Subclinical thyroid disease

A Pediatric Case of Refractory Torsades de Pointes in Autoimmune Hypothyroidism

Hypothyroidism can have a significant impact on cardiac contractility, vascular resistance, blood pressure, and cardiac rhythm. Ventricular arrhythmias induced by hypothyroidism are infrequently reported, especially in pediatric cases. A 15-year-old girl with autoimmune hypothyroidism experienced pulseless ventricular arrhythmias on 2 separate occasions because of nonadherence to levothyroxine medication. Subsequent investigations revealed an SCN5A mutation associated with Brugada syndrome. A loop recorder captured polymorphic ventricular tachycardia (PMVT), specifically Torsades de Pointes during her second event. Both arrhythmias were addressed only after stabilizing her thyroid hormone levels with replacement therapy. Although rare, patients with uncontrolled hypothyroidism may present with ventricular arrhythmias, particularly PMVT. The cornerstone of treatment for hypothyroidism-induced ventricular arrhythmia is thyroid replacement therapy. The identification of an SCN5A mutation unmasked by overt hypothyroidism emphasizes the need for a comprehensive cardiac evaluation in patients with hypothyroidism being assessed for PMVT.

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.

Regulation of nitric oxide production in hypothyroidism

Hypothyroidism is a common endocrine disorder that predominantly occurs in females. It is associated with an increased risk of cardiovascular diseases (CVD), but the molecular mechanism is not known. Disturbance in lipid metabolism, the regulation of oxidative stress, and inflammation characterize the progression of subclinical hypothyroidism. The initiation and progression of endothelial dysfunction also exhibit these changes, which is the initial step in developing CVD. Animal and human studies highlight the critical role of nitric oxide (NO) as a reliable biomarker for cardiovascular risk in subclinical and clinical hypothyroidism. In this review, we summarize the recent literature findings associated with NO production by the thyroid hormones in both physiological and pathophysiological conditions. We also discuss the levothyroxine treatment effect on serum NO levels in hypothyroid patients.

Effect of Thyroxine Therapy on Depressive Symptoms Among Women With Subclinical Hypothyroidism

OBJECTIVE

To estimate the effect of antenatal treatment of subclinical hypothyroidism on maternal depressive symptoms.

METHODS

We conducted an ancillary study to a multicenter trial in women with singleton pregnancies diagnosed with subclinical hypothyroidism randomized to antenatal thyroxine therapy or placebo. Treatment was discontinued at the end of pregnancy. Women with overt thyroid disease, diabetes, autoimmune disease, and those diagnosed with depression were excluded. Participants were assessed for depressive symptoms using the Center for Epidemiological Studies-Depression scale (CES-D) before starting the study drug (between 11 and 20 weeks of gestation), between 32 and 38 weeks of gestation, and at 1 year postpartum. The primary outcome was maternal depressive symptoms score as assessed using the CES-D. Secondary outcome was the percentage of women who scored 16 or higher on the CES-D, as such a score is considered screen-positive for depression.

RESULTS

Two hundred forty-five (36.2% of parent trial) women with subclinical hypothyroidism were allocated to thyroxine (n=124) or placebo (n=121). Median CES-D scores and the proportion of participants with positive scores were similar at baseline between the two groups. Treatment with thyroxine was not associated with differences in CES-D scores (10 [5-15] vs 10 [5-17]; P=.46) or in odds of screening positive in the third trimester compared with placebo, even after adjusting for baseline scores (24.3% vs 30.1%, adjusted odds ratio 0.63, 95% CI 0.31-1.28, P=.20). At 1 year postpartum, CES-D scores were not different (6 [3-11] vs 6 [3-12]; P=.79), nor was the frequency of screen-positive CES-D scores in the treated compared with the placebo group (9.7% vs 15.8%; P=.19). Treatment with thyroxine during pregnancy was also not associated with differences in odds of screening positive at the postpartum visit compared with placebo even after adjusting for baseline scores. Sensitivity analysis including women who were diagnosed with depression by the postpartum visit did not change the results.

CONCLUSIONS

This study did not achieve its planned sample size, thus our conclusions may be limited, but in this cohort of pregnant women with subclinical hypothyroidism, antenatal thyroxine replacement did not improve maternal depressive symptoms.

Serum nitric oxide levels correlate with quality of life questionnaires scores of hypothyroid females

Primary hypothyroidism can affect lipid metabolism, cardiovascular (CV) function, and overall patients' quality of life (QoL). Decrease in serum nitric oxide (NO) levels could promote the atherosclerosis acceleration in hypothyroid patients. Our hypothesis is that serum NO level is altered in hypothyroidism; more specifically, we hypothesize that the early vascular changes that can be observed in hypothyroidism could be due to these alterations and that serum NO levels are associated with lipid levels in female patients diagnosed with subclinical hypothyroidism (SCH) or clinical hypothyroidism (CH). Furthermore, since serum NO level is an early marker of atherosclerosis and related CV disorders, which are commonly present and follow hypothyreosis and greatly contribute to overall QoL, we further hypothesized that NO level would correlate with Thyroid Symptom Questionnaire (TSQ) and General Health Questionnaire 12 (GHQ12) scores in hypothyroid patients. A collaterally of our hypothesis was that levothyroxine (LT4) treatment would affect serum NO levels as well as TSQ and GHQ12 scores. Therefore, we have analyzed lipid profile, the level of NO and QoL scores in female patients diagnosed with SCH and CH in order to determine the correlation between NO and generic and thyroid disease symptoms in treatment naïve SCH and CH patients and after LT4 treatment and laboratory euthyroidism achievement. As a consequence of our hypothesis is that measurement of serum NO level in SCH and CH patients may be an innovative way to improve LT4 treatment efficacy. This assumption could have a practical significance for future investigations regarding the management of hypothyroidism treatment protocols in current guidelines.

A Cross-Sectional Study to Assess the Prevalence of Adult Thyroid Dysfunction Disorders in Jordan

Background: Insufficient production of thyroid hormones results in hypothyroidism, while overproduction results in hyperthyroidism. These are common adult disorders, with hypothyroidism more common in the elderly. Jordan has had past problems with dietary iodine deficiency but there are no published studies assessing the population prevalence of these disorders in the Arab Middle East. Methods: A cross-sectional study was conducted in three representative areas of Jordan. There were 7085 participants with a mean age of 40.8 years. Participants completed a questionnaire and had blood taken for thyroid analysis. Results:Hypothyroidism: The prevalence of any hypothyroidism (already diagnosed and/or identified by blood testing) was 17.2% in females and 9.1% in males. Undiagnosed prevalence was 8% and 6.2% for females and males, respectively. The prevalence of subclinical hypothyroidism, defined as high serum thyrotropin (TSH) and normal serum-free thyroxine (fT4), was 5.98% among females and 4.40% among males. The prevalence of overt hypothyroidism, defined as high TSH and low fT4, was 2.00% among females and 1.80% among males. Only 53.5% (55.3% for females, 42.1% males) of those previously diagnosed with hypothyroidism had TSH levels within the appropriate range. Hyperthyroidism: The prevalence of any hyperthyroidism (already diagnosed and/or identified by blood testing) was 1.8% in females and 2.27% in males. The undiagnosed prevalence was 1.4% and 2.1% for females and males, respectively. The prevalence of subclinical hyperthyroidism (low TSH and normal fT4) was 1.20% and 1.80% among males and females accordingly. The prevalence of overt hyperthyroidism (low TSH and high fT4) was 0.2% among females and 0.3% among males. About 85.7% (83.3% for females, 100% males) of those previously diagnosed with hyperthyroidism had TSH levels within the appropriate range. Conclusions: The results of this study reveal that the total prevalence of thyroid dysfunction among adult females and males in Jordan is very high compared with international statistics, particularly in the rates of undiagnosed cases. This indicates the need for further assessment of the value of screening for adult hypothyroidism in Jordan.

