Thyroxine replacement therapy and circulating lipid concentrations

Individualized Therapy for Hypothyroidism: Is T4 Enough for Everyone?

CONTEXT

It is well recognized that some hypothyroid patients on levothyroxine (LT4) remain symptomatic, but why patients are susceptible to this condition, why symptoms persist, and what is the role of combination therapy with LT4 and liothyronine (LT3), are questions that remain unclear. Here we explore evidence of abnormal thyroid hormone (TH) metabolism in LT4-treated patients, and offer a rationale for why some patients perceive LT4 therapy as a failure.

EVIDENCE ACQUISITION

This review is based on a collection of primary and review literature gathered from a PubMed search of "hypothyroidism," "levothyroxine," "liothyronine," and "desiccated thyroid extract," among other keywords. PubMed searches were supplemented by Google Scholar and the authors' prior knowledge of the subject.

EVIDENCE SYNTHESIS

In most LT4-treated patients, normalization of serum thyrotropin levels results in decreased serum T3/T4 ratio, with relatively lower serum T3 levels; in at least 15% of the cases, serum T3 levels are below normal. These changes can lead to a reduction in TH action, which would explain the slower rate of metabolism and elevated serum cholesterol levels. A small percentage of patients might also experience persistent symptoms of hypothyroidism, with impaired cognition and tiredness. We propose that such patients carry a key clinical factor, for example, specific genetic and/or immunologic makeup, that is well compensated while the thyroid function is normal but might become apparent when compounded with relatively lower serum T3 levels.

CONCLUSIONS

After excluding other explanations, physicians should openly discuss and consider therapy with LT4 and LT3 with those hypothyroid patients who have persistent symptoms or metabolic abnormalities despite normalization of serum thyrotropin level. New clinical trials focused on symptomatic patients, genetic makeup, and comorbidities, with the statistical power to identify differences between monotherapy and combination therapy, are needed.

The Swinging Pendulum in Treatment for Hypothyroidism: From (and Toward?) Combination Therapy

Thyroid hormone replacement for hypothyroidism can be achieved via several approaches utilizing different preparations of thyroid hormones, T3, and/or T4. "Combination therapy" involves administration of both T3 and T4, and was technically the first treatment for hypothyroidism. It was lauded as a cure for the morbidity and mortality associated with myxedema, the most severe presentation of overt hypothyroidism. In the late nineteenth and the early Twentieth centuries, combination therapy per se could consist of thyroid gland transplant, or more commonly, consumption of desiccated animal thyroid, thyroid extract, or thyroglobulin. Combination therapy remained the mainstay of therapy for decades despite development of synthetic formulations of T4 and T3, because it was efficacious and cost effective. However, concerns emerged about the consistency and potency of desiccated thyroid hormone after cases were reported detailing either continued hypothyroidism or iatrogenic thyrotoxicosis. Development of the TSH radioimmunoassay and discovery of conversion of T4-to-T3 in humans led to a major transition in clinical practices away from combination therapy, to adoption of levothyroxine "monotherapy" as the standard of care. Levothyroxine monotherapy has a favorable safety profile and can effectively normalize the serum TSH, the most sensitive marker of hypothyroidism. Whether levothyroxine monotherapy restores thyroid hormone signaling within all tissues remains controversial. Evidence of persistent signs and symptoms of hypothyroidism during levothyroxine monotherapy at doses that normalize serum TSH is mounting. Hence, in the last decade there has been acknowledgment by all thyroid professional societies that there may be a role for the use of combination therapy; this represents a significant shift in the clinical practice guidelines. Further bolstering this trend are the recent findings that the Thr92AlaD2 polymorphism may reduce thyroid hormone signaling, resulting in localized and systemic hypothyroidism. This strengthens the hypothesis that treatment options could be personalized, taking into consideration genotypes and comorbidities. The development of long-acting formulations of liothyronine and continued advancements in development of thyroid regenerative therapy, may propel the field closer to adoption of a physiologic thyroid hormone replacement regimen with combination therapy.

Thyroid Function in Aging: A Discerning Approach

Thyroid disease, increasingly common among the general population, is also rising among the elderly, which, given that the global population is aging, constitutes a serious public health issue that needs to be urgently addressed. The most common thyroid disease in younger and older individuals alike is hypothyroidism, including subclinical (SCH) and overt disease. Since TSH tends to increase with age due to intrinsic changes of thyroid metabolism and the gradual resetting of the hypothalamic-pituitary-thyroid axis, the diagnosis of "true" hypothyroidism is challenging, another difficulty being distinguishing disease-specific from aging-associated clinical symptoms. Hypothyroidism in the elderly may cause or exacerbate macrocytic anemia, hypercholesterolemia and kidney dysfunction, therefore careful clinical and biochemical control is necessary. Meanwhile, as an increase of TSH in the old and very old has been associated with longevity, a resetting of the TSH normal range according to age is strongly required before any diagnosis is made and treatment is implemented. Levothyroxine, which remains the treatment of choice, should be initiated in the old at TSH>10 mIU/l, starting with 25 μg/daily followed by cautious upward titration. Recent data (the TRUST study) revealed that treatment of SCH in the elderly does not improve hypothyroid symptoms and the tiredness score when compared with a placebo group. Hyperthyroidism is associated with increased mortality in the aged, this dependent upon type and adequacy of treatment. Treatment should be seriously considered in older patients who have endogenous subclinical hyperthyroidism with a TSH between 0.1 and 0.4 mIU/L, with regular monitoring being strongly advised.

Primary hypothyroidism in the community: Lower daily dosages of levothyroxine replacement therapy for Asian patients

The goal of treatment in patients with primary hypothyroidism is to attain euthyroidism guided by the stipulated thyroid-stimulating hormone (TSH) levels range so as to minimize any potential long-term adverse effects. However, various factors may result in their Levothyroxine (T4) under and over-replacement.Our study aimed to evaluate the mean daily dose of L-T4 replacement for Asian patients with primary hypothyroidism. The secondary aims were to determine the proportion of those who were either over or under-replaced, and the factors associated with their thyroid function status and replacement adherence.Data collected using questionnaire survey from targeted patients managed in a typical public primary care center in Singapore: socio-demographic characteristics, clinical parameters, laboratory investigations, mean daily L-T4-replacement doses, and replacement regimens. The thyroid status of patients was classified based on thyroid function investigations.Complete data of 229 patients were analyzed. A total of 59.8% of patients had TSH within the normal range, 27.5% and 12.7% were under and over-replaced, respectively. About 60% of Asian patients with primary hypothyroidism achieved normal TSH status requiring average of 1.1 μg of daily L-T4/kgBW (kg body weight). Subjects who were over-replaced had a higher daily L-T4 dose/kgBW when compared to the euthyroid and the under replaced groups. Those with L-T4 over-replacement were largely due to excessive dosage. Patients who were younger, from lower socioeconomic strata, and higher BMI were more likely to be over or under-replaced.Majority of Asian patients with hypothyroidism required replacement of 1.1 μg of daily L-T4/kgBW. Their thyroid status was influenced by demographic and dosing factors.

