Coronary-artery disease in hypothyroidism. Observations in clinical myxoedema

Causal effect of gut microbiota of Defluviitaleaceae on the clinical pathway of "Influenza-Subacute Thyroiditis-Hypothyroidism"

Introduction

Hypothyroidism has been found to be influenced by gut microbiota. However, it remains unclear which a taxon of gut microbiota plays a key role in this function. Identifying the key bacteria affects hypothyroidism and through what mechanism will be helpful for the prevention of hypothyroidism through specific clinical pathways.

Materials and methods

In Study A, 35 families and 130 genera of gut microbiota are used as exposures, with hypothyroidism as the outcome. The causal effect of the gut microbiota on hypothyroidism is estimated through two-sample Mendelian randomization. Combining the results of the two taxonomical levels, key taxa are selected, which in Study B are investigated for their causal association with multiple generally admitted causes of hypothyroidism and their more upstream factors. For validating and revealing the potential mechanism, enrichment analyses of the related genes and interacting transcription factors were performed.

Results

In Study A, Defluviitaleaceae (OR: 0.043, 95% CI: 0.005-0.363, P = 0.018)/Defluviitaleaceae_UCG_011 (OR: 0.385, 95% CI: 0.172-0.865, P = 0.021) are significantly causally associated with hypothyroidism at both taxonomical levels. In Study B, Defluviitaleaceae family and Defluviitaleaceae_UCG_011 genus show the causal association with decreased thyroiditis (Family: OR: 0.174, 95% CI: 0.046-0.653, P = 0.029; Genus: OR: 0.139, 95% CI: 0.029-0.664, P = 0.043), decreased subacute thyroiditis (Family: OR: 0.028, 95% CI: 0.004-0.213, P = 0.007; Genus: OR: 0.018, 95% CI: 0.002-0.194, P = 0.013), decreased influenza (Family: OR: 0.818, 95% CI: 0.676-0.989, P = 0.038; Genus: OR: 0.792, 95% CI: 0.644-0.974, P = 0.027), and increased anti-influenza H3N2 IgG levels (Family: OR: 1.934, 95% CI: 1.123-3.332, P = 0.017; Genus: OR: 1.675, 95% CI: 0.953-2.943, P = 0.073). The results of the enrichment analysis are consistent with the findings and the suggested possible mechanisms.

Conclusion

Defluviitaleaceae of the gut microbiota displays the probability of causally inhibiting the clinical pathway of "Influenza-Subacute Thyroiditis-Hypothyroidism" and acts as the potential probiotics to prevent influenza, subacute thyroiditis, and hypothyroidism.

Hypothyroidism and Risk of Cardiovascular Disease

Thyroid hormones (TH) have a significant impact on cellular oxidative metabolism. Besides that, they maintain vascular homeostasis by positive effects on endothelial and vascular smooth muscle cells. Subclinical (SCH) and clinical (CH) hypothyroidism influences target organs by changing their morphology and function and impaired blood and oxygen supply induced by accelerated atherosclerosis. The increased risk of acceleration and extension of atherosclerosis in patients with SCH and CH could be explained by dyslipidemia, diastolic hypertension, increased arterial stiffness, endothelial dysfunction, and altered blood coagulation. Instability of atherosclerotic plaque in hypothyroidism could cause excessive activity of the elements of innate immunity, which are characterized by: the significant presence of macrophages in atherosclerotic plaques, increased nuclear factor kappa B (NFkB) expression, and elevated levels of tumor necrosis factor α (TNF-α) and matrix metalloproteinase (MMP) 9, with reduced interstitial collagen, which all together creates inflammation milieu resulted in plaque rupture. Optimal substitution by levothyroxine (LT4) restores biochemical euthyroidism. In postmenopausal women and elderly patients with hypothyroidism and associated vascular comorbidity, excessive LT4 substitution could lead to atrial rhythm disorders and osteoporosis. Therefore, it is of interest to maintain thyroid-stimulating hormone (TSH) levels in the reference range, thus eliminating the deleterious effects of lower or higher TSH levels on the cardiovascular system. This review summarizes the recent literature on subclinical and clinical hypothyroidism and atherosclerotic cardiovascular disease and discusses the effects of LT4 replacement therapy on restoring biochemical euthyroidism and atherosclerosis processes.

The Role of Thyroid Diseases and their Medications in Cardiovascular Disorders: A Review of the Literature

The association between thyroid disease and cardiovascular manifestations is significant and undeniable. Previous studies have explained several aspects of the effects of thyroid hormone on the heart and cardiovascular system. Accordingly, both hyper and hypothyroidism can cause important alterations in cardiac rhythm, output and contractility as well as vascular resistance and blood pressure. Since treating the thyroid abnormality, especially in its initial stages, could lead to a significant improvement in most of its resultant cardiovascular disturbances, early suspicion and recognition of thyroid dysfunction, is necessary in patients with cardiovascular manifestations. In this in-depth review, we discuss the physiological roles as well as the effects of abnormal levels of thyroid hormones on the cardiovascular system. We also review the effects of the medications used for the treatment of hyper and hypothyroidism on cardiac function. In the end, we discuss the association between thyroid function and amiodarone, an effective and frequently-used antiarrhythmic drug, because of its well-known effects on the thyroid.

Association between type 2 diabetes mellitus and hypothyroidism: a case-control study

Objectives

Type 2 diabetes mellitus (DM-II) is highly prevalent in Saudi Arabia and only few studies have assessed it as a risk factor for hypothyroidism. This study aimed to examine the association between DM-II and hypothyroidism.

Subjects and methods

We conducted a hospital-based case-control study. As cases, we included all adults admitted to King Abdulaziz University Hospital (KAUH) with laboratory-confirmed hypothyroidism. As controls, we drew a random sample of patients admitted to the orthopedic clinic at KAUH with laboratory-confirmed absence of hypothyroidism. We extracted data from the medical records regarding age, sex, presence of DM-II, HbA1c, comorbidities, treatment, and complications. We used multivariate logistic regression to identify factors associated with hypothyroidism.

Results

We included 121 cases and 121 controls. In comparison to controls, cases were older (P=0.005), had higher prevalence of DM-II (P<0.001), had higher levels of HbA1c (P=0.03), used insulin (P<0.001) and oral hypoglycemic drugs (P<0.001) more often, and suffered more often from hypertension (P<0.001), coronary artery disease (CAD) (P<0.001), stroke (P=0.04), diabetic foot (P<0.001), and nephropathy (P<0.001). According to multivariate regression, the risk of hypothyroidism was significantly increased among patients with DM-II (OR=4.14; 95% CI=20.20-7.80; P<0.001) and CAD (OR=14.15; 95% CI=1.80-111.43; P=0.01).

Conclusion

Patients with DM-II were at increased risk of developing hypothyroidism. Adequate management and control of DM-II might reduce the risk of developing hypothyroidism. Further research using a prospective cohort study design is needed to confirm these findings.

Key messages

Patients with DM-II had an increased risk of developing hypothyroidism.