Effects of Shuganjianpihuatanxingqi decoction on mild subclinical hypothyroidism: A SPIRIT compliant randomized controlled trial study protocol

INTRODUCTION

Mild subclinical hypothyroidism (SCH) can cause depression, fatigue, cognitive dysfunction, or other hypothyroid symptoms, and even progress to hypothyroidism. The treatment of mild SCH is controversial. Shuganjianpihuatanxingqi decoction (SD) is a frequently prescribed Chinese herbal medicine in patients with mild SCH. However, scientific evidence is needed to confirm the therapeutic effect of SD.

METHODS AND ANALYSIS

This study is a randomized, double-blind, and controlled clinical trial. A total of 228 participants with the diagnosis of mild SCH will be randomly assigned to the SD or placebo group in a ratio of 1:1. Participants will receive treatment for 12 weeks and undergo 12-month follow-up. The primary outcome measure is the thyroid-stimulating hormone level, and secondary outcomes will be the differences in the results of Thyroid-related Quality of Life Questionnaire, blood lipids, and Traditional Chinese Medicine Symptom Score Scale between baseline and at 12 weeks after intervention.

ETHICS AND DISSEMINATION

The study has been approved by Guang'anmen Hospital of China Academy of Chinese Medical Sciences (no.2018-005-ky-01). The trial results will be published via peer-reviewed journals and the Clinical Research Information Service.

TRIAL REGISTRATION NUMBER

ChiCTR1800015781 (approval date: 20 April 2018).

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.

Study protocol; Thyroid hormone Replacement for Untreated older adults with Subclinical hypothyroidism - a randomised placebo controlled Trial (TRUST)

BACKGROUND

Subclinical hypothyroidism (SCH) is a common condition in elderly people, defined as elevated serum thyroid-stimulating hormone (TSH) with normal circulating free thyroxine (fT4). Evidence is lacking about the effect of thyroid hormone treatment. We describe the protocol of a large randomised controlled trial (RCT) of Levothyroxine treatment for SCH.

METHODS

Participants are community-dwelling subjects aged ≥65 years with SCH, diagnosed by elevated TSH levels (≥4.6 and ≤19.9 mU/L) on a minimum of two measures ≥ three months apart, with fT4 levels within laboratory reference range. The study is a randomised double-blind placebo-controlled parallel group trial, starting with levothyroxine 50 micrograms daily (25 micrograms in subjects <50Kg body weight or known coronary heart disease) with titration of dose in the active treatment group according to TSH level, and a mock titration in the placebo group. The primary outcomes are changes in two domains (hypothyroid symptoms and fatigue / vitality) on the thyroid-related quality of life questionnaire (ThyPRO) at one year. The study has 80% power (at p = 0.025, 2-tailed) to detect a change with levothyroxine treatment of 3.0% on the hypothyroid scale and 4.1% on the fatigue / vitality scale with a total target sample size of 750 patients. Secondary outcomes include general health-related quality of life (EuroQol), fatal and non-fatal cardiovascular events, handgrip strength, executive cognitive function (Letter Digit Coding Test), basic and instrumental activities of daily living, haemoglobin, blood pressure, weight, body mass index and waist circumference. Patients are monitored for specific adverse events of interest including incident atrial fibrillation, heart failure and bone fracture.

DISCUSSION

This large multicentre RCT of levothyroxine treatment of subclinical hypothyroidism is powered to detect clinically relevant change in symptoms / quality of life and is likely to be highly influential in guiding treatment of this common condition.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01660126 ; registered 8th June 2012.

Relationship between thyroid stimulating hormone and night shift work

BACKGROUND

Night shift work has well-known adverse effects on health. However, few studies have investigated the relationship between thyroid diseases and night shift work. This study aimed to examine night shift workers and their changes in thyroid stimulating hormones (TSH) levels over time.

METHODS

Medical check-up data (2011-2015) were obtained from 967 female workers at a university hospital in Incheon, Korea. Data regarding TSH levels were extracted from the records, and 2015 was used as a reference point to determine night shift work status. The relationships between TSH levels and night shift work in each year were analyzed using the general linear model (GLM). The generalized estimating equation (GEE) was used to evaluate the repeated measurements over the 5-year period.

RESULTS

The GEE analysis revealed that from 2011 to 2015, night shift workers had TSH levels that were 0.303 mIU/L higher than the levels of non-night shift workers (95 % CI: 0.087-0.519 mIU/L, p = 0.006) after adjusting for age and department. When we used TSH levels of 4.5 ≥ mIU/L to identify subclinical hypothyroidism, night shift workers exhibited a 1.399 fold higher risk of subclinical hypothyroidism (95 % CI: 1.050-1.863, p = 0.022), compared to their non-night shift counterparts.

CONCLUSIONS

This result of this study suggests that night shift workers may have an increased risk of thyroid diseases, compared to non-night shift workers.

Endothelial dysfunction in patients with subclinical hypothyroidism and the effects of treatment with levothyroxine

Background:

Subclinical hypothyroidism (SHT) may increase the risk of cardiovascular disease. We compared endothelial function between SHT patients and euthyroid individuals, and evaluated the effects of levothyroxine therapy on endothelial function in the patients.

Materials and Methods:

In a quasi-experimental study, flow-mediated dilatation (FMD) and intima-media thickness (IMT) were assessed in SHT patients and healthy controls (n = 25 in each group). Patients then received levothyroxine (50 μg/day) for 2 months, and the FMD and IMT assessments were repeated.

Results:

Patients and controls were similar in IMT (0.56 ± 0.09 vs. 0.58 ± 0.08 mm, P = 0.481), but FMD was lower in patients than in controls (4.95 ± 2.02 vs. 6.50 ± 2.57%, P = 0.011). A significant increase was observed in FMD (4.11 ± 2.37%, P = 0.001), but not in IMT (−0.004 ± 0.020 mm, P = 0.327), after levothyroxine therapy among the patients.

Conclusions:

Patients with SHT have endothelial dysfunction which responds to levothyroxine therapy. Randomized placebo-controlled trials are needed to confirm these findings.

Stress, relationship satisfaction, and health among African American women: Genetic moderation of effects

We examined whether romantic relationship satisfaction would serve as a link between early and later stressors which in turn would influence the thyroid function index (TFI), an indicator of physiological stress response. Using the framework of genetic susceptibility theory combined with hypotheses derived from the vulnerability-stress-adaptation and stress-generation models, we tested whether the hypothesized mediational model would be conditioned by 5-HTTLPR genotype, with greater effects and stronger evidence of mediation among carriers of the "s" allele. In a sample of African American women in romantic relationships (n = 270), we found that 5-HTTLPR moderated each stage of the hypothesized mediational model in a "for better or for worse" manner. That is genetic polymorphisms function to exacerbate not only the detrimental impact of negative environments (i.e., "for worse effects") but also the beneficial impact of positive environments (i.e., "for better effects"). The effect of early stress on relationship satisfaction was greater among carriers of the "short" allele than among those who did not carry the short allele, and was significantly different in both the "for better" and "for worse" direction. Likewise, the effect of relationship satisfaction on later stressors was moderated in a "for better "or "for worse" manner. Finally, impact on physiological stress, indexed using TFI level, indicated that the impact of later stressors on TFI level was greater in the presence of the short allele, and also followed a "for better" or "for worse" pattern. As expected, the proposed mediational model provided a better fit for "s" allele carriers.