Scope and limitations of iodothyronine deiodinases in hypothyroidism

The coordinated expression and activity of the iodothyronine deiodinases regulate thyroid hormone levels in hypothyroidism. Once heralded as the pathway underpinning adequate thyroid-hormone replacement therapy with levothyroxine, the role of these enzymes has come into question as they have been implicated in both an inability to normalize serum levels of tri-iodothyronine (T3) and the incomplete resolution of hypothyroid symptoms. These observations, some of which were validated in animal models of levothyroxine monotherapy, challenge the paradigm that tissue levels of T3 and thyroid-hormone signalling can be fully restored by administration of levothyroxine alone. The low serum levels of T3 observed among patients receiving levothyroxine monotherapy occur as a consequence of type 2 iodothyronine deiodinase (DIO2) in the hypothalamus being fairly insensitive to ubiquitination. In addition, residual symptoms of hypothyroidism have been linked to a prevalent polymorphism in the DIO2 gene that might be a risk factor for neurodegenerative disease. Here, we discuss how these novel findings underscore the clinical importance of iodothyronine deiodinases in hypothyroidism and how an improved understanding of these enzymes might translate to therapeutic advances in the care of millions of patients with this condition.

Effects of levothyroxine replacement therapy on parameters of metabolic syndrome and atherosclerosis in hypothyroid patients: a prospective pilot study

The aim of this study was to investigate the effect of levothyroxine (LT4) replacement therapy during three months on some parameters of metabolic syndrome and atherosclerosis in patients with increased thyroid-stimulating hormone (TSH) level. This study included a group of 30 female patients with TSH level >4 mIU/L and 15 matched healthy controls. Intima media complex thickness (IMCT) and peak systolic flow velocity (PSFV) of superficial femoral artery were determined by Color Doppler scan. In hypothyroid subjects, BMI, SBP, DBP, and TSH were significantly increased versus controls and decreased after LT4 administration. FT4 was significantly lower in hypothyroid subjects compared with controls and significantly higher by treatment. TC, Tg, HDL-C, and LDL-C were similar to controls at baseline but TC and LDL-C were significantly decreased by LH4 treatment. IMCT was significantly increased versus controls at baseline and significantly reduced by treatment. PSFV was similar to controls at baseline and significantly decreased on treatment. In this study, we have demonstrated the effects of LT4 replacement therapy during three months of treatment on correction of risk factors of metabolic syndrome and atherosclerosis.

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.

Treatment with thyroid hormone

Thyroid hormone deficiency can have important repercussions. Treatment with thyroid hormone in replacement doses is essential in patients with hypothyroidism. In this review, we critically discuss the thyroid hormone formulations that are available and approaches to correct replacement therapy with thyroid hormone in primary and central hypothyroidism in different periods of life such as pregnancy, birth, infancy, childhood, and adolescence as well as in adult patients, the elderly, and in patients with comorbidities. Despite the frequent and long term use of l-T4, several studies have documented frequent under- and overtreatment during replacement therapy in hypothyroid patients. We assess the factors determining l-T4 requirements (sex, age, gender, menstrual status, body weight, and lean body mass), the major causes of failure to achieve optimal serum TSH levels in undertreated patients (poor patient compliance, timing of l-T4 administration, interferences with absorption, gastrointestinal diseases, and drugs), and the adverse consequences of unintentional TSH suppression in overtreated patients. Opinions differ regarding the treatment of mild thyroid hormone deficiency, and we examine the recent evidence favoring treatment of this condition. New data suggesting that combined therapy with T3 and T4 could be indicated in some patients with hypothyroidism are assessed, and the indications for TSH suppression with l-T4 in patients with euthyroid multinodular goiter and in those with differentiated thyroid cancer are reviewed. Lastly, we address the potential use of thyroid hormones or their analogs in obese patients and in severe cardiac diseases, dyslipidemia, and nonthyroidal illnesses.

Combination treatment with T4 and T3: toward personalized replacement therapy in hypothyroidism?

CONTEXT

Levothyroxine therapy is the traditional lifelong replacement therapy for hypothyroid patients. Over the last several years, new evidence has led clinicians to evaluate the option of combined T(3) and T(4) treatment to improve the quality of life, cognition, and peripheral parameters of thyroid hormone action in hypothyroidism. The aim of this review is to assess the physiological basis and the results of current studies on this topic.

EVIDENCE ACQUISITION

We searched Medline for reports published with the following search terms: hypothyroidism, levothyroxine, triiodothyronine, thyroid, guidelines, treatment, deiodinases, clinical symptoms, quality of life, cognition, mood, depression, body weight, heart rate, cholesterol, bone markers, SHBG, and patient preference for combined therapy. The search was restricted to reports published in English since 1970, but some reports published before 1970 were also incorporated. We supplemented the search with records from personal files and references of relevant articles and textbooks. Parameters analyzed included the rationale for combination treatment, the type of patients to be selected, the optimal T(4)/T(3) ratio, and the potential benefits of this therapy on symptoms of hypothyroidism, quality of life, mood, cognition, and peripheral parameters of thyroid hormone action.

EVIDENCE SYNTHESIS

The outcome of our analysis suggests that it may be time to consider a personalized regimen of thyroid hormone replacement therapy in hypothyroid patients.

CONCLUSIONS

Further prospective randomized controlled studies are needed to clarify this important issue. Innovative formulations of the thyroid hormones will be required to mimic a more perfect thyroid hormone replacement therapy than is currently available.

Lipid abnormalities and cardiometabolic risk in patients with overt and subclinical thyroid disease

Dyslipidemia is a common finding in patients with thyroid disease, explained by the adverse effects of thyroid hormones in almost all steps of lipid metabolism. Not only overt but also subclinical hypo- and hyperthyroidism, through different mechanisms, are associated with lipid alterations, mainly concerning total and LDL cholesterol and less often HDL cholesterol, triglycerides, lipoprotein (a), apolipoprotein A1, and apolipoprotein B. In addition to quantitative, qualitative alterations of lipids have been also reported, including atherogenic and oxidized LDL and HDL particles. In thyroid disease, dyslipidemia coexists with various metabolic abnormalities and induce insulin resistance and oxidative stress via a vice-vicious cycle. The above associations in combination with the thyroid hormone induced hemodynamic alterations, might explain the increased risk of coronary artery disease, cerebral ischemia risk, and angina pectoris in older, and possibly ischemic stroke in younger patients with overt or subclinical hyperthyroidism.

Relationship of low-density lipoprotein (LDL) particle size to thyroid function status in Koreans

OBJECTIVE

Dyslipidaemia is a well-known manifestation of thyroid dysfunction. Recently, small low-density lipoprotein (LDL) particle size has been linked with development of cardiovascular disease. To better understand the effects of thyroid dysfunction on the development of cardiovascular disease, we examined LDL particle size and lipid profiles in subjects with different thyroid function.

METHODS

Included were 46 patients with overt hypothyroidism, 57 patients with subclinical hypothyroidism, 46 patients with overt hyperthyroidism, 51 patients with subclinical hyperthyroidism, and 110 age- and sex-matched healthy control subjects. We measured LDL particle size and lipid profiles in these subjects.

RESULTS

No significant differences were found in LDL particle size between the groups with different thyroid function. Serum total cholesterol and LDL-cholesterol levels were significantly higher in the cases of hypothyroidism than in the cases of hyperthyroidism and the healthy control subjects. Serum triglyceride levels were higher in subjects with overt hypothyroidism than in those with overt hyperthyroidism or healthy control subjects.