Hypothyroidism

Hypothyroidism is a common condition of thyroid hormone deficiency, which is readily diagnosed and managed but potentially fatal in severe cases if untreated. The definition of hypothyroidism is based on statistical reference ranges of the relevant biochemical parameters and is increasingly a matter of debate. Clinical manifestations of hypothyroidism range from life threatening to no signs or symptoms. The most common symptoms in adults are fatigue, lethargy, cold intolerance, weight gain, constipation, change in voice, and dry skin, but clinical presentation can differ with age and sex, among other factors. The standard treatment is thyroid hormone replacement therapy with levothyroxine. However, a substantial proportion of patients who reach biochemical treatment targets have persistent complaints. In this Seminar, we discuss the epidemiology, causes, and symptoms of hypothyroidism; summarise evidence on diagnosis, long-term risk, treatment, and management; and highlight future directions for research.

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.

Thyroid Hormone and Vascular Remodeling

Both hyperthyroidism and hypothyroidism affect the cardiovascular system. Hypothyroidism is known to be associated with enhanced atherosclerosis and ischemic heart diseases. The accelerated atherosclerosis in the hypothyroid state has been traditionally ascribed to atherogenic lipid profile, diastolic hypertension, and impaired endothelial function. However, recent studies indicate that thyroid hormone has direct anti-atherosclerotic effects, such as production of nitric oxide and suppression of smooth muscle cell proliferation. These data suggest that thyroid hormone inhibits atherogenesis through direct effects on the vasculature as well as modification of risk factors for atherosclerosis. This review summarizes the basic and clinical studies on the role of thyroid hormone in vascular remodeling. The possible application of thyroid hormone mimetics to the therapy of hypercholesterolemia and atherosclerosis is also discussed.

Hypothyroidism Is Associated With Coronary Endothelial Dysfunction in Women

BACKGROUND

Hypothyroidism is associated with an increased risk of coronary artery disease, beyond that which can be explained by its association with conventional cardiovascular risk factors. Coronary endothelial dysfunction precedes atherosclerosis, has been linked to adverse cardiovascular events, and may account for some of the increased risk in patients with hypothyroidism. The aim of this study was to determine whether there is an association between epicardial and microvascular coronary endothelial dysfunction and hypothyroidism.

METHODS AND RESULTS

In 1388 patients (mean age 50.5 [12.3] years, 34% male) presenting with stable chest pain to Mayo Clinic, Rochester, MN for diagnostic coronary angiography, and who were found to have nonobstructive coronary artery disease (<40% stenosis), we invasively assessed coronary artery endothelial-dependent microvascular and epicardial function by evaluating changes in coronary blood flow (% Δ CBF Ach) and diameter (% Δ CAD Ach), respectively, in response to intracoronary infusions of acetylcholine. Patients were divided into 2 groups: hypothyroidism, defined as a documented history of hypothyroidism or a thyroid-stimulating hormone (TSH) >10.0 mU/mL, n=188, and euthyroidism, defined as an absence of a history of hypothyroidism in the clinical record and/or 0.3<TSH≤10.0 mU/mL, n=1200. Subjects with a history of hypothyroidism had a significantly lower % Δ CBF Ach (48.26 [80.66] versus 64.58 [128.30]) compared to patients with euthyroidism, while the % Δ CAD Ach did not vary significantly between groups. After adjusting for covariates, females with hypothyroidism still had a significantly lower % Δ CBF Ach (estimated difference in % Δ CBF Ach [SE]: -16.79 [8.18]).

CONCLUSIONS

Hypothyroidism in women is associated with microvascular endothelial dysfunction, even after adjusting for confounders, and may explain some of the increased risk of cardiovascular disease in these patients.

Effects of levothyroxine treatment on insulin sensitivity, endothelial function and risk factors of atherosclerosis in hypothyroid women

OBJECTIVES

Contradictory results are encountered in literature regarding the effects of hypothyroidism on the risk factors of atherosclerosis. We aimed to explore the changes in atherosclerotic risk factors and insulin sensitivity before and after levothyroxine replacement therapy in women with primary hypothyroidism and compare with that of healthy controls.

PATIENTS AND METHODS

Twelve patients (mean age of 34±11.7years) without an evident disease except for primary hypothyroidism (TSH≥20mIU/L) and eleven euthyroid, age-matched (33.8±8.4years) female volunteers as controls were included. Baseline thyroid hormones, lipid parameters, homocysteine, fibrinogen levels were measured in both groups. Flow-mediated endothelial-dependent vasodilatation (FMD) method was used to evaluate endothelial dysfunction. Insulin sensitivity was assessed by M values based on euglycemic hyperinsulinemic clamp technique. The same measurements were performed after 6months of levothyroxine treatment and recovery of euthyroid state in hypothyroid patients.

RESULTS

Treatment reduced total cholesterol (P<0.005), LDL-cholesterol (P<0.005), lipoprotein(a) (P<0.01), fibrinogen (P<0.0001) and homocysteine (P<0.0005) levels. Treatment significantly improved M values of hypothyroid patients (3.68±1.53mg/kg.min vs 6.02±1.21mg/kg.min, P<0.0001) and FMD (9.1±3.7% vs 16.4±4.4%, hypothyroid vs euthyroid, P<0.0001). Significant correlations were found between M values and TSH (r=-0.6, P<0.005), fibrinogen (r=-0.53, P<0.01) measurements, free T3 (r=0.51, P<0.02) and free T4 (r=0.49, P<0.02) levels. FMD was significantly correlated with fibrinogen levels (r=-0.49, P<0.05).

CONCLUSION

Insulin resistance, endothelial dysfunction, atherosclerotic risk markers improves with treatment of hypothyroidism.

Thyroid and aging or the aging thyroid? An evidence-based analysis of the literature

Thyroid hormone production, metabolism, and action change with aging. The reference ranges for serum thyrotropin and thyroid hormones are derived mainly from younger populations. Thus, the prevalence of subclinical thyroid dysfunction is increased greatly in the elderly. However, it is unclear whether mild thyroid dysfunction in the elderly is associated with adverse outcomes. In this review, we discuss current evidence-based literature on thyroid function in the elderly and whether subclinical thyroid dysfunction in the elderly should be treated.

Hypothyroidism Complicated by Angina Pectoris: Therapeutic Approaches

The association of hypothyroidism and coronary artery disease is not uncommon. The precipitation of angina pectoris, cardiac arrhythmia, and even myocardial infarction may occur in patients when initiating rapid replacement therapy for hypothyroidism. This is particularly true when replacement therapy is instituted in elderly persons or in patients with preexisting coronary artery disease. A starting daily dose of 12.5 to 25 micrograms and increments of 25 micrograms every 2 to 3 weeks is recommended. Close monitoring of cardiac symptoms is essential to avoid side effects. Medical management of angina pectoris includes administration of beta-blockers, nitrates, or at times combination antianginal therapy may be most effective. Persistence of angina in these patients may require coronary angiography with subsequent angioplasty or coronary artery bypass surgery.