Clinical presentation of hyperthyroidism in a large representative sample of outpatients in France: relationships with age, aetiology and hormonal parameters

OBJECTIVE

Signs and symptoms of thyrotoxicosis are not specific, and thyroid function tests are frequently prescribed to recognize such thyroid dysfunction. Ultrasensitive assays of thyroid-stimulating hormone (TSH) allow early diagnosis and identification of mild hyperthyroidism (generally designed as 'subclinical'). The aim of this study was to re-evaluate the clinical picture of thyrotoxicosis in the context of the current large utilization of ultrasensitive TSH assays.

DESIGN

Prospective descriptive cohort.

METHODS

Clinical presentation of 1572 patients with a recent (<3 months) diagnosis of thyrotoxicosis recruited by a large representative sample of 263 French endocrinologists was studied using two questionnaires (one at inclusion and the second after 3 months) concerning symptoms, hormonal evaluation and treatment.

RESULTS

A total of 1240 (78·9%) patients were women, mean age 48 ± 17 years. Subclinical hyperthyroidism (SCHT) was present in 86 patients (10·4%). Symptoms of thyrotoxicosis were in decreasing frequency order: palpitations, weakness, heat-related signs and disturbed sleep. A total of 64·9% of patients had lost weight. Signs and symptoms were more frequent in Graves' disease, in young patients, and were partially related to biochemical severity. Symptoms were less frequent in elderly patients except for cardiac manifestations (atrial fibrillation). Most patients with SCHT had one or several signs or symptoms of thyrotoxicosis.

CONCLUSION

This study confirms that elderly patients have less symptoms of thyrotoxicosis than younger subjects but are at increased risk of cardiac complications. Our results show that most patients with 'subclinical' HT have in fact signs or symptoms of thyrotoxicosis.

Depressive symptoms in patients with subclinical hypothyroidism--the effect of treatment with levothyroxine: a double-blind randomized clinical trial

Despite the increasing evidence for relationships between thyroid dysfunction and neuropsychiatric alterations, the effect of treatment of thyroid disease on various clinical psychiatric outcomes is controversial. The purpose of this study was to investigate the effect of levothyroxine treatment on depressive symptoms in subjects with subclinical hypothyroidism. A randomized double-blind placebo-controlled clinical trial was performed. Sixty subjects (51 females and 9 males) with subclinical hypothyroidism were enrolled. Beck Depression Inventory was completed for all participants at the beginning of the study and 12 weeks after enrollment. The intervention and control groups received levothyroxine and placebo, respectively, for 12 weeks. There were no statistical differences in the total depression score and its subscales between the two groups at the beginning of the study. The Beck Depression Inventory score decreased from 16.79 ± 13.25 to 12.37 ± 10.01 (p value = 0.04) in the intervention group. The change in score was not significant for the control group (13.77 ± 11.71 to 11.86 ± 10.71; p value= 0.16). The affective subscale of Beck Depression Inventory did not change after 12 weeks of treatment with levothyroxine, while somatic subscale remarkably improved in the intervention group (p value = 0.02). This study showed the efficacy of treatment of subclinical hypothyroidism in people with levothyroxine in relation to depressive symptoms.

Well-being and depression in individuals with subclinical hypothyroidism and thyroid autoimmunity - a general population study

BACKGROUND

The association between subclinical hypothyroidism (SCH), with and without raised thyroid peroxidase antibodies (anti-TPO), and well-being or depression is still controversial, in spite of many studies on the topic.

AIMS

In this large general population study of 8214 individuals, we aim to clarify the significance of elevated levels of anti-TPO as a marker of poor well-being and depression in euthyroid individuals and individuals with SCH.

METHODS

In participants from the Danish General Suburban Population Study (GESUS), serum thyroid stimulating hormone (TSH), total triiodothyronine (tT3), free thyroxine (fT4) and anti-TPO was measured. Prevalence of poor well-being and depression was measured using the WHO-5 Well-being questionnaire and WHO MDI [Major (ICD-10) Depression Inventory] questionnaire.

RESULTS

Raw score for well-being or depression overall and stratified for sex was not more significantly different in euthyroid individuals than in individuals with SCH, with or without high anti-TPO, except that euthyroid women with elevated anti-TPO had better well-being (P = 0.03) compared with euthyroid women with anti-TPO within the reference range.

CONCLUSION

Elevated anti-TPO levels cannot be used as a general marker of poor well-being or depression in the general population.

Subclinical hypothyroidism in childhood and adolescense

Subclinical hypothyroidism (SH) is defined as a serum thyroid-stimulating hormone (TSH) level above the reference range with normal serum free thyroxin (sT4) and free triiodothyronine (sT3) levels. The prevalence of SH in children and adolescents is reported between 1.7% and 9.5%. Hashimoto's thyroiditis is the most prevalent cause of SH in children. Although it has been suggested that SH is entirely an asymptomatic laboratory diagnosis, typical hypothyroid symptoms as well have been reported in some patients. Results of the adult studies on SH revealed that SH had unfavorable effects on cardiovascular system (atherosclerosis); metabolic parameters (dyslipidemia, insulin resistance, etc.); neuromuscular system; and cognitive functions in the long term. The number of studies investigating the effect of childhood SH on growth, bone maturation, lipid parameters, carbohydrate metabolism, neuromuscular system, and cognitive and cardiac function is limited. Knowledge about the natural history of SH is unclear even though there are numerous studies upon this subject. In children and adults, treatment of SH with L-T₄ is still a matter of debate, and there is no consensus on this issue yet.

Subclinical Thyroid Disorders: Clinical Significance and When to Treat?

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

Does thyroid function influence fracture risk? Prospective data from the HUNT2 study, Norway

OBJECTIVE

To prospectively study the relation between TSH and risk of hip and forearm fractures.

DESIGN

A population-based cohort study.

METHODS

In a substudy of the second survey of the Nord Trøndelag Health Study, Norway (HUNT2, 1995-97), linked with a hospital-based fracture registry, we investigated the relation between baseline TSH and risk of hip and/or forearm fractures.

POPULATION

A total of 16 610 women and 8595 men aged 40 years or more, without previous self-reported thyroid disease and hip or forearm fractures.

RESULTS

During 12.5 years follow-up, a total of 1870 women and 342 men experienced hip or forearm fractures. Overall, there was no relation between baseline TSH and fracture risk. However, there was weak evidence that women with TSH <0.5 and >3.5 mU/l had a slightly increased risk of hip fractures (hazard ratio (HR) 1.30, 95% CI 0.97-1.94 and HR 1.19, 95% CI 0.93-1.52) compared with the reference group with TSH of 1.5-2.4 mU/l. Supplementary analyses showed higher hip fracture risk in women with TSH >4.0 mU/l and negative thyroid peroxidase antibodies (TPOAb) compared with the reference group (HR 1.75, 95% CI 1.24-2.46).

CONCLUSION

We found no statistically significant relation between baseline TSH and subsequent fracture risk, but the data suggest a weak positive association with hip fracture risk among women with both low and high TSH. The latter association was confined to women with negative TPOAb status.

