxicosis, myxedematous coma and, as of recently, lymphocytic thyroid infiltration. Coagulation disorders associated with thyroid disease are usually mild and not associated with sudden death. There are some studies showing an increased risk for unprovoked deep venous thrombosis in patients with hypothyroidism but there is none, to our knowledge, showing a correlation between hypothyroidism, deep venous thrombosis and sudden death. Our article suggests that subclinical hypothyroidism can lead to coagulation disorders and deep venous thrombosis which can explain some cases of sudden death associated with pulmonary embolism without other significant risk factors.

Subclinical hypothyroidism and the risk for cardiovascular diseases. Are epidemiological studies giving the right answers?

Vita tárgyát képezi, vajon a szubklinikus hypothyreosis káros hatást fejt-e ki a cardiovascularis rendszerre, amelynek a következménye megnövekedett morbiditás és mortalitás. Ennek a tisztázására számos epidemiológiai vizsgálatot végeztek, mégis ez idáig ezek nem adtak egyértelmű választ. A vizsgálatok kiértékelését számos zavaró körülmény befolyásolja, márpedig ezeket tekintetbe kell venni. A szerzők a TSH-vizsgálat végzésekor életkor-specifikus referenciatartomány meghatározását ajánlják, mivel az életkor előrehaladtával a TSH-szint magasabb érték felé tolódik el. Így elkerülhető lenne kissé emelkedett TSH-szintű idősebb betegek helytelen besorolása a szubklinikus hypothyreosisos csoportba. Újabb vizsgálatok arra utalnak, hogy szubklinikus hypothyreosisban a cardiovascularis betegség kockázata elsősorban a 65 életévnél fiatalabbakon növekszik meg. Ezt a lehetőséget is tekintetbe véve, a jövőben jól tervezett, prospektív, randomizált vizsgálatok elvégzése szükséges, amelyekben tekintetbe veszik a betegek életkorát, a vascularis eseményeket pedig elsődleges végpontnak tekintik. Remélhetőleg ezek megadják majd a választ arra a kérdésre is, vajon a tiroxinnal végzett korai szubsztitúciós kezelés megakadályozhatja-e ezen betegekben az ischaemiás szívbetegség kifejlődését. Orv. Hetil., 2010, 37, 1488–1494.

Thermogenic response and leptin levels rise after recovery of the euthyroid state

OBJECTIVE

The aims of the study were to compare: a) the thermogenic responses in subclinical hypothyroidism (SH) and euthyroid state; b) the relationship between thermogenic response and leptin level.

METHODS

Thirty women diagnosed with SH (mean age 39.9+/-4.1 yr; body mass index 23.2+/-2.5 kg/m(2)) were enrolled in the study. Thyroid function tests, leptin, and lipid profiles were measured during SH and after stable euthyroidism was recovered. Thermogenic response was measured by Water Immersion Calorimetry during SH and after the euthyroid state was attained.

RESULTS

The mean level of thermogenic response was found to be 1.45+/-0.43 kcal/kg*h in women with SH. It changed to 1.54+/-0.77 kcal/kg*h (p=0.01) in the euthyroid state; the change was statistically significant. Mean level of leptin was found to be 7.22+/-2.6 ng/ml in SH; and 15.8+/-8.0 ng/ml in the euthyroid state. There was a positive correlation between leptin and free T(3) (r=0.460, p=0.009) levels in SH. There were positive correlations between leptin level and fat mass in SH (r=0.820, p=0.01) and in the euthyroid state (r=0.700, p=0.03).

CONCLUSIONS

No correlations were found between thermogenic response and leptin levels in SH and in the euthyroid state. Thermogenic response and leptin levels rose after the euthyroid state was recovered.