Effect of L-thyroxine replacement on apolipoprotein B-48 in overt and subclinical hypothyroid patients

Apolipoprotein B-48 (ApoB-48) is a constituent of chylomicrons and chylomicron remnants, and is thought to be one of the risk factors for atherosclerosis. We evaluated the effect of L-thyroxine (L-T(4)) replacement on serum ApoB-48 levels in patients with primary hypothyroidism. Eighteen patients with overt hypothyroidism (OH) and 18 patients with subclinical hypothyroidism (SH) participated in the study. The lipid profiles, including ApoB-48, were measured in patients with hypothyroidism before and 3 months after L-T(4) replacement. After L-T(4) replacement, the serum concentrations of all lipoproteins, exclusive of lipoprotein(a) (Lp(a)), were significantly decreased in patients with OH. In patents with SH, the serum levels of total cholesterol (TC), non-high-density lipoprotein cholesterol (non-HDL-C), remnant-like particle cholesterol (RLP-C), apolipoprotein B (ApoB), and ApoB-48 decreased significantly after L-T(4) replacement. The serum levels of triglycerides (TG), HDL-C, low-density lipoprotein cholesterol (LDL-C), apolipoprotein A1 (ApoA-1), and Lp(a) did not change significantly. In all 36 patients, the reduction in the ApoB-48 levels correlated significantly with the reduction in TSH levels (r = 0.39, P<0.05). This study showed clearly that L-T(4) replacement might reduce serum levels of ApoB-48 in both OH and SH patients. Such altered serum levels of ApoB-48 in patients with OH and SH may be related to the disturbed metabolism of chylomicron remnants in patients with hypothyroidism.

Thyroid hormone replacement therapy for primary hypothyroidism leads to significant improvement of renal function in chronic kidney disease patients

BACKGROUND

The interactions between kidney and thyroid functions have been known for many years; however, there are few studies on the extent of the improvements and long-term changes of renal function after thyroid hormone replacement therapy (THRT) in chronic kidney disease (CKD) patients. The purpose of this study was to determine how THRT affects the estimated glomerular filtration rate (eGFR) in CKD patients with primary hypothyroidism.

METHODS

A retrospective investigation was performed on 51 Japanese patients (15 men and 36 women) with primary hypothyroidism. The changes in eGFR after THRT were examined according to the existence of CKD and severity of thyroid function.

RESULTS

eGFR increased rapidly over the first 6 months after THRT in CKD patents, which was followed by a plateau. There was a correlation between eGFR and the severity of hypothyroidism, which was independent of age, and eGFR in severely hypothyroid patients significantly increased up to levels that were similar to mildly hypothyroid patients after THRT. eGFR improved more in the lower initial eGFR group and increased about 30 % in CKD patients (47.5 ± 7.7 vs. 62.1 ± 9.5 ml/min/1.73 m(2), P < 0.01). Moreover, eGFR in CKD patients with mild to moderate hypothyroidism was significantly increased compared to that in non-CKD patients.

CONCLUSION

Our data suggested that hypothyroidism contributed to the reduction in eGFR, especially in CKD patients; therefore, patients with CKD should positively be examined for thyroid function, and appropriate THRT should be started if needed.

Preservation of renal function by thyroid hormone replacement therapy in chronic kidney disease patients with subclinical hypothyroidism

CONTEXT

Subclinical hypothyroidism is not a rare condition, but the use of thyroid hormone to treat subclinical hypothyroidism is an issue of debate.

OBJECTIVE

This study was undertaken to investigate the impact of thyroid hormone therapy on the changes in estimated glomerular filtration rate (eGFR) in subclinical hypothyroidism patients with stage 2-4 chronic kidney disease.

PATIENTS

A total of 309 patients were included in the final analysis.

MAIN OUTCOME MEASURE

The changes in eGFR over time were compared between patients with and without thyroid hormone replacement therapy using a linear mixed model. Kaplan-Meier curves were constructed to determine the effect of thyroid hormone on renal outcome, a reduction of eGFR by 50%, or end-stage renal disease. The independent prognostic value of subclinical hypothyroidism treatment for renal outcome was ascertained by multivariate Cox regression analysis.

RESULTS

Among the 309 patients, 180 (58.3%) took thyroid hormone (treatment group), whereas 129 (41.7%) did not (nontreatment group). During the mean follow-up duration of 34.8 ± 24.3 months, the overall rate of decline in eGFR was significantly greater in the nontreatment group compared to the treatment group (-5.93 ± 1.65 vs. -2.11 ± 1.12 ml/min/yr/1.73 m(2); P = 0.04). Moreover, a linear mixed model revealed that there was a significant difference in the rates of eGFR decline over time between the two groups (P < 0.01). Kaplan-Meier analysis also showed that renal event-free survival was significantly lower in the nontreatment group (P < 0.01). In multivariate Cox regression analysis, thyroid hormone replacement therapy was found to be an independent predictor of renal outcome (hazard ratio, 0.28; 95% CI, 0.12-0.68; P = 0.01).

CONCLUSION

Thyroid hormone therapy not only preserved renal function better, but was also an independent predictor of renal outcome in chronic kidney disease patients with subclinical hypothyroidism.

Role of surrogate markers of atherosclerosis in clinical and subclinical thyroidism

Background. Data on the relationship between homocysteine, plasminogen activator inhibitor 1, hs-CRP, fibrinogen, and carotid intima media thickness (CA-IMT) is plenty but contradicting and the majority of the studies investigated this issue in only specific thyroidism groups. The aim of this paper was to investigate these relations in patients with subclinical and clinical hypo- and hyperthyroidism. Methods. In this cross-sectional study, 16 patients from each thyroidism group and 20 healthy cases were enrolled. Fibrinogen levels and plasminogen activator inhibitor 1 (PAI-1) activity were assessed. CA-IMT was determined by gray-scale high-resolution color Doppler ultrasound. Results. Serum homocysteine levels were higher in hypothyroidic patients compared to the control (P = 0.003). Fibrinogen levels were higher in patients with subclinical hypothyroidism compared to other groups (P < 0.05). There was no difference between groups regarding PAI-1. Whereas total cholesterol, homocysteine, and LDL were correlated with CAIMT, hs-CRP, PAI-1, and fibrinogen were not. In the clinical hypothyroidism group, the correlation of homocysteine with CA-IMT was derived from the correlation between CA-IMT and homocysteine. Conclusions. Homocysteine and fibrinogen levels are higher in patients with clinical and subclinical hypothyroidism, respectively. Homocysteine level is associated with CA-IMTonly in patients with clinical hypothyroidism.

Changes in cerebral blood flow velocity in patients with hypothyroidism

BACKGROUND

At present, hypothyroidism is a well-known risk factor for cardiovascular disorders. The aim of this study was to assess the effects of hypothyroidism on cerebral blood flow velocity with transcranial Doppler (TCD) ultrasonography.

DESIGN AND METHODS

In this study, 30 subjects were enrolled for clinical, subclinical, and healthy control groups. Bilateral middle cerebral artery (MCA) peak-systolic, end-diastolic, and mean blood flow velocities; Gosling's pulsatility index values; and Pourcelot's resistance index values were recorded and compared with each other. TCD was performed in clinical hypothyroid patients after they became euthyroid with thyroid hormone replacement therapy (HRT). The initial and post-HRT results for the clinical hypothyroid group were then compared and evaluated.

RESULTS

There were 30 subjects in each group. Men/women ratio and mean age in clinical hypothyroid, subclinical hypothyroid, and control groups were 3/27, 4/26, and 5/25, and 37.4, 34.4, and 36.7 respectively. Peak-systolic, end-diastolic, and mean blood flow velocities of bilateral MCA were similar in clinical and subclinical hypothyroid groups but significantly higher when compared with the control group. After adequate thyroid HRT in clinical hypothyroid group, the peak-systolic, end-diastolic, and mean blood flow velocities were significantly decreased.