Current concepts of thyroid function and laboratory evaluation

The role of triodothyronine (T(3) in regulating thyroid function is paramount in that at cellular level it interacts with receptors in the nucleus and thereby modulates gene expression. The multiple steps in the processing of lodide by the thyroid gland is under the influence of the thyroid stimulating hormone (TSH). In terms of laboratory evaluation of thyroid function the primary test is TSH. To discriminate between hypothalamic and pitutary dysfunction, the thyroid releasing hormone (TRH) stimulation test is useful. Currently used 2-site Immunometric procedures that employ mouse monoclonal antibodies can be subject to Interference by heterophlle antibodies in patient's serum. Drugs and other extraneous substances can influence the results obtained in some thyroid function tests. Thyroid dysfunction could also be due to autoimmune disease. The limitations of the usefulness of thyroid function tests in non-thyroidal illness should be kept in perspective. In conclusion, the proper interpretation of results of thyroid function tests depends on the sound understanding of concepts of thyroid function and variables affecting laboratory testing.

Evaluation of the effect of L-thyroxin therapy on endothelial functions in patients with subclinical hypothyroidism

Subclinical hypothyroidism (SH) is characterized by normal serum free T4 (FT4), free T3 (FT3) levels and increased serum thyroid-stimulating hormone (TSH) levels. Endothelial dysfunction, which is an early step of atherosclerosis, has been reported in patients with subclinical hypothyroidism. The aim of this study is to evaluate endothelial functions and the effect of L-thyroxin (L-T4) therapy on endothelial functions in SH. Twenty-seven patients with SH and 22 healthy controls were evaluated in terms of endothelial functions, using brachial artery Doppler ultrasonography. After restorating euthyroidism, measurements were repeated. Baseline and nitroglycerin induced diameter (NID) of brachial artery were similar in patients with SH and the control group. Compared to the control group, the patients with SH showed significantly reduced flow-mediated diameter (FMD). Baseline and NID values were significantly higher after LT4 therapy in SH group. FMD also significantly increased after LT4 therapy. Hypothyroidism accelerates atherogenesis through modification of atherosclerotic risk factors and direct effects on the blood vessels. In this study, we observed marked improvement in endothelial functions after L-T4 therapy in SH patients. We suggest that thyroid hormone replacement therapy may help to prevent atherosclerosis in this group of patients.

Thyroid hormone receptors and reproduction

Thyroid disorders have a great impact on fertility in both sexes. Hyperthyroidism and hypothyroidism cause changes in sex hormone-binding globulin (SHBG), prolactin, gonadotropin-releasing hormone, and sex steroid serum levels. In females, thyroid hormones may also have a direct effect on oocytes, because it is known that specific binding sites for thyroxin are found on mouse and human oocytes. There is also an association between thyroid dysfunction in women and morbidity and outcome in pregnancy. In males, hyperthyroidism causes a reduction in sperm motility. The numbers of morphologically abnormal sperm are increased by hypothyroidism. When euthyroidism is restored, both abnormalities improve or normalize. In women, the alterations in fertility caused by thyroid disorders are more complex. Hyper- and hypothyroidism are the main thyroid diseases that have an adverse effect on female reproduction and cause menstrual disturbances--mainly hypomenorrhea and polymenorrhea in hyperthyroidism, and oligomenorrhea in hypothyroidism. In recent studies, it has become evident that it is not only changes in serum levels of SHBG and sex steroids that are responsible for these disorders, but also alterations in the metabolic pathway. Adequate levels of circulating thyroid hormones are of primary importance for normal reproductive function. This review presents an overview of the impact of thyroid disorders on reproduction.

Hashimoto thyroiditis is more frequent than expected when diagnosed by cytology which uncovers a pre-clinical state

Background

Our Thyroid-Multidisciplinary Clinic is a large referral site for thyroid diseases. Thyroid biopsies are mainly performed for thyroid cancer screening. Yet, Hashimoto thyroiditis (HT) is being too frequently diagnosed. The prevalence of HT is reported as 0.3-1.2% or twice the prevalence of type 1 diabetes. However, the prevalence of HT confirmed by cytology is still uncertain. To evaluate different aspects of thyroid physiopathology including prevalence of Hashimoto's, a database of clinical features, ultrasound images and cytology results of patients referred for FNA of thyroid nodules was prospectively developed.

Methods

We retrospectively studied 811 consecutive patients for whom ultrasound guided thyroid FNA biopsies were performed at our clinic over 2.5 year period (Mar/2006-Sep/2008).

Results

The analysis of our database revealed that from 761 patients, 102 (13.4%) had HT, from whom 56 (7.4%) were euthyroid or had sub-clinical (non-hypothyroid) disease, and 46 (6%) were clinically hypothyroid.

Conclusions

This is the first study to show such a high prevalence of HT diagnosed by ultrasound-guided FNA. More strikingly, the prevalence of euthyroid HT, appears to be >5% similar to that of type 2 diabetes. Based on our results, there might be a need to follow up on cytological Hashimoto's to monitor for thyroid failure, especially in high risk states, like pregnancy. The potential risk for thyroid cancer in patients with biopsy-proven inflammation of thyroid epithelium remains to be established prospectively. However, it may explain the increased risk for thyroid cancer observed in patients with elevated but within normal TSH.

Subclinical thyroid disease

Subclinical thyroid disease, a term applied to patients with no or minimal thyroid-related symptoms with abnormal laboratory values, is diagnosed more frequently with the use of thyroid-stimulating hormone (TSH) screening and newer high-sensitivity assays. These are laboratory diagnoses, with subclinical hypothyroidism defined as an elevated TSH with a normal free thyroxine and triiodothyronine concentration, and subclinical hyperthyroidism as a subnormal TSH with normal free thyroxine and triiodothyronine levels. Although studies defining which patients require treatment are few, decisions should be individualized based upon laboratory values and symptoms. This article reviews the etiologies, diagnoses, treatments and indications, and monitoring of patients with subclinical thyroid disease.

Prevalence and causes of undiagnosed hyperthyroidismin an adult healthy population. The Tromsø study

BACKGROUND

The causes of subclinical hyperthyroidism have only been reported from clinical studies.

AIM

To determine the prevalence and pathological causes of reduced serum TSH levels in subjects recruited from an epidemiological survey.

MATERIAL/SUBJECTS AND METHODS

Serum TSH was measured in 7954 subjects in the 5th Tromsø study. Subjects with serum TSH<0.50 mIU/l, not using T4, without a previous diagnosis of thyroid disease, without serious concomitant disease, and younger than 80 yr, were invited for a re-examination. If low serum TSH was persistent, thyroid scintigraphy was performed.

RESULTS

Among the 4962 subjects that met the inclusion criteria, serum TSH was <0.50 mIU/l in 105 subjects. Twelve subjects had a suppressed serum TSH level (<0.05 mIU/l). Two of these were lost to follow-up, 4 had Graves' disease, 4 had adenoma, and 2 had multinodular goiter. In the 93 subjects with serum TSH 0.05-0.5 mIU/l, 55 were re-examined, of whom 35 had normalized their serum TSH level. In the remaining 20 subjects, 1 had Graves' disease, 6 had adenoma (of which 2 were toxic adenomas), 7 had multinodular goiter, and 6 were considered normal. Among the 521 subjects using T4, 70 (13.4%) had a suppressed serum TSH level.

CONCLUSIONS

Most of the subjects with a suppressed serum TSH level will be on T4 medication. Otherwise, if the suppressed serum TSH level is found by chance, this probably represents a clinically important thyroid pathology. Also, in subjects with a persistently low serum TSH level (0.05-0.5 mIU/l) most will have a pathological thyroid scan.