CONCLUSIONS

LDL particle size, the emerging risk factor for atherosclerosis, did not appear to be significantly affected by the degree of thyroid dysfunction. Increased risk of atherosclerosis in hypothyroidism does not appear to be associated with LDL particle size, the non-traditional cardiovascular risk factor.

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

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

Is annual surveillance of all treated hypothyroid patients necessary?

BACKGROUND

Annual surveillance (with thyroid function testing) is widely recommended for the long-term follow-up of treated hypothyroid patients. It is based largely on consensus opinion and there is limited evidence to support the frequency of monitoring. The majority of patients in our hospital based thyroid register are on 18 monthly follow-up.

METHODS

We carried out a retrospective analysis to see if there is evidence to support more frequent testing. We used a logistic regression model to assess whether any baseline characteristics could be applied to predict an abnormal test.

RESULTS

We identified 2,125 patients with a minimum of 10 years follow-up (89% female, 65% autoimmune hypothyroidism, and mean age at registration 51 years). There were 2 groups: 1182 (56%) had been allocated to 18 monthly follow-up and the rest had annual surveillance. The groups were well matched at baseline. Overall, during follow-up the 12 monthly group had more abnormal tests requiring dose adjustment. However, on logistic regression analysis, people aged less than 60 years, individuals taking < 150 mug thyroxine per day and people on 18 monthly follow-up had less abnormal tests.

CONCLUSION

18 monthly surveillance may be adequate in the long term follow-up of hypothyroid patients less than 60 years of age on a stable thyroxine dose of 100-150 mug/day where there are robust follow-up mechanisms in place. Implementing this strategy has potential for cost saving.

Evaluation response and effectiveness of thyroid hormone replacement treatment on lipid profile and function in elderly patients with subclinical hypothyroidism

Positive effect of thyroid hormone replacement (THR) on lipid profile is well defined. Effectiveness of THR on lipid profile and function among elderly patients with subclinical hypothyroidism (SCH) has not yet been concluded. This is a population-based cross-sectional study. Twenty-six elderly patients with SCH were compared with 31 patients with clinical hypothyroidism (CH). Before the study neither group had received THR therapy. Data on lipid profile, demographic, functional, and cognitive status were obtained at baseline. SCH was defined as an elevated thyroid-stimulating hormone (TSH) level (> 4.67 mU/l) and normal serum free thyroxine (FT(4)) level. Total cholesterol (TC), high-density lipoprotein (HDL) cholesterol, and triglycerides (TG) were measured after overnight fast. The level of lower density lipoprotein (LDL) cholesterol was calculated. Both studied groups received levothyroxyne replacement and re-evaluated after 3 months of euthyroidism. Functional and cognitive status were evaluated by the activity of daily living (ADL) and mini mental state evaluation (MMSE), respectively. Participants with SCH did not differ from patients with CH regarding age, gender, cognitive, and functional status, and prevalence of cardiovascular disease (CD) was similar in both groups. Most patients (24/26) with SCH had TSH levels lower than 10 mU/l. Response to THR therapy regarding the improvement of blood levels of TC, LDL, and TG had a non-significant trend, which seemed to be better in patients with SCH than in those with CH. Decreases, TC/HDL and LDL/HDL ratios were greater in patients SCH (p < 0.0001 and p = 0.0004, respectively) than in patients with CH. Improvement in cognitive and functional status and decrease in mean blood pressure and body mass index (BMI) were found in both of studied groups. It was shown that THR among patients with SCH is beneficial not only by improvement in lipid profile, as well as by improvement in cognitive and functional status, but also in decreasing blood pressure and BMI.

Glucose tolerance and lipid profile in longterm exogenous subclinical hyperthyroidism and the effects of restoration of euthyroidism, a randomised controlled trial

OBJECTIVE

The impact of prolonged subclinical hyperthyroidism on glucose and lipid metabolism is unclear. Therefore, we evaluated glucose and lipid metabolism in patients with differentiated thyroid carcinoma (DTC) on TSH suppressive thyroxine therapy as a model for subclinical hyperthyroidism and investigated whether restoration to euthyroidism affects metabolism.

DESIGN

We performed a prospective, single-blinded, placebo-controlled, randomised trial of 6 months duration with 2 parallel groups.

PATIENTS

Twenty-five subjects with a history of differentiated thyroid carcinoma with > 10 years TSH-suppressive therapy with l-thyroxine completed the study. l-thyroxine dose was replaced by study medication containing l-thyroxine or l-thyroxine plus placebo. Medication was titrated to establish continuation of TSH suppression (low-TSH group, 13 patients) and euthyroidism (euthyroidism group, 12 patients).

MEASUREMENTS

We evaluated glucose metabolism by glucose tolerance test and HOMA (IR) and lipid metabolism by lipid profile. In addition, we measured plasma concentrations of glucoregulatory hormones.

RESULTS

At baseline, glucose tolerance, HOMA (IR), lipid profile and plasma concentrations of glucoregulatory hormones were within the normal range. No significant differences between the low TSH and euthyroidism group were observed. After 6 months, neither glucose nor lipid metabolism in the low TSH group were different from baseline values.

CONCLUSION

In summary, glucose and lipid metabolism in patients with DTC and long-term subclinical hyperthyroidism in general are not affected. Restoration of euthyroidism in general does not affect glucose and lipid metabolism.

Thyroid substitution therapy induces high-density lipoprotein-associated platelet-activating factor-acetylhydrolase in patients with subclinical hypothyroidism: a potential antiatherogenic effect

BACKGROUND

Subclinical hypothyroidism (SH) has been associated with an increased risk of ischemic heart disease, which has been partly attributed to lipid abnormalities. Human plasma platelet-activating factor acetylhydrolase (PAF-AH) is an enzyme associated with lipoproteins (both low-density lipoproteins [LDL], and high-density lipoproteins [HDL]). Plasma paraoxonase 1 (PON1) is an esterase exclusively associated with HDL.

OBJECTIVE

To evaluate qualitative changes in lipoprotein metabolism with respect to PAF-AH and PON1 activities in patients with SH before and after the restoration of euthyroidism.

DESIGN AND METHODS

We determined the PAF-AH activity in plasma and on HDL and PON1 activities as well as the lipid profile patients with SH at baseline and after 6 months of levothyroxine substitution therapy. Thirty normolipidemic healthy individuals comprised the control group.

RESULTS

Compared to controls, patients with SH showed higher levels of total cholesterol, LDL cholesterol, triglycerides, and apolipoprotein B. Triglycerides were significantly reduced after levothyroxine treatment. Patients with SH exhibited higher plasma baseline PAF-AH activity (63.0 +/- 16.5 versus 44.3 +/- 9.5 nmol/mL per minute p < 0.0001) and lower baseline HDL associated PAF-AH (2.9 +/- 1.1 versus 3.6 +/- 0.9 nmol/mL per minute p = 0.02) compared to the control group. PON1 activities were similar in both groups. Levothyroxine treatment had no effect on plasma PAF-AH activity or PON1 activities but resulted in a significant elevation of HDL-associated PAF-AH activity (from 2.9 +/- 1.1 to 3.5 +/- 1.0 nmol/mL per minute, p = 0.003).