CONCLUSIONS

Increased cerebral blood flow velocities were observed in clinical and subclinical patients with hypothyroidism. The normalization of increased blood flow velocity with thyroid HRT suggests a reversible condition.

Associations of triiodothyronine levels with carotid atherosclerosis and arterial stiffness in hemodialysis patients

BACKGROUND AND OBJECTIVES

End-stage renal disease is linked to alterations in thyroid hormone levels and/or metabolism, resulting in a high prevalence of subclinical hypothyroidism and low triiodothyronine (T3) levels. These alterations are involved in endothelial damage, cardiac abnormalities, and inflammation, but the exact mechanisms are unclear. In this study, we investigated the relationship between serum free-T3 (fT3) and carotid artery atherosclerosis, arterial stiffness, and vascular calcification in prevalent patients on conventional hemodialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

137 patients were included. Thyroid-hormone levels were determined by chemiluminescent immunoassay, carotid artery-intima media thickness (CA-IMT) by Doppler ultrasonography, carotid-femoral pulse wave velocity (c-f PWV), and augmentation index by Sphygmocor device, and coronary artery calcification (CAC) scores by multi-slice computerized tomography.

RESULTS

Mean fT3 level was 3.70 ± 1.23 pmol/L. Across decreasing fT3 tertiles, c-f PWV and CA-IMT values were incrementally higher, whereas CACs were not different. In adjusted ordinal logistic regression analysis, fT3 level (odds ratio, 0.81; 95% confidence interval, 0.68 to 0.97), age, and interdialytic weight gain were significantly associated with CA-IMT. fT3 level was associated with c-f PWV in nondiabetics but not in diabetics. In nondiabetics (n = 113), c-f PWV was positively associated with age and systolic BP but negatively with fT3 levels (odds ratio = 0.57, 95% confidence interval 0.39 to 0.83).

CONCLUSIONS

fT3 levels are inversely associated with carotid atherosclerosis but not with CAC in hemodialysis patients. Also, fT3 levels are inversely associated with surrogates of arterial stiffness in nondiabetics.

Impaired endothelial- and nonendothelial-mediated vasodilation in patients with acute or chronic hypothyroidism

OBJECTIVE

Vascular dysfunction and accelerated atherosclerosis are prominent features of hypothyroidism. The relative roles of thyroid hormone (TH) deficiency and the associated vascular risk conditions are still unclear. We studied the impact of acute and chronic hypothyroidism on vascular reactivity.

PATIENTS

We studied 12 patients with chronic primary hypothyroidism (cHY; TSH: 52 +/- 14 mU/l), seven patients with acute hypothyroidism secondary to total thyroidectomy (aHY; TSH: 97 +/- 24) and 13 healthy subjects (TSH: 1.2 +/- 0.5).

MEASUREMENTS

We measured forearm blood flow (FBF) using plethysmography during intra-brachial infusion of: acetylcholine (ACh), sodium nitroprusside (NP) and norepinephrine (NE). We also measured serum C-reactive protein (CRP), TNF-alpha, asymmetric dimethylarginine (ADMA) and the forearm balance of nitric oxide (NO) during ACh infusion.

RESULTS

As compared with the controls, the vasodilatory response to ACh was reduced in cHY (P = 0.001) and aHY (P = 0.04), as was the forearm release of NO (P < 0.05). During NP infusion, FBF rose to 24 +/- 2 ml/dl/min in the controls and to significantly lower values in cHY (12 +/- 1; P = 0.001) and aHY (15 +/- 2; P = 0.004). NE-induced vasoconstriction was similar in the controls and aHY, but blunted in cHY. Serum CRP, TNF-alpha and ADMA were not different in the three groups.

CONCLUSIONS

(i) Hypothyroidism associates with endothelial and nonendothelial mediated vascular dysfunction; (ii) these defects are evident even after short-term hypothyroidism, indicating that TH deficiency per se is sufficient to alter vascular homeostasis; and (iii) chronic, but not acute, hypothyroidism impairs the vasoconstrictory effect of NE in the resistance vessels.

Changes in left ventricular function and remodeling after myocardial infarction in hypothyroid rats

It has been shown that hypothyroidism may lead to delayed wound healing after experimental myocardial infarction (MI) in rats and increased infarct size in dogs. However, the long-term effect of hypothyroidism on left ventricular (LV) remodeling after MI has not been determined. Adult female Sprague-Dawley rats with and without surgical thyroidectomy (TX) were used in the study. Four weeks after TX, MI or sham MI was performed on TX and non-TX rats. Rats from all groups were examined 4 wk later. Four weeks after TX, hypothyroid-induced LV dysfunction was confirmed by echocardiography. In terminal experiments 4 wk after MI, TX sham-MI rats showed smaller hearts and impaired LV function compared with non-TX sham-MI controls. TX + MI rats showed smaller hearts with bigger infarct areas, higher LV end-diastolic pressures, and greater impairment of relaxation (−dP/d t) compared with non-TX MI rats. Relative changes after MI between TX and non-TX rats for most other hemodynamic and echocardiographic indexes were similar. These results suggest that preexisting hypothyroidism exaggerates post-MI remodeling and worsens LV function, particularly diastolic function.

Hypothyroidism is associated with signs of endothelial dysfunction despite 1-year replacement therapy with levothyroxine

OBJECTIVE

Hypothyroidism is associated with elevated cardiovascular risk, not fully explained by classical risk factors. Instead, endothelial dysfunction may link hypothyroidism to atherosclerosis. The effect of levothyroxine substitution on endothelial function has been sparsely studied and the results are unclear. This study tested endothelial function as estimated by concomitant measurements of endothelial dependent vascular dilatory capacity and plasma concentration of von Willebrand factor antigen in patients with hypothyroidism and further examined the impact of subsequent levothyroxine substitution.

DESIGN AND PATIENTS

Sixteen consecutive patients (13 women, 3 men, aged 46 +/- 11 years) with hypothyroidism were included and compared to 16 matched healthy controls (13 women, 3 men, aged 49 +/- 11 years). Patients with hypothyroidism were reexamined after 3, 6 and 12 months of levothyroxine substitution.

MEASUREMENTS

Dilatory responses of the brachial artery to post-ischaemic increased blood flow (endothelium-dependent flow-associated dilatation) and to nitroglycerin (endothelium-independent nitroglycerin induced dilatation) were measured by ultrasound. Plasma concentrations of von Willebrand factor antigen were measured by ELISA.

RESULTS

Flow-associated dilatation was impaired in patients with hypothyroidism as compared to controls (102.7 +/- 3.6 vs. 105.6 +/- 3.8%, P = 0.04) whereas no differences in plasma concentration of von Willebrand factor antigen were found. One year levothyroxine substitution did not improve flow-associated dilatation and was associated with an increase of the plasma von Willebrand factor antigen concentration.

CONCLUSIONS

Hypothyroid patients are characterized by endothelial dysfunction sustained despite long-term levothyroxine substitution and potentially increasing the risk of atherosclerosis. Different estimates of endothelial dysfunction seem unequally influenced by hypothyroidism.