Increasing levels of free thyroxine as a risk factor for a first venous thrombosis: a case-control study

A hypercoagulable state exists in hyperthyroidism, but the association with venous thrombosis (VT) is not fully explored. We aimed to investigate VT risk for different plasma levels of thyroid hormones and thyroid antibodies. We used a case-control study on leg vein thrombosis conducted between September 1999 and August 2006 at the Academic Medical Center, Amsterdam, The Netherlands. Parameters of thyroid function were assessed in 190 cases (mean age, 57 years; range, 19-90 years) and 379 sex-matched controls (mean age, 56 years; range, 18-93 years). Odds ratios (ORs) and 95% confidence intervals (CIs) for VT risk were estimated according to several cutoff levels derived from plasma levels observed in controls. We found the risk of VT to gradually rise with increasing levels of free thyroxine (FT(4)). In the absence of traditional acquired risk factors, FT(4) levels above 17 pmol/L yielded a sex- and age-adjusted OR of 2.2 (95% CI, 1.2-4.2) for deep VT, which further increased up to an OR of 13.0 (95% CI, 1.1-154.1) for FT(4) levels above reference range. Our data suggest increasing levels of FT(4) to be a risk factor for VT and may have implications for both the prevention and management of this disease.

Thrombin-Activatable Fibrinolysis Inhibitor (TAFI) Antigen and Activity Assay in Patients With Primary Hypothyroidism

Hypothyroidism causes a tendency for cardiovascular diseases. It was recently shown that thrombin-activatable fibrinolysis inhibitor (TAFI) attenuates fibrinolysis and also fibrin-plasminogen interaction by the removal of lysine and arginine residues from fibrin monomers. The aim of this study was to determine the effects of overt hypothyroidism on the levels of TAFI antigen (TAFI Ag) and TAFI activity (TAFIa). Thirty-one overt primary hypothyroid patients and age- and gender-matched 25 healthy controls were enrolled in the study. Patients were treated with L-thyroxine after the collection of blood samples. Thyroid functions were reevaluated following the achievement of euthyroid status. Thrombin-activatable fibrinolysis inhibitor Ag, tissue plasminogen activator (t-PA), and plasminogen activator inhibitor 1 (PAI-1) levels were measured with the enzyme-linked immunosorbent assay (ELISA). Thrombin-activatable fibrinolysis inhibitor activity was assessed with the chromogenic assay. Thrombin-activatable fibrinolysis inhibitor Ag (1.63% ± 0.42% vs 1.32% ± 0.36%, P < .01) and TAFIa (14.2 ± 4.12 vs 11.6 ± 3.49 μg/mL, P < .05) levels were elevated in hypothyroid patient compared to controls. Plasminogen activator inhibitor 1 and t-PA levels were not significantly different between both groups. In hypothyroid patients, TAFI Ag levels were correlated with free T4 (r = -.373, P < .05) and thyroid-stimulating hormone (TSH) levels (r = .748, P < .001). Regression analysis showed that TSH levels were predictors of TAFI Ag levels (P < .001, β =.671, 95% confidence interval [CI]: 0.008-0.017). Following L-thyroxine treatment, TAFI Ag (1.63% ± 0.42%, 1.34% ± 0.33%, P < .05) and TAFIa (14.2 ± 4.12 μg/mL, 12.0 ± 2.77 μg/mL, P < .05) levels were significantly decreased, but t-PA and PAI-1 levels remained unchanged. This results point out that the fibrinolytic activity was decreased in hypothyroid patients, and therefore the achievement of euthyroid status is important in ameliorating the increased risk of cardiovascular disease.

Coagulation and fibrinolysis in thyroid dysfunction

Various abnormalities of hemostasis, ranging from subclinical laboratory abnormalities to clinically significant disorders of hemostasis, and rarely major hemorrhage or thromboembolism, may occur in patients with thyroid diseases. The objective of this review is to discuss the relationships between thyroid dysfunction and hemostasis (primary hemostasis and coagulation/fibrinolytic system). According to the recent literature, most of the hemostatic abnormalities associated with thyroid dysfunction are the consequences of direct effects of thyroid hormones on the synthesis of various hemostatic parameters. Thyroid autoimmunity may also modify the processes of primary and secondary hemostasis. We have concluded that hyperthyroidism is generally associated with hypercoagulability and hypofibrinolysis, whereas the hemostatic profile in hypothyroidism depends on the severity of the disease. As few data are available on hemostasis in subclinical thyroid disease, further studies on this subject are needed.