Longitudinal study of thyroid function in children with mild hyperthyrotropinemia at neonatal screening for congenital hypothyroidism

OBJECTIVE

Long-term outcome of thyroid function in children with very short-lasting neonatal hyperthyrotropinemia ("false positive" at neonatal screening) was studied in an observational, prospective study. Thyroid function and morphology were evaluated in 44 "false positive" children up to advanced childhood (8.0 +/- 0.7 yr of age). In these children a high prevalence (50%) of subclinical hypothyroidism in early childhood (2.8 +/- 0.5 yr) had already been described.

RESULTS

At an average of 5.3 yr, subclinical hypothyroidism persisted in 19 of 44 (43.2%) children and, more specifically, in two of three of those who had increased TSH in early childhood. Euthyroidism was present in all cases that were euthyroid in early childhood, although they had TSH and free T(3) values significantly higher than control children with a normal TSH at birth (TSH = 2.6 +/- 0.7 vs. 1.5 +/- 0.6 mU/liter, P < 0.001; free T(3) = 4.9 +/- 0.8 vs. 3.9 +/- 0.9 pmol/liter, P < 0.01). Thyroid morphology alterations were frequent in the group of children with subclinical hypothyroidism. At an average of 8.0 yr, subclinical hypothyroidism persisted in 14 of 44 (31.8%) children. In all other children, TSH and thyroid hormones were confirmed within the normal range.

CONCLUSIONS

This prospective longitudinal study confirms that newborns "false positive" at neonatal screening have a high risk to develop persistent subclinical hypothyroidism. The prevalence of hypothyroidism decreases with increasing age, but it is still high (>30%) in late childhood. Even those "false positive" children that maintain euthyroidism in late childhood have an average TSH value that, although within the normal range, is higher than in normal controls, a possible marker of minor congenital thyroid function abnormalities.

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.

Subclinical hypothyroidism: the state of the art

Subclinical hypothyroidism (SH) is a common clinical problem, particularly in adulthood and the elderly. Its prevalence is conditioned by several etiological and risk factors. The highest age- and sex-specific rates are in women over 60. SH may be associated with manifestations of mild thyroid failure, which may reverse under levothyroxine (L-T4) therapy. The risk of progression to overt hypothyroidism is distinctly higher in cases with underlying thyroid disease. A population routine screening is not generally recommended, but screening is encouraged in high-risk groups. L-T4 therapy may be indicated in subjects with TSH levels which are repeatedly and consistently elevated (>10 microIU/ml) and may be considered in those with TSH ranging between 4.5-5.5 and 10 microIU/ml, particularly if anti-thyroid antibodies are positive and/or hypothyroid symptoms are present. Treatment should be based, at least initially, on L-T4 low doses.

Coronary flow reserve after L-thyroxine therapy in Hashimoto's thyroiditis patients with subclinical and overt hypothyroidism

BACKGROUND/AIMS

Overt and subclinical hypothyroidism are reported to be associated with increased cardiovascular disease risk. We have used coronary flow reserve (CFR) measurement by trans-thoracic Doppler echocardiography (TTDE) to determine coronary microvascular function in Hashimoto's thyroiditis patients with overt and subclinical hypothyroidism and to evaluate effects of L-thyroxine replacement on coronary endothelial function.

METHODS

In total, 10 overt hypothyroid patients, 10 subclinical hypothyroid patients, and 10 controls were enrolled. FT4, TSH, anti-thyroid antibodies, lipid profile, insulin, glucose, HOMA-IR, physical parameters, and CFR measured by TTDE were recorded before and after 6 months of L: -thyroxine replacement in all groups.

RESULTS

CFR values of all hypothyroid patients at baseline were significantly lower than those in controls. After L: -thyroxine, CFR increased significantly in overt and subclinical hypothyroidism with respect to the baseline measurements (P < 0.05). When baseline and second measurements were evaluated collectively for patients and controls, CFR was positively correlated with FT4 levels (r = 0.31, P = 0.01) and negatively correlated with TSH and HOMA-IR (r = -0.38, P = 0.002 and r = -0.42, P < 0.001, respectively).

CONCLUSION

Subclinical as well as overt hypothyroid patients have impaired coronary microvascular function which improved after L: -thyroxine therapy. Treatment of Hashimoto's thyroiditis patients with subclinical hypothyroidism should be considered to improve cardiovascular disease risk.

Subclinical hypothyroidism: psychiatric disorders and symptoms

OBJECTIVE: To evaluate the prevalence of psychiatric disorders and symptoms in patients with subclinical hypothyroidism. METHOD: Ninety-four outpatients with at least two elevated serum thyrotrophin levels (> 4 µU/ml) and normal FT4, and 43 euthyroid outpatients, both groups from HUCFF-UFRJ, were evaluated. Psychiatric diagnosis was based on the Structured Clinical Interview Diagnostic for the DSM-IV axis I (SCID-I/DSM-IV), the psychopathological symptoms on Hamilton anxiety and depression scales, and the Beck Inventory. RESULTS: Our data showed an increased prevalence of psychiatric disorders in the subclinical hypothyroidism patients when compared to the euthyroid group (45.7% vs 25.6%; p = 0.025), mood disorders being the most frequent. The prevalence of depressive symptoms based on Beck's Scale among subclinical hypothyroidism patients was about 2.3 times higher than among euthyroid ones (45.6% vs 20.9%, p = 0.006). Anxiety symptoms were also more frequent among subclinical hypothyroidism patients (87.0% vs 60.5%, p < 0.001), mainly clinical anxiety (44.6% vs 23.3%; p = 0.001). CONCLUSION: Our results showed a significant association of subclinical hypothyroidism with psychiatric disorders and an increased frequency of subsyndromic depression and anxiety symptoms in subclinical hypothyroidism in relation to the euthyroid group.

Prevalence of subclinical thyroid dysfunction and its relation to socioeconomic deprivation in the elderly: a community-based cross-sectional survey

CONTEXT

Population-based screening has been advocated for subclinical thyroid dysfunction in the elderly because the disorder is perceived to be common, and health benefits may be accrued by detection and treatment.

OBJECTIVE

The objective of the study was to determine the prevalence of subclinical thyroid dysfunction and unidentified overt thyroid dysfunction in an elderly population.

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional survey of a community sample of participants aged 65 yr and older registered with 20 family practices in the United Kingdom.

EXCLUSIONS

Exclusions included current therapy for thyroid disease, thyroid surgery, or treatment within 12 months.

OUTCOME MEASURE

Tests of thyroid function (TSH concentration and free T4 concentration in all, with measurement of free T3 in those with low TSH) were conducted. EXPLANATORY VARIABLES: These included all current medical diagnoses and drug therapies, age, gender, and socioeconomic deprivation (Index of Multiple Deprivation, 2004).

ANALYSIS

Standardized prevalence rates were analyzed. Logistic regression modeling was used to determine factors associated with the presence of subclinical thyroid dysfunction.

RESULTS

A total of 5960 attended for screening. Using biochemical definitions, 94.2% [95% confidence interval (CI) 93.8-94.6%] were euthyroid. Unidentified overt hyper- and hypothyroidism were uncommon (0.3, 0.4%, respectively). Subclinical hyperthyroidism and hypothyroidism were identified with similar frequency (2.1%, 95% CI 1.8-2.3%; 2.9%, 95% CI 2.6-3.1%, respectively). Subclinical thyroid dysfunction was more common in females (P < 0.001) and with increasing age (P < 0.001). After allowing for comorbidities, concurrent drug therapies, age, and gender, an association between subclinical hyperthyroidism and a composite measure of socioeconomic deprivation remained.