Changes in endothelial function and its association with plasma osteoprotegerin in hypothyroidism with exercise-induced silent myocardial ischaemia

OBJECTIVE

Hypothyroidism is associated with an increased risk for cardiovascular disease. Exercise-induced silent myocardial ischaemia (SI) is an early stage of coronary artery disease. Recently, many studies have shown that endothelial dysfunction is an early physiological event in atherosclerosis, and osteoprotegerin (OPG) acts as an important regulatory molecule in the vasculature. The aim of this study was to investigate the alteration of endothelial function and its association with plasma OPG in hypothyroidism with SI.

METHODS

Forty-eight female postmenopausal hypothyroid patients with normal rest electrocardiography (ECG) were selected. Of these, 19 cases had SI. Twenty healthy females without SI were selected as controls. High-resolution ultrasound was used to measure brachial artery diameter at rest, after reactive hyperaemia and after sublingual glyceryltrinitrate (GTN). Plasma OPG concentration was measured in duplicate by a sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

Flow-mediated arterial dilation (FMD) in the total hypothyroid group, the hypothyroidism with SI group and the hypothyroidism without SI group was 3.51 +/- 0.62%, 3.20 +/- 0.54% and 3.72 +/- 0.60%, respectively, significantly lower than that in the controls (5.08 +/- 0.61%) (P < 0.01). Compared with the hypothyroidism without SI group, FMD in the hypothyroidism with SI group was significantly lower (P < 0.05). Plasma OPG levels in the total hypothyroid group, patients with SI and patients without SI were significantly higher than in the control group (P < 0.05). Compared with patients without SI, OPG levels were significantly higher in patients with SI (P < 0.05). On multiple regression analysis, low density lipoprotein cholesterol (LDL-C), lipoprotein (a) [Lp(a)], C-reactive protein (CRP), OPG, TSH, free T3 (FT3) and thyroid peroxidase antibody (TPO-Ab) were found to be significant factors that were associated with FMD. Logistic analysis also showed that LDL-C, TSH, OPG, CRP and FMD were independently and significantly associated with SI in hypothyroidism.

CONCLUSION

Impaired endothelial function and increased levels of OPG exist in hypothyroid patients, especially those with SI. These findings support the growing concept that endothelial dysfunction may be associated with vascular disease, and subsequently elevated plasma OPG may have a role in the development of vascular dysfunction in hypothyroid patients.

Lack of significant association between intima-media thickness in the carotid artery and serum TSH level. The Tromsø Study

BACKGROUND

Increased arterial wall intima-media thickness (IMT) is an early feature of atherosclerosis and has been reported to be altered in patients with thyroid dysfunction. The present study was performed to examine the relation between carotid artery intima-media thickness and possible variations in thyroid function in normal subjects using serum TSH as a surrogate index of thyroid function.

DESIGN

A total of 2034 subjects (974 males) were studied, 1856 or whom were non-users of thyroxine. The subjects not taking thyroxine were classified into three groups, those with a low serum TSH (0.48 mIU/L (2.5 percentile, those with serum TSH from 0.48 to 4.16 mIU/L, and those with high serum TSH of >4.16 mIU/L (97.5 percentile). Carotid ultrasound was performed in each all 2034 subjects to determine IMT.

RESULTS

Among those not taking thyroxine, subjects in the low serum TSH group had a higher mean IMT as compared to those in the normal and high serum TSH groups but the differences were not significant when adjusted for gender, age, smoking status, body mass index, systolic blood pressure and serum cholesterol (0.88 +/- 0.15 mm, 0.84 +/- 0.16 mm, and 0.84 +/- 0.24 mm respectively). Subjects taking thyroxine had significantly higher IMT than those not taking thyroxine (0.89 + 0.20 mm versus 0.84 + 0.17 mm, p<0.01).

CONCLUSIONS

No significant relationship between carotid IMT and serum TSH levels was observed in normal, non thyroxine taking, subjects. Carotid IMT was increased in subjects taking thyroxine. Whether the increase in carotid IMT is due to thyroxine ingestion or underlying thyroid disease cannot be answered from the study.

Cardiovascular risk in elderly hypothyroid patients

Overt hypothyroidism (OH) and subclinical hypothyroidism (SH) are frequently found in the elderly. OH is associated with several functional cardiovascular abnormalities and increased risk of atherosclerosis resulting from hypertension associated to atherogenic lipid profile. Other potential atherogenic factors involved in OH are increased circulating C-reactive protein and homocysteine, increased arterial stiffness, endothelial dysfunction, and altered coagulation parameters. Similar (although mild) cardiovascular abnormalities are present in SH. Since all these abnormalities regress with levothyroxine (L-T4) administration, the cardiovascular benefits of replacement therapy in OH are not questionable, independently from the patient's age or the presence of coexisting cardiovascular disease. On the other hand, in spite of a very large number of studies, no consensus has been reached so far about the actual cardiovascular and/or general health impact of SH, and different recommendations have been recently made about screening and treatment of this condition. Although divergent results have been obtained in several epidemiological studies, recent meta-analyses provide evidence for a slight but significant increase of coronary heart disease (CHD) risk in SH. However, no agreement has been reached in favor or against active screening and/or treatment of mild thyroid failure. Moreover, L-T4 therapy is discouraged in aged subjects, because the increased oxygen consumption consequent to thyroid hormone administration could be dangerous, especially in the presence of coexisting CHD. In keeping with this concept are recent data showing reduced mortality risk in untreated mild hypothyroid subjects aged >85 years, suggesting that some degree of decreased thyroid activity at the tissue level might have favorable effects in the oldest-old. However, the effects of subtle thyroid dysfunction may be different in different age ranges. Since the main studies supporting a role for SH as a risk factor for atherosclerosis, cardiovascular disease, and all-cause mortality have been carried out in populations aged > or =55-60 years, mild thyroid failure could concur to increased cardiovascular risk in middle-aged and "young elderly" subjects, while being devoid of detrimental effects and possibly protective in the oldest-old. Further studies are needed to confirm this hypothesis.

Carotid artery intima media thickness is inversely related to serum free thyroxine in euthyroid subjects

OBJECTIVE

The effect of thyroid function on cardiovascular risk may extend to the euthyroid range. In euthyroid subjects, we determined whether carotid artery intima media thickness (IMT), a measure of subclinical atherosclerosis, is related to thyroid function.

DESIGN AND SUBJECTS

Cross-sectional study in a cohort of 78 nonsmoking, predominantly middle-aged, euthyroid subjects (44 men and 34 women, mean age 56 years, TSH between 0.5 mU/l and 4.0 mU/l and FT4 between 11.0 pmol/l and 19.5 pmol/l).

MEASUREMENTS

IMT (mean of three segments in both carotid arteries by ultrasonography), clinical factors, insulin resistance (HOMA(ir)), plasma lipids, C-reactive protein (CRP), serum FT4, TSH and thyroid autoantibodies.

RESULTS

In several multiple linear regression models, age- and sex-adjusted IMT was found to be independently related to either pulse pressure and body mass index (BMI), to high density lipoprotein (HDL) cholesterol or to FT4, but not to TSH, thyroid autoantibodies, HOMA(ir), CRP, non-HDL cholesterol and triglycerides. In a subsequent model which included age, sex, pulse pressure, body mass index (BMI), HDL cholesterol and FT4, IMT was independently and positively related to age (beta = 0.43, P < 0.001), male sex (beta = 0.34, P = 0.014), pulse pressure (beta = 0.29, P = 0.002), BMI (beta = 0.24, P = 0.007) and inversely related to FT4 (beta = -0.19, P = 0.046). IMT was also inversely related to FT4 in a model which included HDL cholesterol, non-HDL cholesterol and triglycerides.