Thyrotropin levels and their relationship with cardiovascular risk factors in the island of Gran Canaria, Spain. Implications of lowering the upper reference limit of thyrotropin stimulating hormone

OBJECTIVE

To characterize the cardiovascular risk profile of subjects with high and normal-high concentrations of serum TSH in a sample of adult Spanish subjects from the island of Gran Canaria.

DESIGN

Cross-sectional population-based study.

SUBJECTS

After excluding 28 individuals on current treatment with levothyroxine and 9 others with TSH levels below the range of normality (0.3-4.9 mU/l), 704 randomly selected subjects (412 women; age range: 30-82 yr) belonging to the Telde Study were assessed.

MEASUREMENTS

Participants underwent physical examination and fasting blood analyses to determinate TSH, serum lipids, homocysteine, fibrinogen, von Willebrand factor, plasminogen activator inhibitor- 1, C-reactive protein, and insulin.

RESULTS

Twenty-nine participants had serum TSH concentrations above the normal range of normality. Among all the studied variables, only female sex and diastolic blood pressure were significantly associated with TSH levels > or =5 mU/l in a multivariate logistic regression analysis. If the upper normal limit of TSH was reduced up to 2.4 mU/l, an additional group of 106 subjects would be considered to have elevated TSH levels. A serum TSH > or =2.5 mU/l was positive and independently associated with female sex, body mass index, total cholesterol, and homocysteine, and negatively associated with smoking.

CONCLUSIONS

Although the impact of serum TSH levels on cardiovascular risk cannot be established from these findings, TSH values within the upper part of the usually accepted normal range were demonstrated to be associated with well-recognized risk factors for cardiovascular disease.

Metabolic and cardiovascular risk in patients with a history of differentiated thyroid carcinoma: A case-controlled cohort study

Hyperthyroidism seems to increase metabolic and cardiovascular risk, while the effects of sub-clinical hyperthyroidism are controversial. We evaluated metabolic and cardiovascular parameters in differentiated thyroid carcinoma (DTC) patients with suppressed thyrotropin (TSH) due to levo-thyroxine (L-T4) therapy. We studied DTC patients and, as a control group, patients with a history of surgery for non-malignant thyroid pathology. Significantly higher insulin and lower HDL-cholesterol levels were recorded in DTC subjects. In both groups, insulin levels were significantly related with body mass index (BMI) but not with age or L-T4 dosage. In DTC patients, a significant negative correlation was seen between HDL-cholesterol and BMI or L-T4 dosage. In both groups, intima-media thickness (IMT) correlated positively with age, BMI, glucose levels and systolic blood pressure. In DTC patients, increased IMT was significantly correlated with glycated hemoglobin (HbA1c), cholesterol and triglycerides. In DTC patients, C-reactive protein correlated positively with insulin, insulin resistance, triglycerides and systolic blood pressure, and negatively with HDL-cholesterol. In both DTC and control subjects, fibrinogen correlated positively with age, BMI, increased IMT, HbA1c and systolic blood pressure. In DTC subjects, plasma fibrinogen concentrations correlated positively with insulin resistance, cholesterol and LDL-cholesterol, and negatively with TSH levels. Our data confirm that the favorable evolution of DTC can be impaired by a high incidence of abnormal metabolic and cardiovascular data that are, at least in part, related to L-T4 therapy. These findings underline the need for adequate L-T4 titration.