CONCLUSIONS

Undiagnosed overt thyroid dysfunction is uncommon. The prevalence of subclinical thyroid dysfunction is 5%. We have, for the first time, identified an independent association between the prevalence of subclinical thyroid dysfunction and deprivation that cannot be explained solely by the greater burden of chronic disease and/or consequent drug therapies in the deprived population.

Low-grade systemic inflammation causes endothelial dysfunction in patients with Hashimoto's thyroiditis

OBJECTIVE

The objective of this study was to assess whether low-grade systemic inflammation might contribute to the pathogenesis of endothelial dysfunction in patients with subclinical hypothyroidism (sHT) and autoimmune thyroiditis.

BACKGROUND

sHT patients are characterized by peripheral endothelial dysfunction and low-grade inflammation.

METHODS

In 53 sHT and 45 healthy subjects, we studied the forearm blood flow (strain-gauge plethysmography) response to intrabrachial acetylcholine (Ach) (0.15-15 microg/min.dl) with and without local vascular COX inhibition by intrabrachial indomethacin (50 microg/min.dl) or nitric oxide synthase blockade by N-mono methyl arginine (L-NMMA) (100 microg/min.dl) or the antioxidant vitamin C (8 mg/min.dl). The protocol was repeated 2 h after systemic nonselective COX inhibition (100 mg indomethacin) or selective COX-2 blockade (200 mg celecoxib) oral administrations.

RESULTS

sHT patients showed higher C-reactive protein and IL-6 values. In controls, vasodilation to Ach was blunted by L-NMMA and unchanged by vitamin C. In contrast, in sHT, the response to Ach, reduced in comparison with controls, was resistant to L-NMMA and normalized by vitamin C. In these patients, systemic but not local indomethacin normalized vasodilation to Ach and the inhibition of L-NMMA on Ach. Similar results were obtained with celecoxib. When retested after indomethacin administration, vitamin C no longer succeeded in improving vasodilation to Ach in sHT patients. Response to sodium nitroprusside was unchanged by indomethacin or celecoxib.

CONCLUSIONS

In sHT patients, low-grade chronic inflammation causes endothelial dysfunction and impaired nitric oxide availability by a COX-2-dependent pathway leading to increased production of oxidative stress.

Hormonal disturbances associated with obesity in dogs

Obesity is associated with multiple endocrine alterations and changes in the concentration of circulating hormones. However, few studies have explored such alterations in dogs with naturally acquired excess weight. In the present study, we investigated the effect of naturally acquired obesity on cortisol, insulin-like growth factor (IGF)-1 and prolactin secretion in dogs. Thirty-one overweight dogs were enrolled in the trial. Blood samples were collected before and after adrenocorticotrophic hormone (ACTH) injection. Free thyroxine (fT4), cortisol, thyroid-stimulating hormone (TSH), IGF-1, prolactin and fructosamine were assayed. Body weight excess increased significantly with age and neutered dogs were more obese than entire ones. The ACTH stimulation test was within the normal range for 26 of 31 dogs. Prolactinaemia was increased in seven dogs and IGF-1 in six dogs. Twenty dogs had a fructosamine concentration >340 microm. Interestingly, 18 of 31 dogs showed disturbances of thyroid function based on high TSH and/or low fT4 baseline concentration, with 11 dogs showing both. According to these parameters only six of 31 dogs were free of hormonal disturbances. These results revealed the high incidence of such disturbances, especially thyroid dysfunction, in obese, but otherwise apparently healthy dogs. They demonstrate the importance of examining endocrine function during the initial evaluation of obese dogs to avoid failure of any nutritional treatment.

Subclinical hypothyroidism is associated with early insulin resistance in Kuwaiti women

Subclinical hypothyroidism (SH), defined as an asymptomatic state characterized by normal serum concentrations of free thyroxine and elevated serum concentrations of TSH. The aim of this study is to investigate the complex interplay between insulin resistance and low grade chronic inflammation in Kuwaiti women with subclinical hypothyroidism. Thirty four women with subclinical hypothyroidism (SH) and 20 healthy women as controls matched to the patient group for sex, age and body mass index (BMI), were enrolled in this prospective study. TSH, FT4, C reactive protein, glucose, insulin, Homeostasis Model assessment (HOMA), total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) were estimated. Total cholesterol and LDL-C were significantly higher in patients with SCH as compared with control subjects, however triglyceride and HDL-C were not statistically different. CRP was not statistically different between the SCH patients and control group (3.64 +/- 0.94 Vs 3.18 +/- 0.71 P>0.05). Insulin levels were significantly higher in the SCH group comparable to the control (12.5 +/- 2.67 Vs 10.80 +/- 2.01 p<0.05), however HOMA-IR was not statistically different (2.85 +/- 0.64 Vs 2.54 +/- 0.64 P>0.05). Patients with subclinical hypothyroidism exhibited elevated atherogenic parameters (hyperinsulinemia, total cholesterol, LDL-C). Therefore screening and treatment for subclinical hypothyroidism may be warranted due to its adverse effects on lipid metabolism.

Thyroid hormone and heart failure

Thyroid hormone metabolic disarray has been identified as a risk factor for the progression of heart disease and the development of heart failure (HF). Both hyper- and hypothyroidism have been associated with a failing myocardium. Poor cardiac contractility and low cardiac output due to hyperthyroidism is a rare occurrence and is mostly seen in patients with preexisting heart disease. Referred to as a "rate related" phenomenon, hyperthyroid-induced sustained sinus tachycardia or atrial fibrillation may further reduce ventricular contractility. Increasingly, the hypothyroid state, and in particular a low triiodothyronine level, has been associated with a reduced cardiac performance and poor prognosis in HF, even in the presence of normal thyroid-stimulating hormone levels. Low thyroid hormone levels alter cardiac gene expression and increase systemic vascular resistance, both resulting in a reduction of cardiac contractility and cardiac output. This review summarizes current data on thyroid dysfunction and HF as well as the emerging implications of the "low triiodothyronine state."

Effect of L-thyroxine treatment on left ventricular function in subclinical hypothyroidism

Aim of this study was to investigate the effects of thyroxine treatment on myocardial regional left ventricular (LV) systolic and diastolic function in patients with subclinical hypothyroidism (SH) by tissue Doppler imaging (TDI). Forty-two patients (29 women and 13 men; mean age 52.2+/-15.1 years) with SH, as judged by elevated serum thyroid-stimulating hormone (TSH) levels (>3.6 mIU/l; range, 3.8-12.0) and free thyroid hormones (FT4 and FT3) within the normal range, and 30 euthyroid volunteers (21 women and nine men; mean age 50.4+/-17.1 years) underwent standard echocardiography and TDI-derived early (Em) and late (Am) diastolic velocities, systolic (Sm) velocity, and isovolumetric relaxation time (IVRTm). Patients were randomly assigned to receive or not L-thyroxine replacement therapy. All patients returned after 6 months to repeat thyroid function tests and the evaluation of all parameters. No significant differences were seen in the Sm peak between SH and control groups. Respect to controls, SH patients exhibited a lower Em, a higher Am, and, subsequently, a reduced Em/Am ratio of both lateral wall (LW) and interventricular septum (IVS) (P<0.001 for both). The IVRTm was distinctly longer in SH patients, as compared to controls (P<0.001). At 6 months, L-thyroxine-treated patients showed a significant increase of Em (P<0.01) and a subsequent increase of the Em/Am ratio (P<0.01), whereas IVRTm significantly reduced (P<0.05). No significant change in any of these parameters was observed in the untreated group. Our data suggest that SH is associated with a subtle, reversible impairment of myocardial function. TDI analysis detects and extends these functional defects by displaying alterations in regional myocardial function. L-T4 replacement therapy should be advised for these patients with the aim to correct preclinical cardiac dysfunction and prevent the development of clinically significant myocardial dysfunction.