CONCLUSIONS

In euthyroid subjects, IMT is associated with FT(4), after controlling for clinical factors, lipid levels and thyroid autoantibodies. These findings raise the possibility that, even within the euthyroid range, low normal thyroid function may adversely affect cardiovascular risk.

Cardiovascular risk and subclinical hypothyroidism: focus on lipids and new emerging risk factors. What is the evidence?

Controversy remains as to the risk of cardiovascular disease (CVD) associated with subclinical hypothyroidism (SCH), defined as an increased serum thyrotropin (TSH) concentration with normal free thyroxine and triiodothyronine levels. Substantial evidence indicates altered cholesterol and lipoprotein metabolism in SCH when serum TSH is above 10 mU/L. Observed abnormalities include elevated plasma levels of total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C); the altered TC/high-density lipoprotein-cholesterol (HDL-C) and LDL-C/HDL-C ratios suggest a potential accelerated risk for CVD. The influence of SCH on lipids is directly proportional to the degree of TSH elevation and becomes more significant with the progression from SCH to overt disease, thereby accelerating any propensity to atherosclerosis. Although many clinicians may tend to ignore SCH with TSH levels <10, it is apparent that an enhanced CV risk could apply to these individuals, perhaps compounded by insulin resistance and amplified by the copresence of other risk factors such as endothelial dysfunction and elevated C-reactive protein.

Association between oxidative stress and coronary lipid risk factors in hypothyroid women is independent of body mass index

Hypothyroidism enhances the progression of atherogenesis. Furthermore, dyslipidemia, hypertension, and obesity are known risk factors for atherosclerosis. Oxidative stress is implicated in the pathogenesis of cardiovascular diseases. However, there are contradicting reports on the existence of oxidative stress in hypothyroidism. Thus, the aim of the study is to evaluate the presence of oxidative stress in hypothyroidism and, if so, its possible association with various coronary lipid risk factors. The present study was carried out in a group of 27 freshly diagnosed normotensive primary hypothyroid female patients in comparison with healthy subjects. Their body mass index (BMI), serum thyroid profile, lipid profile, glucose, protein carbonylation, thiobarbituric acid reactive substances (TBARS), and blood antioxidant enzyme levels were estimated. The TBARS and protein carbonylation were significantly higher in cases compared with those in controls. Reduced glutathione was lower and glutathione peroxidase was higher in the test group compared with those in controls. Various lipid risk factors for coronary artery disease were significantly higher among the hypothyroid women in comparison with those in controls. The level of TBARS correlated significantly with various lipid risk factors among the hypothyroid women even after correcting the effect of BMI. However, no significant associations were observed between BMI and these risk factors when the effect of TBARS was nullified. In hypothyroidism, the coronary lipid risk factors seem to be more associated with lipid peroxidation than BMI. In conclusion, the present study indicates the presence of oxidative stress in hypothyroid patients and its association with atherogenic dyslipidemia, which is independent of BMI.

The occurrence of hypothyroidism following radioactive iodine treatment of toxic nodular goiter is related to the TSH level

BACKGROUND

Strategies to increase frequency of euthyroidism following radioactive (RAI) treatment of hyperthyroidism are required.

AIMS

To examine the role of TSH in development of hypothyroidism post RAI treatment in patients with Graves' disease (N = 98) or toxic nodular goiter, TNG (N = 88).

DESIGN

This retrospective study examined thyroid status over a mean of 3.7 years post-RAI.

RESULTS

Although RAI dose was significantly higher in TNG group, hypothyroidism occurred more frequently in Graves' disease (71.4 and 22.7%) P < 0.001. The TSH levels at the time of RAI treatment were lower in TNG patients who remained euthyroid, (0.4+/-0.1 vs. 1.2+/-0.5 mU/l, P < 0.0022).

CONCLUSIONS

A higher frequency of euthyroidism occurs in patients with TNG than with Graves' disease following RAI, particularly when suppressed TSH levels were suppressed at time of RAI-treatment.

Hypertension and hypothyroidism: results from an ambulatory blood pressure monitoring study

OBJECTIVE

To examine differences between hypothyroid patients and healthy volunteers in 24-h ambulatory blood pressure parameters.

METHODS

The study population consisted of 100 individuals who were recently diagnosed for hypothyroidism. These patients had never been treated before with antihypertensive treatment or received drugs for hypothyroidism. All participants underwent 24-h ambulatory blood pressure monitoring. The control group consisted of 100 healthy volunteers matched one to one for gender and age with the hypothyroid participants.

RESULTS

Clinic systolic and diastolic blood pressures were significantly higher in patients with hypothyroidism compared with volunteers. The mean 24-h systolic blood pressure and 24-h pulse pressure were significantly higher in patients with hypothyroidism compared with volunteers. The 24-h systolic blood pressure variability was also significantly higher in patients with hypothyroidism. Fasting serum cholesterol tended to be higher in patients with hypothyroidism compared with volunteers but the difference was not statistically significant, while fasting serum triglycerides were significantly higher. Body mass index was also significantly higher in patients with hypothyroidism.

CONCLUSIONS

These findings indicate that hypothyroidism may be an important predictor of higher mean 24-h systolic blood pressure, 24-h pulse pressure and 24-h systolic blood pressure variability, parameters of ambulatory blood pressure monitoring that have been previously associated with higher cardiovascular target organ damage.

Acute myocardial infarction following hormone replacement in hypothyroidism

Patients with hypothyroidism have an increased risk of coronary artery disease because of significant changes in lipid metabolism and arterial hypertension. We report a 67-year-old man who developed acute myocardial infarction following hormone replacement in hypothyroidism in spite of no previous cardiac symptoms and no ischemia in intravenous dipyridamole myocardial perfusion imaging. Careful examination for ischemic heart disease should be performed before hormone replacement in hypothyroidism.

Hypothyroidism as a risk factor for cardiovascular disease

The cardiovascular risk in patients with hypothyroidism is related to an increased risk of functional cardiovascular abnormalities and to an increased risk of atherosclerosis. The pattern of cardiovascular abnormalities is similar in subclinical and overt hypothyroidism, suggesting that a lesser degree of thyroid hormone deficiency may also affect the cardiovascular system. Hypothyroid patients, even those with subclinical hypothyroidism, have impaired endothelial function, normal/depressed systolic function, left ventricular diastolic dysfunction at rest, and systolic and diastolic dysfunction on effort, which may result in poor physical exercise capacity. There is also a tendency to increase diastolic blood pressure as a result of increased systemic vascular resistance. All these abnormalities regress with L-T4 replacement therapy. An increased risk for atherosclerosis is supported by autopsy and epidemiological studies in patients with thyroid hormone deficiency. The "traditional" risk factors are hypertension in conjunction with an atherogenic lipid profile; the latter is more often observed in patients with TSH >10 mU/L. More recently, C-reactive protein, homocysteine, increased arterial stiffness, endothelial dysfunction, and altered coagulation parameters have been recognized as risk factors for atherosclerosis in patients with thyroid hormone deficiency. This constellation of reversible cardiovascular abnormalities in patient with TSH levels <10 mU/L indicate that the benefits of treatment of mild thyroid failure with appropriate doses of L-thyroxine outweigh the risk.