Effects of the hormones of the thyroid axis on the vitamin K-dependent plasma factors of blood coagulation (II, VII, IX, and X)

The hormonal regulation of haemostasis is a problem which has not received much attention. The data concerning the influence of hormones from the hypothalamic-pituitary-thyroid axis are scarce, contradictory and based mainly on clinical observations. The objective of the current research is to study the influence of the Thyrotropin releasing hormone (TRH), Thyroid stimulating hormone (TSH), Triiodothyronine (T3) and Thyroxin (T4) on the activity level of the vitamin K-dependent plasma factors of blood coagulation--factor II (F II), factor VII (F VII), factor IX (F IX) and factor X (F X). This study was carried out on 40 male Wistar rats. The necessary quantity of blood was obtained by cardiac puncture under ether narcosis. The indicators studied were activated partial thromboplastin time (aPTT), protothrombin time (PT), F II, F VII, F IX and F X, and were determined by means of Diagnostica Stago tests and with the help of an automatic coagulometer. The hormones studied were: TRH (0.06 mg/kg b.w.), TSH (1 MU/kg b.w.), T3 (0.08 mg/kg b.w.) T4 (0.08 mg/kg b.w.) prolonged aPTT (p<0.001) and PT (p<0.001). TRH and T3 significantly reduced the activity level of factors II, VII, IX and X; T4 only reduced the level of F II (p<0.05), and TSH did not induce significant changes in the haemocoagulation factors studied. The TRH, TSH, T3 and T4 hormones, although elements of one and the same axis, have an ambiguous effect on the vitamin K-dependent factors of blood coagulation. The results obtained show that the determined changes in the activity levels of the vitamin K-dependent plasma factors of blood coagulation are undoubtedly related to the hypocoagulation observed in the intrinsic and extrinsic pathways under the influence of the hormones of the thyroid axis.

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.

Clinical review: Thyroid dysfunction and effects on coagulation and fibrinolysis: a systematic review

CONTEXT

Various changes in the coagulation-fibrinolytic system have been described in patients with an excess or deficiency of thyroid hormones. The purpose of this systematic review is to summarize the effects of hyperthyroidism and hypothyroidism on these systems.

EVIDENCE ACQUISITION

All published case-control or interventional cohort studies that evaluated the effects of hyperthyroidism and hypothyroidism on the coagulation-fibrinolytic system in vivo were identified by a computer-assisted search of the MEDLINE and EMBASE electronic databases. A scoring system was used to divide studies into three quality categories: high, medium, and low quality.

EVIDENCE SYNTHESIS

A total of 36 papers were included. Because in several papers more than one case-control study or both a case-control and intervention study were described, a total of 39 case-control studies and 24 interventional cohort studies were analyzed. No high-quality study was identified. Three (7.7%) case-control and eight (33.3%) cohort studies were of medium quality. A total of 19 tests were investigated in the medium-quality studies. These tests revealed a hypocoagulable state for overt hypothyroidism and a hypercoagulable state for overt hyperthyroidism.

CONCLUSIONS

This analysis confirmed that clinically overt hyperthyroidism and hypothyroidism modify the coagulation-fibrinolytic balance, indicating that thyroid hormone excess or deficit is the probable main pathophysiological mechanism. Patients with overt hypothyroidism and overt hyperthyroidism appear to have an increased risk of bleeding and of thrombosis, respectively.

Review: The association of thyroid dysfunction with all-cause and circulatory mortality: is there a causal relationship?

CONTEXT

Currently there is ongoing debate on whether subclinical and overt thyroid dysfunction may exert deleterious effects on the cardiovascular system with the consequence of increased mortality in affected individuals. We systematically review studies on the relation of thyroid dysfunction with all-cause and circulatory mortality questioning whether thyroid dysfunction is a causal factor for mortality.