CONCLUSIONS

Patients with SH exhibit increased plasma PAF-AH activity and low HDL-associated PAF-AH activity. Levothyroxine induces a significant increase in HDL-PAF-AH activity. This action may represent a potential antiatherogenic effect of thyroid replacement therapy.

Effects of levothyroxine treatment on biochemical and hemostasis parameters in patients with hypothyroidism

OBJECTIVE

The aims of the study were to evaluate the disturbances in the coagulation system in patients with overt hypothyroidism (OH), to assess the effects of levothyroxine (LT4) on the coagulation parameters, and to determine whether subclinical hypothyroidism (SH) affects concentrations of coagulation markers and several biochemical parameters, thereby supporting early substitution.

DESIGN

The study included 15 patients with SH (TSH levels 5-10 mU/l), 15 patients with OH and 15 euthyroid controls.

METHODS

Blood urea nitrogen, creatinine, creatine phosphokinase, aspartate aminotransferase, lactate dehydrogenase, total-cholesterol, high density lipoprotein-cholesterol, low density lipoprotein-cholesterol and triglyceride levels, and bleeding time, prothrombin time (PT), activated partial thromboplastin time (APTT), factor VIII activity, von Willebrand factor activity (vWF), platelet count and clotting time were evaluated just before and three months after the maintenance of euthyroidism with LT4 treatment.

RESULTS

Factor VIII and vWF activities were lower in patients with SH than in controls (P < 0.01). Increased bleeding time, PT, APTT and clotting time and decreased factor VIII activity and vWF activity were observed in patients with OH when compared with controls. Bleeding time, PT, APTT and clotting time decreased and factor VIII activity, vWF and platelet count increased after LT4 in patients with OH. Increases in factor VIII activity and vWF (P < 0.01) were detected also in the SH group with treatment.

CONCLUSIONS

OH is associated with significant abnormalities in clotting parameters which are reversed by LT4. In contrast, SH is associated with minor changes in factor VIII activity and vWF which are reversible by LT4. Serum lipids and other measured parameters are not improved by LT4 in patients with TSH < 10 mU/l and these data fail to demonstrate a need to treat such patients.

Effects of thyroxin therapy on cardiac function in patients with subclinical hypothyroidism: index of myocardial performance in the evaluation of left ventricular function

OBJECTIVE

We investigated the effects of thyroxine (T4) therapy on the cardiac function in subclinical hypothyroidism (SHT) by using the index of myocardial performance (IMP) and the conventional echocardiographic parameters.

METHODS

Forty-five SHT patients (F/M:38/7, age 39.9+/-7.9) and 29 healthy subjects (F/M:25/4, age 38.3+/-8.6) were studied. Patients were randomly assigned, in a double-blind manner to receive T4 therapy (group I) or a placebo (group II) and for a period of up to 12 months, were followed up using thyroid function tests and both conventional and Doppler echocardiographic measurements.

RESULTS

At the baseline, the SHT patients has a significantly higher isovolumic relaxation time (IRT) (98.3+/-23.7 vs. 81.7+/-14.7<0.01), IMP (0.52+/-0.06 vs. 0.42+/-0.05; P<0.001), A max (late mitral peak velocity) (83.4+/-12.6 vs. 74.3+/-13.5; P<0.01) and significantly lower (early mitral peak velocity) Emax/Amax ratio (1.19+/-0.18 vs. 1.34+/-0.17; P<0.01) than the individuals in the control group. In group I, the thyroid hormone profile became normalized after 1 year of L-T4 therapy, but there was no significant change in the left ventricular (LV) morphology or systolic function. After 1 year of follow-up, group I showed a significant reduction of MPI (0.53+/-0.05 vs. 0.42+/-0.07; P<0.001), Amax (84.2+/-13.7 vs. 74.5+/-11; P<0.001) and IRT (98.6+/-23.7 vs. 82.9+/- 23.3; P<0.001) along with a normalization of the E/A ratio (1.17+/-0.16 vs. 1.33+/-0.19; P<0.001). Conversely, no change was observed in group II.

CONCLUSIONS

An impairment of left ventricular diastolic function, which may be reversible with T4 therapy, was observed in the SHT patients, and IMP may be useful in the evaluation of LV myocardial dysfunction in these patients.

Subclinical Hypothyroidism and Cardiovascular Risk

Subclinical hypothyroidism (SH), defined by elevated serum levels of thyroid stimulating hormone (TSH) with normal levels of free thyroid hormones, is common in adults, especially in women over 60 years of age. Among individuals with this condition, up to two-thirds have serum TSH levels between 5-10 mU/L and thyroid autoantibodies; almost half of them may progress to overt thyroid failure, the annual percent risk increasing with serum TSH level. There is evidence that elevated TSH levels in patients with SH do not reflect pituitary compensation to maintain euthyroidism, but a mild tissue hypothyroidism sensu strictu. When lasting more than 6-12 months, SH may be associated with an atherogenic lipid profile, a hypercoagulable state, a subtle cardiac defect with mainly diastolic dysfunction, impaired vascular function, and reduced submaximal exercise capacity. The deviation from normality usually increases with serum TSH level ('dosage effect' phenomenon). Restoration of euthyroidism by levothyroxine (LT4) treatment may correct the lipid profile and cardiac abnormalities, especially in patients with an initially higher deviation from normality and higher serum TSH levels. Importantly, a strong association between SH and atherosclerotic cardiovascular disease, independent of the traditional risk factors, has been recently reported in a large cross-sectional survey (the Rotterdam Study). However, whether SH confers a high risk for cardiovascular disease, and whether LT4 therapy has a long-term benefit that clearly outweighs the risks of overzealous treatment in these individuals, remain topics of controversy. Therefore, until randomized, controlled, prospective, and adequately powered trials provide unequivocal answers to these critical questions, it is advisable to prescribe LT4 therapy on a case-by-case basis, taking into account the risk of progressive thyroid failure and the risk of cardiovascular events.

Epidemiology and prevention of clinical and subclinical hypothyroidism

Iodine deficiency is the most common cause of hypothyroidism worldwide. In persons living in iodine-replete areas, causes are congenital, spontaneous because of chronic autoimmune disease (atrophic autoimmune thyroiditis or goitrous autoimmune thyroiditis [Hashimoto's thyroiditis]), or iatrogenic because of goitrogens, drugs, or destructive treatment for thyrotoxicosis. Screening for congenital hypothyroidism exists and its use prevents mental retardation. The prevalence of spontaneous hypothyroidism is between 1% and 2% and is more common in older women and 10 times more common in women than in men. A significant proportion of subjects have asymptomatic chronic autoimmune thyroiditis and 8% of women (10% of women over 55 years of age) and 3% of men have subclinical hypothyroidism. Approximately one third of patients with newly diagnosed overt hypothyroidism have received destructive therapy for hyperthyroidism and indefinite surveillance is required. There is not much that can be done to prevent the occurrence of spontaneous autoimmune hypothyroidism, but if identified early, something can be done to prevent progression to overt disease. Controversy exists as to whether healthy adults would benefit from screening for autoimmune thyroid disease because a significant proportion of subjects tested will have evidence of mild thyroid failure. Case finding in women at menopause or visiting a primary care physician with nonspecific symptoms appears justified.