Thyroid function during B-vitamin supplementation of patients on antiepileptic drugs

OBJECTIVES

Patients on antiepileptic drugs (AEDs) may have low serum concentrations of thyroxine, with or without a compensatory increment in thyroid-stimulating hormone (TSH). Furthermore, patients on AEDs often have hyperhomocysteinemia and low concentrations of vitamins B(6), B(2) and folate. Previously, an inverse relationship between thyroxine and homocysteine concentrations has been observed. In animals, deficiency of vitamin B(6) has been found to impair the hypophyseal release of TRH. We have studied the effect of B-vitamin supplements on thyroid function in patients on AEDs.

DESIGN AND METHODS

Thirty-two patients on AEDs were identified with hyperhomocysteinemia and low folate, B(6) and B(2). They were supplemented with pyridoxine, riboflavin and folic acid for 30 days.

RESULTS

At baseline, the patients had low serum concentrations of free thyroxin and slightly elevated TSH. On day 30 of the B-vitamin supplements, homocysteine had decreased, however, the thyroid parameters remained unchanged.

CONCLUSIONS

Hyperhomocysteinemic patients on AEDs have indications of hypothyroidism, however, supplementation with B-vitamins does not improve their thyroid function.

Does Treating Subclinical Hypothyroidism Improve Markers of Cardiovascular Risk?

Subclinical hypothyroidism is defined as an elevated serum thyroid-stimulating hormone (TSH) level in the face of normal free thyroid hormone values. The overall prevalence of subclinical hypothyroidism is 4-10% in the general population and up to 20% in women aged >60 years. The potential benefits and risks of therapy for subclinical hypothyroidism have been debated for 2 decades, and a consensus is still lacking. Besides avoiding the progression to overt hypothyroidism, the decision to treat patients with subclinical hypothyroidism relies mainly on the risk of metabolic and cardiovascular alterations. Subclinical hypothyroidism causes changes in cardiovascular function similar to, but less marked than, those occurring in patients with overt hypothyroidism. Diastolic dysfunction both at rest and upon effort is the most consistent cardiac abnormality in patients with subclinical hypothyroidism, and also in those with slightly elevated TSH levels (>6 mIU/L). Moreover, mild thyroid failure may increase diastolic blood pressure as a result of increased systemic vascular resistance. Restoration of euthyroidism by levothyroxine replacement is generally able to improve all these abnormalities. Early clinical and autopsy studies had suggested an association between subclinical hypothyroidism and coronary heart disease, which has been subsequently confirmed by some, but not all, large cross-sectional and prospective studies. Altered coagulation parameters, elevated lipoprotein (a) levels, and low-grade chronic inflammation are regarded to coalesce with the hypercholesterolemia of untreated patients with subclinical hypothyroidism to enhance the ischemic cardiovascular risk. Although a consensus is still lacking, the strongest evidence for a beneficial effect of levothyroxine replacement on markers of cardiovascular risk is the substantial demonstration that restoration of euthyroidism can lower both total and low-density lipoprotein-cholesterol levels in most patients with subclinical hypothyroidism. However, the actual effectiveness of thyroid hormone substitution in reducing the risk of cardiovascular events remains to be elucidated. In conclusion, the multiplicity and the possible reversibility of subclinical hypothyroidism-associated cardiovascular abnormalities suggest that the decision to treat a patient should depend on the presence of risk factors, rather than on a TSH threshold. On the other hand, levothyroxine replacement therapy can always be discontinued if there is no apparent benefit. Levothyroxine replacement therapy is usually safe providing that excessive administration is avoided by monitoring serum TSH levels. However, the possibility that restoring euthyroidism may be harmful in the oldest of the elderly population of hypothyroid patients has been recently raised, and should be taken into account in making the decision to treat patients with subclinical hypothyroidism who are aged >85 years.

The effects of thyroxine replacement on the levels of serum asymmetric dimethylarginine (ADMA) and other biochemical cardiovascular risk markers in patients with subclinical hypothyroidism

BACKGROUND

The relationship between subclinical hypothyroidism (SH) and cardiovascular disease (CVD) is still under debate. The purpose of the present study was to evaluate plasma total homocysteine (tHcy), high sensitive C-reactive protein (hsCRP), small dense low-density lipoprotein (sdLDL), L-arginine and asymmetric dimethylarginine (ADMA) concentrations and their relationship to nitric oxide (NO) production, measured as plasma nitrite-plus-nitrate (NO(x)) concentration, in patients with SH before and after thyroxine replacement therapy and compared with control group values.

DESIGN

Eighty-four women with SH and 33 healthy women as controls matched to the patient group for sex, age and body mass index (BMI), were enrolled in this study. Lipoprotein profile, tHcy, hsCRP, sdLDL, ADMA, L-arginine and NO(x) were measured in pre- and post-treatment blood samples.

RESULTS

The pretreatment total cholesterol (TC), LDL-C, hsCRP, ADMA and L-arginine levels were significantly higher and NO(x) levels were lower than in the control group. After treatment, hsCRP, ADMA and L-arginine levels were significantly reduced and sdLDL and NO(x) levels were significantly increased.

CONCLUSION

The present study demonstrated an elevation of hsCRP and ADMA plasma levels of patients with SH associated with a reduction in NO production, which may contribute to some cardiovascular alterations. The elevated ADMA and hsCRP levels were reduced after thyroxine replacement. Also the sdLDL levels of SH patients were found to be lower than the control group values whereas TC and LDL were elevated. Even though we found an elevation in sdLDL levels after treatment, those values were still not higher than in the control group.

Exogenous subclinical hyperthyroidism during adolescence: effect on peak bone mass

BACKGROUND

Chronic subclinical hyperthyroidism induced by suppressive doses of L-thyroxine (L-T4) therapy, so-called exogenous subclinical hyperthyroidism, may cause diminished bone mass in postmenopausal women. The effect of subclinical hyperthyroidism during childhood and adolescence on peak bone mass, however, has not been evaluated.

OBJECTIVE

To determine whether exogenous subclinical hyperthyroidism during adolescence, the period of critical bone mass acquisition, would reduce peak bone mass.

PATIENTS AND METHODS

Eighteen female adolescents and young adults with Hashimoto's thyroiditis and euthyroid goiter (aged 22.4 +/- 4.4 years) who had been treated with suppressive doses of L-T4, 127.5 +/- 23.7 microg/day, during adolescence (age at onset of subclinical hyperthyroidism, 14.2 +/- 1.5 years) for 6.3 +/- 3.4 years were enrolled in the study. Twenty-nine healthy female volunteers matched for age, weight, height and body mass index served as the controls. Bone mineral density (BMD) was measured by dual energy X-ray absorptiometry.

RESULTS

BMD of the lumbar spine, radius, Ward's triangle and total body were comparable in the two groups. In contrast, BMD of the femoral neck, trochanter and shaft of patients was slightly higher than those of controls. There were no correlations between BMD values and clinical parameters.