Elevated C-reactive protein and homocysteine values: cardiovascular risk factors in hypothyroidism? A cross-sectional and a double-blind, placebo-controlled trial

Hypothyroidism is associated with premature atherosclerosis and cardiovascular disease. Recently, total homocysteine (tHcy) and C-reactive protein (CRP) emerged as additional cardiovascular risk factors. We first investigated CRP and tHcy in different severities of primary hypothyroidism and in a second study we evaluated the effect of L-thyroxine treatment in patients with subclinical hypothyroidism (SCH) in a double-blind, placebo-controlled trial. One hundred and twenty-four hypothyroid patients (63 with subclinical, 61 with overt hypothyroidism, OH) and 40 euthyroid controls were evaluated. CRP was measured using a latex-based high sensitivity immunoassay; tHcy was determined by a fluorescence polarization immunoassay. tHcy values were significantly elevated in OH (P=0.01). In SCH tHcy levels were not augmented as compared to controls. CRP values were significantly increased in OH (P=0.016) and SCH (P=0.022) as compared to controls. In a univariate analysis tHcy correlated significantly with fT4, vitamin B12, folic acid and creatinine levels. In multiple regression analysis only fT4 (beta=0.33) had a significant effect on tHcy. CRP did not correlate with thyroid hormones. In SCH, L-T4 replacement had no significant effect on either tHcy or CRP levels. This is the first paper to show that CRP values increase with progressive thyroid failure and may count as an additional risk factor for the development of coronary heart disease in hypothyroid patients. In contrast to overt disease, only CRP, but not tHcy values, are affected in SCH, yet without significant improvement after L-thyroxine therapy.

Thyroid function tests, serum lipids and gender interrelations in a middle-aged population

OBJECTIVE

To study the value of screening for thyroid function in a screening program for hyperlipidaemia.

DESIGN

A screening study in primary health care.

SETTING

All individuals in a defined rural area, Söderåkra, Sweden, aged 40-59 years were invited to a screening programme at the local primary health care centre.

PARTICIPANTS

782 individuals were invited for screening. Blood samples were obtained from 88% of the invited males and from 92% of the females.

MAIN OUTCOME MEASURES

Thyroid function tests (thyroid stimulating hormone (TSH) and free T4), serum lipids (total-cholesterol, HDL-cholesterol, LDL-cholesterol and s-triglycerides), b-glucose and body anthropometry (body mass index and waist to hip circumference) were measured.

RESULTS

0.57% of males and 1.13% of females showed evidence of hypothyroidism as defined by a TSH value greater than 3.75 mU/l of those with s-cholesterol concentration above 7 mmol/l. In addition, higher TSH values in females were associated with higher s-cholesterol, s-LDL-cholesterol and s-triglycerides.

CONCLUSION

It seems appropriate to screen for hypothyroidism in females with s-cholesterol above 7.0 mmol/l.

Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study

BACKGROUND

Overt hypothyroidism has been found to be associated with cardiovascular disease. Whether subclinical hypothyroidism and thyroid autoimmunity are also risk factors for cardiovascular disease is controversial.

OBJECTIVE

To investigate whether subclinical hypothyroidism and thyroid autoimmunity are associated with aortic atherosclerosis and myocardial infarction in postmenopausal women.

DESIGN

Population-based cross-sectional study.

SETTING

A district of Rotterdam, The Netherlands.

PARTICIPANTS

Random sample of 1149 women (mean age +/- SD, 69.0 +/- 7.5 years) participating in the Rotterdam Study.

MEASUREMENTS

Data on thyroid status, aortic atherosclerosis, and history of myocardial infarction were obtained at baseline. Subclinical hypothyroidism was defined as an elevated thyroid-stimulating hormone level (>4.0 mU/L) and a normal serum free thyroxine level (11 to 25 pmol/L [0.9 to 1.9 ng/dL]). In tests for antibodies to thyroid peroxidase, a serum level greater than 10 IU/mL was considered a positive result.

RESULTS

Subclinical hypothyroidism was present in 10.8% of participants and was associated with a greater age-adjusted prevalence of aortic atherosclerosis (odds ratio, 1.7 [95% CI, 1.1 to 2.6]) and myocardial infarction (odds ratio, 2.3 [CI, 1.3 to 4.0]). Additional adjustment for body mass index, total and high-density lipoprotein cholesterol level, blood pressure, and smoking status, as well as exclusion of women who took beta-blockers, did not affect these estimates. Associations were slightly stronger in women who had subclinical hypothyroidism and antibodies to thyroid peroxidase (odds ratio for aortic atherosclerosis, 1.9 [CI, 1.1 to 3.6]; odds ratio for myocardial infarction, 3.1 [CI, 1.5 to 6.3]). No association was found between thyroid autoimmunity itself and cardiovascular disease. The population attributable risk percentage for subclinical hypothyroidism associated with myocardial infarction was within the range of that for known major risk factors for cardiovascular disease.

CONCLUSION

Subclinical hypothyroidism is a strong indicator of risk for atherosclerosis and myocardial infarction in elderly women.

Normalization of hyperhomocysteinemia with L-thyroxine in hypothyroidism

BACKGROUND

Hyperhomocysteinemia is an independent risk factor for coronary, peripheral, and cerebrovascular disease. Elevated plasma homocysteine levels were described in a preliminary report on primary hypothyroidism.

OBJECTIVE

To determine whether restoration of euthyroidism by L-thyroxine replacement therapy would reduce or normalize plasma homocysteine levels.

DESIGN

Prospective cohort study.

SETTING

Outpatient endocrinology department of a tertiary center.

PATIENTS

14 patients (10 women and 4 men; 25 to 77 years of age): 4 with newly diagnosed chronic (Hashimoto) hypothyroidism and 10 who had been rendered acutely hypothyroid (thyroid-stimulating hormone level > 25 mU/L) by total thyroidectomy for thyroid carcinoma.

MEASUREMENTS

Total plasma homocysteine levels were measured at baseline and 3 to 9 months later, after euthyroidism had been attained by L-thyroxine replacement therapy.

RESULTS

Median baseline plasma homocysteine levels in both sexes (women, 11.65 micromol/L [range, 7.2 to 26.5 micromol/L]; men, 15.1 micromol/L [range, 14.1 to 16.3 micromol/L]) were higher (P = 0.002) than those in healthy female (n = 35) and male (n = 36) volunteers (women, 7.52 micromol/L [range, 4.3 to 14.0 micromol/L]; men, 8.72 micromol/L [range, 5.94 to 14.98 micromol/L]). Eight patients (57%) had baseline plasma homocysteine levels that exceeded the upper limit of sex-specific reference ranges. Upon attainment of euthyroidism, all patients had a diminution in plasma homocysteine levels. The median overall change of -5.5 micromol/L (range, -15.4 to -1.8 micromol/L) corresponds to a difference of -44% (range, -58% to -13%) (P < 0.001). Homocysteine levels returned to normal in 7 of the 8 patients with elevated pretreatment values.