Management of patients with thyroid disease: oral health considerations

BACKGROUND

The thyroid gland and its hormones play an important role in the regulation of growth, development and metabolic functions of the body. Thyroid diseases include a group of conditions that can affect the delivery of dental care.

LITERATURE REVIEWED

The authors conducted a MEDLINE search of the medical and dental literature concerning thyroid disease and its management published between 1980 and 2000. The authors found eight published articles concerning this topic in the dental literature; a few of the articles specifically addressed thyroid disease and dental care. They reviewed the medical literature within the scope of provision of dental care.

CONCLUSIONS

The oral health care professional can play a role in the screening of dental patients who have undiagnosed thyroid disease. In addition, to treat patients who have thyroid disease, a thorough understanding of the many related pathological conditions, as well as the signs and symptoms that can occur, is needed. Specific dental treatment protocols for these patients are not found in the medicodental literature published between 1980 and 2000.

CLINICAL IMPLICATIONS

As part of a health care team, the dentist plays an important role in detecting thyroid abnormalities. Modifications of dental care must be considered when treating patients who have thyroid disease.

A 6-month randomized trial of thyroxine treatment in women with mild subclinical hypothyroidism

PURPOSE

The role of thyroxine replacement in subclinical hypothyroidism remains unclear. We performed a 6-month randomized, double-blind, placebo-controlled trial to evaluate the effects of thyroxine treatment for mild subclinical hypothyroidism, defined as a serum thyroid-stimulating hormone level between 5 to 10 microU/mL with a normal serum free thyroxine level (0.8-16 ng/dL).

SUBJECTS AND METHODS

We randomly assigned 40 women with mild subclinical hypothyroidism who had presented to their family practitioners to either thyroxine treatment (n = 23; 50 to 100 microg daily) or placebo (n = 17). Health-related quality of life (Hospital Anxiety and Depression scale, 30-item General Health Questionnaire), fasting lipid profiles, body weight, and resting energy expenditure were measured at baseline and 6 months.

RESULTS

The most common presenting symptoms were fatigue (n = 33 [83%]) and weight gain (n = 32 [80%]). At presentation, 20 women (50%) had elevated anxiety scores and 22 (56%) had elevated scores on the General Health Questionnaire. Thirty-five women completed the study. There were no significant differences in the changes from baseline to 6 months between women in the thyroxine group and the placebo group for any of the metabolic, lipid, or anthropometric variables measured, expressed as the mean change in the thyroxine group minus the mean change in the placebo group: body mass index, -0.3 kg/m(2) (95% confidence interval [CI]: -0.9 to 0.4 kg/m(2)); resting energy expenditure, -0.2 kcal/kg/24 h (95% CI: -1.3 to 1.0 kcal/kg/24 h); and low-density lipoprotein cholesterol, -4 mg/dL (95% CI: -23 to 15 mg/dL). There was a significant worsening in anxiety scores in the thyroxine group (scores increased in 8 of 20 women and were unchanged in 2 of 20) compared with the placebo group (scores increased in 1 of 14 women and were unchanged in 6 of 14; P = 0.03). CONCLUSIONS; We observed no clinically relevant benefits from 6 months of thyroxine treatment in women with mild subclinical hypothyroidism.

Thyroid disease and lipids

The composition and the transport of lipoproteins are seriously disturbed in thyroid diseases. Overt hypothyroidism is characterized by hypercholesterolaemia and a marked increase in low-density lipoproteins (LDL) and apolipoprotein B (apo A) because of a decreased fractional clearance of LDL by a reduced number of LDL receptors in the liver. The high-density lipoprotein (HDL) levels are normal or even elevated in severe hypothyroidism because of decreased activity of cholesteryl-ester transfer protein (CETP) and hepatic lipase (HL), which are enzymes regulated by thyroid hormones. The low activity of CETP, and more specifically of HL, results in reduced transport of cholesteryl esters from HDL(2) to very low-density lipoproteins (VLDL) and intermediate low-density lipoprotein (IDL), and reduced transport of HDL(2) to HDL(3). Moreover, hypothyroidism increases the oxidation of plasma cholesterol mainly because of an altered pattern of binding and to the increased levels of cholesterol, which presents a substrate for the oxidative stress. Cardiac oxygen consumption is reduced in hypothyroidism. This reduction is associated with increased peripheral resistance and reduced contractility. Hypothyroidism is often accompanied by diastolic hypertension that, in conjunction with the dyslipidemia, may promote atherosclerosis. However, thyroxine therapy, in a thyrotropin (TSH)-suppressive dose, usually leads to a considerable improvement of the lipid profile. The changes in lipoproteins are correlated with changes in free thyroxine (FT(4)) levels. Hyperthyroidism exhibits an enhanced excretion of cholesterol and an increased turnover of LDL resulting in a decrease of total and LDL cholesterol, whereas HDL are decreased or not affected. The action of thyroid hormone on Lp(a) lipoprotein is still debated, because both decrease or no changes have been reported. The discrepancies are mostly because of genetic polymorphism of apo(a) and to the differences between the various study groups. Subclinical hypothyroidism (SH) is associated with lipid disorders that are characterized by normal or slightly elevated total cholesterol levels, increased LDL, and lower HDL. Moreover, SH has been associated with endothelium dysfunction, aortic atherosclerosis, and myocardial infarction. Lipid disorders exhibit great individual variability. Nevertheless, they might be a link, although it has not been proved, between SH and atherosclerosis.

Evaluation of the patient with a suspected thyroid disorder

The principal types of thyroid disorders described herein can be recognized and evaluated clinically and biochemically by the obstetrician/gynecologist. Most patients with diffuse goiter should be referred for further evaluation and an RAI scan arranged while this consultation is awaited. Patients with solitary thyroid nodules should be referred for FNAB. Primary hypothyroidism without significant goiter can be treated without specialist referral, except in patients at high risk for ischemic coronary disease or arrhythmia. Primary hyperthyroidism, apart from subacute and postpartum thyroiditis, should be referred for specialist evaluation and definitive therapy. An RAI scan and uptake should be ordered, and beta-blocker therapy can be initiated as interim therapy in symptomatic patients. Patients with secondary (i.e., hypothalamic- or pituitary-based) thyroid dysfunction should always be referred for evaluation and treatment of the primary intracranial cause. There are several causes of abnormal thyroid function tests in apparently euthyroid patients, and the clinical context often provides important evidence of their nature. Clinical judgment is an important factor in knowing when to arrange specialist consultation.

Impressive lipid changes following hypolipidaemic drug administration can unveil subclinical hyperthyroidism

It is well known that thyroid hormones modulate lipoprotein metabolism. Thus, the presence of clinical or subclinical hyperthyroidism may influence lipid parameters of dyslipidaemic patients and the efficacy of hypolipidaemic therapy. Here we present a patient with mixed hyperlipidaemia whose impressive improvement of his lipid profile following ciprofibrate administration pointed towards the diagnosis of asymptomatic underlying subclinical hyperthyroidism.

Subclinical hypothyroidism in obese patients: relation to resting energy expenditure, serum leptin, body composition, and lipid profile

OBJECTIVE

To evaluate whether subclinical hypothyroidism (SH) affects resting energy expenditure (REE) as well as body composition, lipid profile, and serum leptin in obese patients.