METHODS

Two investigators independently searched the MEDLINE database. All case-control and cohort studies published in peer-reviewed journals were selected. Studies on nonthyroidal illness or low-T3 syndrome and reports from highly selected populations were not considered. Risk estimates from studies with appropriate adjustment for confounders were metaanalyzed.

RESULTS

Four among eight studies performed to investigate the association between hyperthyroidism and mortality revealed an increased risk of either all-cause or circulatory mortality. Only the minority of studies, however, adjusted analyses for relevant confounders besides age, sex, and race. Studies after radioiodine therapy were generally biased by indication. Findings from 11 studies that investigated the relation between hypothyroidism and mortality were highly discrepant and partly even mutually exclusive. Some of these discrepancies are explained by confounding and selection.

CONCLUSIONS

The currently available evidence for a causal relation of both hyperthyroidism and hypothyroidism with mortality is weak and should particularly not be used to decide whether patients with subclinical thyroid conditions should be treated. Very old individuals might represent an exception from this rule and may benefit from mildly reduced thyroid function, but this has to be substantiated by further research.

Homocysteine and fibrinogen changes with L-thyroxine in subclinical hypothyroid patients

The aim of the present study was to evaluate plasma total homocysteine (Hcys) and serum fibrinogen concentrations in subclinical hypothyroid (SH) and overt hypothyroid patients before and after L-thyroxine (LT4) replacement and to compare them in euthyroid subjects. Fifteen SH and 20 hypothyroid premenopausal women were recruited in the study. We measured fasting plasma levels of Hcys and serum levels of free thyroxine (fT4), free triiodothyronine (fT3), thyrotropin (TSH), folate, vitamin B12, fibrinogen, renal functions, and lipid profiles in patients with SH and overt hypothyroid patients before and after LT4 treatment. Eleven healthy women were included in the study as a control group. Pretreatment Hcys levels were similar in SH and control subjects, whereas mean fibrinogen level of SH patients was higher than that of control subjects (p<0.05). Baseline Hcys (p<0.01) and fibrinogen (p<0.001) levels of the overt hypothyroid patients were significantly higher than those of the healthy subjects, and the pretreatment Hcys levels decreased with LT4 treatment (p<0.001). In conclusion, our data support that SH is not associated with hyperhomocysteinemia and Hcys does not appear to contribute to the increased risk for atherosclerotic disease in patients with SH.

Hypercholesterolemia and LDL receptor mRNA expression: modulation by selenium supplementation

Selenium (Se) status has been associated with cardiovascular disorders. Present study was aimed to elucidate the protective role of Se supplementation on LDL receptor (LDL-R) activity as well as mRNA expression during experimental hypercholesterolemia in SD male rats. Animals were fed 0.2 and 1 ppm Se supplemented control diet as well as 2% cholesterol supplemented diet for 3 months. LDL-R activity was measured in-vivo by injecting radiolabeled LDL to rats and decrease in counts per minute with time was taken as a measure of LDL clearance and in turn LDL-R activity. LDL-R mRNA expression was studied by RT-PCR. LDL-R activity and mRNA expression decreased significantly on 2% cholesterol supplemented diet feeding. On 1 ppm Se supplementation LDL-R activity as well as mRNA expression increased significantly. Present results demonstrate that Se supplementation upto 1 ppm is responsible for up regulation of LDL-R activity as well as mRNA expression, during hypercholesterolemia. These findings highlight the therapeutic potential of Se supplementation in lipid metabolism.