CONCLUSION

Exogenous subclinical hyperthyroidism during adolescence has no demonstrable detrimental effect on peak bone mass attainment.

A clinical and therapeutic approach to thyrotoxicosis with thyroid-stimulating hormone suppression only

Subclinical hyperthyroidism is defined as normal serum free thyroxine (T4) and triiodothyronine (T3) concentrations and persistently suppressed thyroid stimulating hormone (TSH) concentrations. The most common cause of subclinical hyperthyroidism is the use of suppressive doses of L-thyroxine for treatment of hypothyroidism or, less commonly, diffuse nontoxic goiter or thyroid carcinoma (exogenous subclinical hyperthyroidism). Endogenous subclinical hyperthyroidism may be caused by a variety of thyroid disorders that result in overproduction and release of thyroid hormones from the gland with normal/high 24-hour thyroid radioiodine uptake or by inflammation in the thyroid resulting in release of excess thyroid hormones and low 24-hour thyroid radioiodine uptake. Several groups have investigated whether persistent endogenous or exogenous subclinical hyperthyroidism, like overt hyperthyroidism, causes symptoms, adverse effects on the cardiovascular and the skeletal systems, and increased mortality, whether endogenous subclinical hyperthyroidism evolves to overt thyrotoxicosis, and whether or not it should be treated. The present report reviews the most important and recent studies of subclinical hyperthyroidism and attempts to draw conclusions based upon the literature and the authors' experience.

Does subclinical hypothyroidism affect cardiac pump performance? Evidence from a magnetic resonance imaging study

OBJECTIVES

We sought to assess the effects of subclinical hypothyroidism (SHT) on the cardiac volumes and function.

BACKGROUND

The cardiovascular system is one of the principal targets of thyroid hormones. Subclinical hypothyroidism is a common disorder that may represent "early" thyroid failure.

METHODS

Thyroid profile was evaluated in 30 females with SHT and 20 matched control subjects. Left ventricular end-diastolic volume (EDV) and end-systolic volume (ESV), stroke volume (SV), cardiac index (CI), and systemic vascular resistance (SVR) were calculated by cardiac magnetic resonance (CMR). Regional greatest systolic lengthening (E1) and greatest systolic shortening (E2) were calculated by tagging CMR.

RESULTS

EDV was lower in SHT than in controls (64.3 +/- 8.7 ml/m(2) vs. 81.4 +/- 11.3 ml/m(2), p < 0.001), as well as SV [corrected] (38.9 +/- 7.5 ml/m(2) vs. 52.5 +/- 6.1 ml/m(2), p < 0.001) and CI (2.6 +/- 0.5 l/[min.m(2)] vs. 3.7 +/- 0.4 l/[min.m(2)], p < 0.001). SVR [corrected] was higher in SHT (12.5 +/- 2.5 mm Hg.min/[l.m(2)] vs. 8.6 +/- 1.1 mm Hg.min/[l.m(2)], p = 0.003). The E1 was higher in controls than in SHT at the basal (p = 0.007), equatorial (p = 0.05), and apical (p = 0.008) levels, as well as E2 at the equatorial (p = 0.001) and apical (p = 0.001) levels. All parameters normalized after replacement therapy. A negative correlation between TSH and EDV (p < 0.001), SV (p < 0.001), CI (p < 0.001), and E1 at the apical level (p < 0.001) and a positive correlation between TSH and SVR (p < 0.001) and E2 at the apical level (p < 0.001) were found.

CONCLUSIONS

Subclinical hypothyroidism significantly decreased cardiac preload, whereas it increased afterload with a consequent reduction in SV and cardiac output. Replacement therapy fully normalized the hemodynamic alterations.

Simple electrocardiographic markers for the prediction of paroxysmal atrial fibrillation in hyperthyroidism

BACKGROUND

Hyperthyroidism is a major cause of paroxysmal atrial fibrillation (AF). The purpose of this study was to evaluate the predictors of AF in the patients with clinical and subclinical hyperthyroidism.

METHODS AND RESULTS

The study population consisted of four groups: group I (57 euthyroid healthy persons), group II (33 patients with subclinical hyperthyroidism), group III (69 patients with overt hyperthyroidism) and group IV (31 patients with overt hyperthyroidism and documented paroxysmal AF). The maximum P wave duration (P maximum) in group IV (114 +/- 8 ms) was significantly higher than group I (102 +/- 7 ms, p < 0.001), group II (106 +/- 7 ms, p < 0.001) and group III (108 +/- 9 ms, p0.005). The P wave dispersion (PWD) was measured as 46 +/- 9 ms in group IV and this was significantly higher than group I (29 +/- 8 ms, p < 0.001), group II (36 +/- 9 ms, p < 0.001) and grup III (38 +/- 8 ms, p = 0.001). The P maximum and PWD were higher in the patients with subclinical hyperthyroidism compared to healthy individuals. Univariate regression analysis revealed that age, P maximum and PWD, multivariate analysis showed that P maximum and PWD were significant predictors of paroxysmal AF. A PWD value of 37.5 ms separated group IV from others with a sensitivity of 90%, specificity of 85%, and positive predictive accuracy of 77%.

CONCLUSION

Simply measuring P maximum and PWD values, we could identify the patients with high risk for the development of AF and these simple ECG parameters may help in clinical judgement to determine the requirement for treatment in the patients with subclinical hyperthyroidism.

Subclinical hyperthyroidism: to treat or not to treat?

Subclinical hyperthyroidism may be defined as the presence of free thyroxine and tri-iodothyronine levels within the reference range and a reduced serum thyroid stimulating hormone (TSH) level. In this review the prevalence of low TSH in the population and health consequences of subclinical hyperthyroidism, for example, effects on heart and bone mass, are discussed. Guidelines for treatment are given, based on expert opinion.

Subclinical hypothyroidism is associated with a low-grade inflammation, increased triglyceride levels and predicts cardiovascular disease in males below 50 years

OBJECTIVE

Mild thyroid failure is associated with an increased risk for development of atherosclerosis, but whether subclinical hypothyroidism is related to risk for cardiovascular disease is controversial. The purpose of the present study was to examine a possible association between subclinical hypothyroidism and cardiovascular disease.

DESIGN

Cross-sectional study of a general population.

PATIENTS

Twelve hundred and twelve subjects, men and women, between 20 and 69 years old without thyroid disease not treated with drugs interfering with thyroid function or analysis of TSH were included.

MEASUREMENTS

Clinical signs of cardiovascular disease based on a questionnaire and medical records and laboratory analysis of lipids, atherothrombotic risk markers, C-reactive protein and TSH.

RESULTS

The main findings were a high incidence of subclinical hypothyroidism (19.7%) in a general population. Subclinical hypothyroidism was associated with higher concentrations of triglycerides and C-reactive protein. Below 50 years of age cardiovascular disease was more frequent in males with subclinical hypothyroidism compared to euthyroid males. Subclinical hypothyroidism was a predictor of cardiovascular disease in males below 50 years with an odds ratio of 3.4 (95% confidence interval 1.6-6.8) for developing cardiovascular disease compared to euthyroid age-matched males.

CONCLUSION

Our study demonstrates that patients with subclinical hypothyroidism have increased levels of triglycerides and signs of low-grade inflammation (raised C-reactive protein levels) and that subclinical hypothyroidism might be a risk factor for development of cardiovascular disease in younger males.