RESEARCH METHODS AND PROCEDURES

A total of 108 obese patients with SH defined as normal free thyroxine levels and thyroid-stimulating hormone (TSH) values of > 4.38 microU/ml (mean +/- 2 SD of the values of our reference group of obese patients with normal thyroid function) were compared with a group of 131 obese patients matched for age, sex, and body mass index (BMI) but with normal TSH levels. We assessed estimated daily caloric intake by 7-day recall, REE by indirect calorimetry, body composition by bioelectrical impedance analysis, serum leptin by radioimmunoassay, and lipid profile (i.e., total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides).

RESULTS

All of the variables measured were not different between the euthyroid obese patients and those with SH. In a multiple regression model with REE expressed for kilograms of fat free mass (REE/kgFFM) as a dependent variable and percentage of fat mass, BMI, waist-to-hip ratio, age, TSH, free thyroxine, serum leptin, and caloric intake as independent variables, only percentage of fat mass was significantly correlated with REE/kgFFM in both groups. In the SH group only, BMI, waist-to-hip ratio, age, and TSH were related to REE/kgFFM and explained 69.5% of its variability. After dividing the patients with SH using a cutoff TSH value of 5.7 microU/ml, which represents 3 SD above the mean of TSH levels of the group of obese patients with normal thyroid function, only REE/kgFFM was significantly different and lower in the group of more severely hypothyroid patients.

DISCUSSION

In patients with obesity, SH affects energy expenditure only when TSH is clearly above the normal range; it does not change body composition and lipid profile. We suggest that, at least in obese patients, evaluation of TSH levels may be useful to rule out a possible impairment of resting energy expenditure due to a reduced peripheral effect of thyroid hormones.

Changes in lipoprotein(a) levels in overt and subclinical hypothyroidism before and during treatment

The aim of this prospective, follow-up study was to examine the influence of overt hypothyroidism (OHP) and subclinical (SHP), before and during thyroxine (T4) treatment, on lipoprotein(a) [Lp(a)], other lipoproteins, and apolipoproteins. Twenty-four patients (17 females, 7 males) with OHP, aged 54 +/- 11.1 years (group A) and 23 patients (females) with SHP aged 50.1 +/- 13.2 years (group B) were evaluated and compared to 34 and 38 controls, respectively. All patients received T4 therapy in a stepwise fashion until euthyroidism was reached. Thyrotropin (TSH), free thyroxine (FT4), and total triiodothyronine (TT3) levels were measured before T4 therapy and repeatedly every 4 weeks after the initiation of treatment until the euthyroid state was reached. Levels of Lp(a), total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDLc), high-density lipoprotein cholesterol (HDLc), apolipoprotein A1 (apoA1) and apolipoprotein B (apoB) were measured before and 4 months after the achievement of euthyroidism. Additionally, body mass index (BMI) was also evaluated. We found that in OHP patients, levels of TC, LDLc, and apoB were elevated before treatment and decreased significantly after the return to the euthyroid state. BMI and levels of triglycerides also decreased significantly; Lp(a) was higher in OHP patients in comparison with controls and decreased significantly by 14.56% (25.29% in men and 10.34% in women) during T4 treatment. In SHP patients, levels of all common lipoproteins, apolipoproteins, and Lp(a) did not differ significantly from controls before treatment and did not change after the euthyroid stage was reached. It is concluded that in overt hypothyroidism, Lp(a) levels and most of the lipoproteins were elevated before treatment and decreased significantly. In subclinical hypothyroidism, lipoproteins and Lp(a) levels were normal at baseline and did not change during treatment.

Clinical review 115: effect of thyroxine therapy on serum lipoproteins in patients with mild thyroid failure: a quantitative review of the literature

The objective of our study was to estimate the expected change in serum lipoprotein concentrations after treatment with T4 in patients with mild thyroid failure (i.e. subclinical hypothyroidism). Our data sources included MEDLINE, between January 1966 and May 1999, and review of references from relevant articles. There were 1,786 published studies identified, 461 abstracts reviewed, 74 articles retrieved, 24 articles evaluated against predetermined entry criteria, and 13 studies systematically reviewed and abstracted. All studies reported serum total cholesterol concentration changes during T4 treatment, 12 reported triglyceride changes, 10 reported high-density lipoprotein (HDL) cholesterol changes, and 9 reported low-density lipoprotein (LDL) cholesterol changes. There were 247 patients in 13 studies. The mean decrease in the serum total cholesterol concentration was -0.20 mmol/L (-7.9 mg/ dL), with a 95% confidence interval of -0.09 to -0.34. The decline in serum total cholesterol was directly proportional to its baseline concentration. Studies enrolling hypothyroid participants receiving suboptimal T4 doses reported significantly larger decreases in serum total cholesterol after thyroid-stimulating hormone normalization than studies enrolling previously untreated individuals with mild thyroid failure [-0.44 mmol/L (-17 mg/dL) vs. -0.14 mmol/L (-5.6 mg/dL), P = 0.05]. The change in serum LDL cholesterol concentration was -0.26 mmol/L (-10 mg/dL), with a 95% confidence interval of -0.12 to -0.41. Serum HDL and triglyceride concentrations showed no change. These results, although based on fewer than 250 patients, suggest that T4 therapy in individuals with mild thyroid failure lowers mean serum total and LDL cholesterol concentrations. The reduction in serum total cholesterol may be larger in individuals with higher pretreatment cholesterol levels and in hypothyroid individuals taking suboptimal T4 doses. There do not seem to be significant effects of T4 on serum HDL or triglyceride concentrations.

Cardiovascular and atherogenic aspects of subclinical hypothyroidism

Subclinical hypothyroidism (SH) is common, especially among elderly women. There is no clear evidence to date that SH causes clinical heart disease. However, mild thyroid gland failure, evidenced solely by elevation of the serum thyrotropin (TSH) concentration, may be associated with increased morbidity, particularly for cardiovascular disease, and subtly decreased myocardial contractility. In SH, both cardiac structures and function remain normal at rest, but impaired ventricular function as well as cardiovascular and respiratory adaptation to effort may become unmasked during exercise. These changes are reversible when euthyroidism is restored. Flow-mediated vasodilatation, a marker of endothelial function, is significantly impaired in SH, and decreased heart rate variability, a marker of autonomic activity, suggests hypofunctional abnormalities in the parasympathetic nervous system. SH does result in a small increase in low-density lipoprotein (LDL) cholesterol (C) and a decrease in high-density lipoprotein (HDL)-C, changes that enhance the risk for development of atherosclerosis and coronary artery disease (CAD). After coronary revascularization, a trend toward higher rates of chest pain, dissection, and reocclusion has been noted in SH subjects. Smoking may contribute to the high incidence of SH and may aggravate its metabolic effects. Subjects with SH with marked TSH elevation and high titers of thyroid autoantibodies are at higher risk of unnoticed progression to overt hypothyroidism. Especially women over 50 years with TSH levels greater than 10 mU/L and smoking habits have the highest risk for cardiovascular complications. The magnitude of the lipid changes and the subtle impairment of left ventricular function and cardiopulmonary exercise capacity in SH may justify use of hormone replacement. Early levothyroxine (LT4) treatment in SH may reduce the C level by an average of 8% and normalize all metabolic effects in smokers, nevertheless, in some patients, LT4 therapy may exacerbate angina pectoris or an underlying cardiac arrhythmia. Longitudinal follow-up to define the actual cardiovascular disease risk associated with SH is warranted.