CONCLUSIONS

Hypothyroidism may be a treatable cause of hyperhomocysteinemia, and elevated plasma homocysteine levels may be an independent risk factor for the accelerated atherosclerosis seen in primary hypothyroidism.

Severe short-term hypothyroidism is not associated with an increased incidence of myocardial ischemia as assessed by thallium-201 stress/rest myocardial scintigraphy

Reversible silent myocardial ischemia associated with treatment of long-standing hypothyroidism has recently been reported using thallium-201 (201Tl) myocardial single photon emission tomography (SPET). The aim of the present study was to evaluate whether patients with short-term hypothyroidism (serum thyrotropin [TSH] levels above 30 mU/L) have an increased risk of silent myocardial ischemia. We studied 20 patients with differentiated thyroid carcinoma that had undergone thyroidectomy and ablative (131)I therapy. None of the patients had a known history of atherosclerotic cardiovascular disease. In the course of a planned follow-up examination, suppressive levothyroxine (LT4) therapy was discontinued 7 weeks prior to scintigraphy and replaced by triiodothyronine (T3) therapy for 4 weeks. No thyroid hormone medication was given during the 3 weeks preceding the diagnostic procedures. All patients were hypothyroid (TSH 87.2 +/- 30.8 mU/L, mean +/- SD) at the time of the examination. 20lTl-SPET was performed immediately after bicycle exercise stress test and again after a delay of 4 hours. In case of abnormal results, (n = 3) the examination was repeated after patients were euthyroid. Two patients showed effects of soft-tissue attenuation (breast attenuation in a female and diaphragmatic attenuation in a male subject). Myocardial ischemia was revealed in 1 patient but was seen in both hypothyroid and euthyroid examinations. The results of the present study show that short-term severe hypothyroidism as encountered in athyreotic patients after cessation of thyroxine medication for several weeks, is not associated with an impairment of myocardial perfusion.

Effect of thyroid hormone replacement on lipoprotein(a), lipids, and apolipoproteins in subjects with hypothyroidism

OBJECTIVE

To study the effect of thyroid hormone replacement on total cholesterol, low-density lipoprotein cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL-C), apolipoprotein A-I and B-100, and lipoprotein(a) [Lp(a)] in subjects with hypothyroidism.

MATERIAL AND METHODS

In 17 patients with clinical primary hypothyroidism, studies were done before and after thyroid hormone replacement therapy. Free thyroxine and thyrotropin were determined by chemiluminescent assay. Total cholesterol and triglycerides were measured by enzymatic methods, and HDL-C was measured after dextran sulfate-MgCl2 precipitation. Apolipoprotein A-I and B-100 were assayed by immunonephelometry. For measurement of Lp(a), we used a sequential sandwich enzyme-linked immunosorbent assay.

RESULTS

After levothyroxine treatment, the mean concentration of thyrotropin decreased from 91.4 to 3.7 microIU/mL, and free thyroxine increased from 0.5 to 1.2 ng/ dL. Total cholesterol, triglycerides, HDL-C, low-density lipoprotein cholesterol, and apolipoprotein A-I and B-100 decreased after thyroid hormone replacement therapy. Lp(a) levels also decreased significantly (P<0.05) after treatment, from a mean of 33.4 to 25.6 mg/dL.

CONCLUSION

Hypothyroidism is associated with an increase in total cholesterol, triglycerides, HDL-C, apolipoprotein A-I and B-100, and Lp(a). A reduction in lipid and lipoprotein levels after thyroid hormone replacement in our study cohort resulted in a less atherogenic profile.

Hypothyroidism reduces HDL binding to rat liver cells

The plasma clearance rate of high density lipoprotein is reduced in the hypothyroid rat. Because the liver is an important site of HDL-cholesterol catabolism, the present study was undertaken to investigate whether thyroid hormone deficiency affects binding of HDL to liver cells. Male Wistar rats were made hypothyroid by feeding propylthiouracil (0.1% w/w). Liver cells were isolated by in situ perfusion of the liver with a buffered collagenase solution. 125I-labelled rat HDL binding to isolated liver cells was carried out at low temperature on ice. For both control and hypothyroid rat liver cells, 125I-HDL binding was significantly inhibited by excess unlabelled rat HDL and also by human HDL3 and human LDL but was unaffected by the addition of 10 mM EDTA. From Scatchard analysis of dose-response studies, hypothyroid cells displayed a lower HDL binding capacity (P less than 0.01) and a higher binding affinity (P less than 0.025) compared to control cells. These results suggest that thyroid hormone affects the expression of the HDL binding site in liver cells which may contribute to the reduced HDL clearance in the hypothyroid animal.

Left ventricular function at rest and during exercise in acute hypothyroidism

The effect of hypothyroidism on left ventricular function at rest and during exercise was studied in nine patients without demonstrable cardiovascular disease who had had total thyroidectomy and ablative radioiodine treatment for thyroid cancer. Radionuclide ventriculography and simultaneous right heart catheterisation were performed while the patients were hypothyroid two weeks after stopping triiodothyronine treatment (to permit routine screening for metastases) and while they were euthyroid on thyroxine replacement treatment. When the patients were hypothyroid, cardiac output, stroke volume, and end diastolic volume at rest were all lower and peripheral resistance was higher than when they were euthyroid. Pulmonary capillary wedge pressure, right atrial pressure, heart rate, left ventricular ejection fraction, and the systolic pressure:volume relation of the left ventricle, which was used as an estimate of the contractile state, were not significantly different when the patients were hypothyroid or euthyroid. During exercise, heart rate, cardiac output, end diastolic volume, and stroke volume were higher when the patients were euthyroid than when they were hypothyroid. Again, pulmonary capillary wedge pressure, ejection fraction, and the systolic pressure:volume relation were similar in both thyroid states. The data suggest that the alterations in cardiac performance seen in short term hypothyroidism are primarily related to changes in loading conditions and exercise heart rate; they do not suggest that acute thyroid hormone deficiency has a major effect on the contractile properties of the myocardium.

LDL/HDL-changes in subclinical hypothyroidism: possible risk factors for coronary heart disease

The aim of the present study was to evaluate the lipid profiles (total cholesterol, triglycerides, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, and the electrophoretic low-density lipoproteins and high-density lipoproteins) in patients with subclinical (n = 52) and overt hypothyroidism (n = 18) in comparison to normal controls (28 and 18, respectively), matched for age, sex and body mass index. Subclinical hypothyroidism was defined as a syndrome with normal free thyroxine and total thyroxine but elevated basal thyrotrophin levels and/or an exaggerated TSH response to oral thyrotrophin releasing hormone. In subclinical hypothyroidism there was an elevated LDL concentration (P less than 0.01), a diminished HDL fraction (P less than 0.05) and a borderline elevated LDL-C (not reaching the limit of significance, P = 0.07). Total cholesterol and triglyceride concentrations remained unaltered. For the whole group of patients and controls significant negative correlations were found between LDL-C and T4 (P less than 0.04), total cholesterol and free thyroxine-index (P less than 0.01); positive correlations could be demonstrated between LDL-C and basal TSH (P less than 0.03), the ratio total cholesterol/HDL-C and basal TSH (P less than 0.03), and triglycerides and basal TSH (P less than 0.01). Our data provide a possible explanation for the higher prevalence of coronary heart disease reported in subclinical hypothyroidism. There may well be a case for the detection and early treatment of such individuals.