Elevated thrombin activatable fibrinolysis inhibitor (TAFI) antigen levels in overt and subclinical hypothyroid patients were reduced by levothyroxine replacement

The influence of hypothyroidism on haemostasis is an active research area. Not only bleeding tendency but also hypercoagulable states have been reported in hypothyroid patients. Decreased and increased fibrinolytic activity in hypothyroid patients has been shown in several studies. Thrombin activatable fibrinolysis inhibitor (TAFI) is an inhibitor of fibrinolysis, which has been recently isolated from human plasma. The aim of our study was to determine plasma TAFI antigen levels in overt and subclinical hypothyroidism, and to investigate the effect of levothyroxine treatment on TAFI levels. The study was performed in age- and sex-matched 30 overt hypothyroid, 30 subclinical hypothyroid patients, and 30 healthy controls. Blood samples were obtained from patients with overt and subclinical hypothyroidism before levothyroxine replacement, and one month after achieving a euthyroid state with levothyroxine. TAFI antigen levels were measured using Enzyme-Linked ImmunoSorbent Assay kits (Affinity Biologicals; Ontario, Canada). In baseline evaluation both the overt and subclinical hypothyroid groups had higher TAFI antigen levels than control group (p<0.05). High levels of TAFI antigen were correlated with the degree of thyroid failure. After achieving euthyroid state with levothyroxine replacement, TAFI antigen levels decreased significantly in patients with overt and subclinical hypothyroidism (p<0.05). Our data suggest that there are elevated plasma levels of TAFI antigen both in overt and subclinical hypothyroidism, which may be associated with hypofibrinolysis and elevated risk of thrombosis. Normalization of thyroid state by levothyroxine replacement seems to be effective in lowering of TAFI antigen levels in hypothyroidism.

Relationship of thyroid stimulating hormone with coronary atherosclerosis in angina patients

BACKGROUND

In the previous recent reports, subclinical hypothyroidism is an independent risk factor for acute myocardial infarction in elderly women. It was not established whether a normal range of thyroid stimulating hormone (TSH) influences the presence of coronary atherosclerosis. We postulated that the level of TSH is risk factor of coronary atherosclerosis in angina patients who have normal thyroid function.

METHODS

We studied 344 angina patients (62.5+/-9.72 years, male 50%) who underwent elective coronary angiography. TSH, free thyroxine, serum lipid levels and high-sensitivity C-reactive protein levels were measured and compared to the severity of coronary artery disease.

RESULTS

In patients with high level of TSH (> or =2.1 microIU/mL), age (p=0.016), the levels of serum creatinine (p=0.004) and Gensini's score (p=0.016) were significantly higher than those in patients with low TSH levels. The incidence of multi-vessel disease was higher in patients with high TSH level (p=0.026). TSH level showed a significant correlation with age (r=0.109, p=0.044) and Gensini's score (r=0.117, p=0.045). The multivariate analysis revealed that age (OR 2.39, p=0.001), diabetes (OR 3.74, p=0.001), creatinine (OR 2.06, p=0.008), and smoking (OR 1.85, p=0.045) were independent predictors for significant coronary artery disease, but TSH level did not predict coronary artery stenosis.

CONCLUSIONS

Although the high level of serum TSH is associated with multi-vessel disease, it was not the determinant of coronary artery disease in patients with normal range of thyroid function.

L'hypothyroïdie fruste est-elle un facteur de risque cardiovasculaire ?

OBJECTIVES

Subclinical hypothyroidism defined by the presence of elevated TSH levels but normal free T4 level is a common situation. Its consequences on health are yet on debate and the interest of a precocious treatment remains surrounded by controversy.

KEY POINTS

The relationship between subclinical hypothyroidism and cardiovascular disease has been evaluated by several cross-sectional and longitudinal studies. Subclinical hypothyroidism has direct but subtle effects on the heart function, on the peripheral vascular resistance, and is associated with a mild elevation of LDL-cholesterol levels; all abnormalities may be partly reversed by a thyroxine supplementation. Data of the literature give insufficient evidence as to whether subclinical hypothyroidism is an independent cardiovascular risk factor. However treatment of subjects with TSH levels up or near to 10 mU/l would probably be beneficial in the prevention of cardiovascular disease.

FUTURE PROSPECTS

Based on observational and interventional studies there are some arguments on the benefit of euthyroidism restoration only in patients with TSH levels superior to 10 mU/l.