When to treat mild hypothyroidism

The availability and wide acceptance of TSH assays for primary assessment of thyroid function has led to the recognition that mild thyroid hormone deficiency is characterized by elevation of the serum TSH concentration despite a normal free thyroxine level. Other conditions can also cause isolated serum TSH elevation, and these conditions can be distinguished from mild thyroid failure usually based-on clinical and circumstantial observations alone. Thyroxine treatment of patients with mild hypothyroidism has been shown in most, but not all, clinical trials to lower atherogenic lipid levels and relieve certain somatic and neuropsychiatric symptoms. Such treatment also prevents the progression to overt hypothyroidism, which is particularly likely in patients who are older, who have circulating thyroid autoantibodies, or who have a serum TSH greater than 10 mU/L. After the optimal thyroxine dose has been defined, long-term monitoring of patients with an annual clinical evaluation and serum TSH measurement is appropriate. The high prevalence of mild hypothyroidism, particularly in older women, and its subtle clinical presentation have led some authorities to recommend a low threshold for case-finding or routine population screening for the disorder.

Population screening for autoimmune thyroid disease

Whether or not healthy adults in the community would benefit from screening for autoimmune thyroid disease is controversial. Although the prevalence of unsuspected overt thyroid disease is low, a significant proportion of subjects tested will have evidence of mild thyroid failure or excess. This article assesses whether subclinical thyroid disease is of sufficient clinical importance to warrant screening and, once detected and confirmed, to justify therapy. Population screening for autoimmune thyroid disease is assessed against recently revised screening criteria, using data from epidemiologic studies. Recommendations are proposed that may be applied in any iodine-replete community.

Systemic alterations in phospholipid concentrations of blood plasma in patients with thyroid carcinoma: an in-vitro (31)P high-resolution NMR study

In this study in-vitro (31)P high-resolution NMR spectroscopy of human blood plasma was optimized to obtain absolute concentrations of the major plasmaphospholipids: phosphatidylethanolamine plus sphingomyelin (PE + SM), 1- and 2-acyl-lysophosphatidylcholine (LPC1 and LPC2), phosphatidylinositol (PI) and phosphatidylcholine (PC). Plasma spectra of 33 patients with thyroid carcinoma were acquired at 121.49 MHz using a 300 MHz spectrometer. The patients were rendered hypothyroid (TSH >30 mU/l) in preparation for a whole-body scintigraphy. The whole-body scintigraphy showed tumour tissue or metastases in 16 patients (group C). Owing to an inconclusive whole-body scintigraphy, 17 patients were classified as being in remission (group B). After levothyroxine substitution 14 patients of group B were measured in euthyroidism too (group D). Besides these sub-groups, there was a control group made up of 23 healthy volunteers (group A). Group B showed significantly higher PE + SM and PC concentrations than group C (0.59 +/- 0.02 mmol/l PE + SM in B vs 0.48 +/- 0.02 mmol/l in C; 2.1 +/- 0.1 mmol/l PC in B vs 1.6 +/- 0.1 mmol/l in C). In comparison with group D higher concentrations of the phospholipids PE + SM and PC as well as PI were found in group B (0.59 +/- 0.02 mmol/l PE + SM in B vs 0.48 +/- 0.03 mmol/l in D; 0.074 +/- 0.005 mmol/l PI in B vs 0.046 +/- 0.004 mmol/l in D; 2.1 +/- 0.1 mmol/l PC in B vs 1.6 +/- 0.1 mmol/l in D). The data indicate that under the condition of hypothyroidism only patients in remission (group B) show significantly increased phospholipid concentrations, whereas the values in patients with remaining tumour tissue (group C) do not differ from those of the reference groups A and D. This finding is interpreted as an interference between the hormonal status and the systemic effects of cancer.

The blood spot thyrotropin method is not adequate to screen for hypothyroidism in the elderly living in abundant-iodine intake areas: comparison to sensitive thyrotropin measurements

We investigated whether the blood spot thyrotropin (TSH) method was adequate for screening elderly subjects with abundant iodine intake (median excretion 330 microg/g creatinine) for hypothyroidism. In 97 healthy adults (group A), 210 nursing home residents (group B) and 265 elderly subjects living at home (group C) serum (sensitivity < 0.02 mU/L, cost 1.2 U.S. dollars [USD]) and blood spot TSH (sensitivity < 1.0 mU/L, cost 0.4 USD) were measured, and the sensitivity and specificity of different blood spot TSH cutoff points to detect cases with elevated serum TSH were calculated. Elevated (> 3.5 mU/L) serum TSH levels (group A, 6.2%; group B, 16.2%; group C, 22.3%; B > A, p = 0.025; C > A, p < 0.001) were detected with the required sensitivity of greater than 0.9 only if the cutoff point of the blood spot TSH was set as low as 2.5 mU/L, but this led to a considerable loss of specificity. At cutoff point 2.5 mU/L, the rate of positivity was 39.3% and the cost of blood spot screening/person increased to 0.88 USD, considering that positive cases have to be rechecked by serum TSH to exclude false positivity. Cases with significantly elevated (> 10.0 mU/L) serum TSH (group A, 1.03%; group B, 2.85%; group C, 2.20%) were detected at blood spot cutoff points 10.0-4.0 mU/L with a sensitivity of 1.0 and without considerable loss of specificity. We conclude that while screening for hypothyroidism in the elderly population with abundant iodine intake is justified by the high prevalence of elevated ultrasensitive serum TSH values, the sensitivity of the blood spot method is insufficient to detect the subclinical hypothyroidism accurately and would, therefore, fail to detect most affected subjects.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Very-low-density lipoprotein apolipoprotein B100 kinetics in adult hypopituitarism

Hypopituitarism is associated with hyperlipidemia, the mechanisms of which are not fully known. One possible mechanism is an increased hepatic secretion of very-low-density lipoprotein (VLDL) apolipoprotein B100 (apo B100). To investigate this, 13 hypopituitary patients (seven women and six men; age, 46 +/- 3 years [mean +/- SEM]; body mass index [BMI], 29 +/- 2 kg/m2) and 13 matched controls (seven women and six men; age, 43 +/- 3 years; BMI, 28 +/- 2 kg/m2) were investigated in a stable-isotope study. [1-(13)C]leucine (1 mg/kg body weight) was administered, followed by a continuous 6-hour infusion of [1-(13)C]leucine (at a rate of 1 mg/kg/h). Patients had a similar fractional secretion rate (FSR) of VLDL apo B100 versus controls (0.37 +/- 0.05 v 0.38 +/- 0.06 pools/h, respectively), but they had a significantly larger pool size (3.4 +/- 0.3 v 1.9 +/- 0.3 mg/kg) and higher absolute secretion rate ([ASR] 27.8 +/- 2.9 v 16.0 +/- 2.5 mg/kg/d). The increase in hepatic VLDL production may explain the lipid abnormalities found in hypopituitarism. Fasting circulating nonesterified fatty acids (NEFAs) were decreased in the patients (284 +/- 26 v 664 +/- 92 micromol/L, P < .001) despite the increase in VLDL secretion. An inverse relationship was observed between the NEFA level and VLDL apo B100 FSR in the patients (r(s) = -.85, P < .005).

Left ventricular diastolic dysfunction in patients with subclinical hypothyroidism

Although subclinical hypothyroidism is frequently diagnosed, the decision to institute a substitutive therapy with L-T4 remains controversial. Because the cardiovascular system is considered a main target for the action of thyroid hormone, we investigated whether subclinical hypothyroidism induces cardiovascular abnormalities. Twenty-six patients (mean age, 36 +/- 12 yr) were evaluated by Doppler-echocardiography, whereas a subgroup of 10 patients, randomly selected, were reevaluated after 6 months of L-T4 substitutive therapy (mean dose, 68 microg daily). Thirty subjects (matched for age, sex, and body surface area) served as controls. Mean plasma TSH was significantly higher in patients (P < 0.001), whereas mean serum free T4 and free T3 concentrations, although in the normal range, were significantly lower (P < 0.001 and P < 0.005, respectively). Blood pressure and heart rate did not differ from control values. Echocardiogram examination showed no abnormalities of the left ventricular morphology and a slight, but not significant, reduction in the systolic function in the patient group. In contrast, Doppler-derived indices of diastolic function showed significant prolongation of the isovolumic relaxation time (94 +/- 13 vs. 84 +/- 8 msec; P < 0.001), increased A wave (55 +/- 13 vs. 48 +/- 9 cm/sec; P < 0.05), and reduced early diastolic mitral flow velocity/late diastolic mitral flow velocity ratio (1.4 +/- 0.3 vs. 1.7 +/- 0.3; P < 0.001). In the subgroup of 10 patients, thyroid hormone profile was normalized by 6 months of L-T4 substitutive therapy, whereas no changes were observed in the left ventricular morphology. Systolic function was significantly enhanced, as compared with pretreatment values (P < 0.01) but did not differ from control values. Also, systemic vascular resistance was significantly decreased by L-T4 replacement therapy. Assessment of diastolic function showed significant shortening of isovolumic relaxation time (77 +/- 15 vs. 91 +/- 8; P < 0.05), reduction of A wave (51 +/- 13 vs. 60 +/- 12; P < 0.01), and increase of early diastolic mitral flow velocity/late diastolic mitral flow velocity ratio (1.7 +/- 0.4 vs. 1.3 +/- 0.3; P < 0.001). These indices, however, were comparable with those of control subjects. These findings indicate that subclinical hypothyroidism affects diastolic function and that this abnormality may be reversed by L-T4 substitutive therapy.

Subclinical thyroid disease in the elderly

The development of sensitive assays for thyrotropin (TSH) has led to the discovery that many older patients have abnormal TSH levels without other alterations in serum thyroid hormone levels, conditions termed subclinical hypothyroidism (isolated elevation of TSH levels) and subclinical hyperthyroidism (isolated suppression of TSH levels). Subclinical hypothyroidism occurs in 5% to 10% of elderly subjects, and is especially prevalent in elderly women. Subclinical hyperthyroidism is less common, affecting less than 2% of the elderly population. The causes of subclinical thyroid disease in the elderly are similar to those of thyroid disease in the general population, although medications and iodine-containing compounds may play an increased role. Potential risks of subclinical hypothyroidism in the elderly include progression to overt hypothyroidism, cardiovascular effects, hyperlipidemia, and neurological and neuropsychiatric effects. Potential risks of subclinical hyperthyroidism in the elderly include progression to overt hyperthyroidism, cardiovascular effects (especially atrial fibrillation), and osteoporosis. Decisions to treat elderly subjects with subclinical thyroid disease should be based on a careful assessment of these risks in the individual patient.

Thyroid functions and serum lipids in older women: a population-based study

PURPOSE

To determine if thyroid hormone deficiency, manifested by elevated serum thyrotropin (TSH), is associated with alterations in serum lipids in an unselected population of older women.

SUBJECTS AND METHODS

Population-based sampling of 279 ambulatory white women over age 65 studied at four US clinical centers, randomly selected from a cohort of 9,704 participants enrolled in the Study of Osteoporotic Fractures. A third-generation chemiluminescent TSH assay and serum lipid levels--total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides--were measured on fasting sera collected at the baseline visit. The cross-sectional relationships between TSH and lipid levels were analyzed.

RESULTS

TSH was high (>5.5 mU/L) in 19 women (6.8%), and was low (< or =0.1 mU/L) in 10 (3.6%). After multiple adjustment, LDL-C was 17 mg/dL or 13% higher (95% confidence interval [CI] 1%, 25%), and HDL-C was 6.5 mg/dL or 12% lower (CI -0.2%, -25%) in women with high TSH compared with those with normal TSH. The ratio of LDL-C to HDL-C was 29% greater (CI 4%, 53%) among women with elevated TSH. Although total cholesterol was 8% higher among women with high TSH, this difference was not statistically significant (CI -1%, 15%). High TSH was found in 12% of the women with the combination of high cholesterol (>240 mg/dL), high LDL-C (>160 mg/dL), and low HDL-C (<45 mg/dL); likelihood ratio = 1.8) whereas high TSH was found in only 2.2% of women with normal lipids (likelihood ratio = 0.3).

CONCLUSION

Among older white women, high TSH is associated with deleterious changes in serum lipids, particularly HDL-C, LDL-C, and the ratio of LDL-C to HDL-C cholesterol. Women with multiple lipid abnormalities are twice as likely to have an increased TSH.

Effects of iodotyrosines, thyronines, iodothyroacetic acids and thyromimetic analogues on in vitro copper-induced oxidation of low-density lipoproteins

We studied the effect of different thyroid compounds [(I2, monoiodo-L-tyrosine (MIT), diiodo-L-tyrosine (DIT), L-thyronine (T0), 3,5-diiodo-L-thyronine (T2), 3,5,3'-triiodo-L-thyronine (T3), 3,3',5'-triiodo-L-thyronine (rT3), 3,5,3',5'-tetraiodo-L-thyronine (T4), 3,5-diiodothyroacetic acid (TA2), 3,5,3'-triiodothyroacetic acid (TA3) and 3,5,3',5'-tetraiodothyroacetic acid (TA4)] or thyromimetics [(3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) and 3,5-diiodo-3'-isopropyl-thyroacetic acid (IpTA2)] on in vitro copper-induced oxidation of low-density lipoproteins (LDL). Human native LDL (0.05 g protein/L) oxidation was induced by 2.5 micromol/L of CuCl2. Conjugated dienes were measured spectrophotometrically for up to 10 hr. The length of the lag phase (Tlag), maximum velocity of the reaction (Vmax) and the maximum amount of generated dienes were obtained from kinetic data. T3 increased Tlag and decreased Vmax with a dependence upon concentration (0 to 3 micromol/L). There was no difference between the Dmax obtained with Cu2+ alone or in the presence of the various compounds (1 micromol/L). I2, MIT and DIT did not modify any parameter of the oxidation kinetic. T0 and T2 had the same antioxidant efficiency as T3, whereas T4 only decreased Vmax. rT3 increased Tlag less than did T3, whereas DIMIT was the thyronine that had the most important effect. TA2 and TA, were the most efficient antioxidant compounds. TA4 decreased Tlag less than TA3 did, whereas IpTA2 had an effect weaker than that of the physiological acetic derivatives. The data suggest that thyroid hormones and derivatives have LDL-antioxidant properties, their importance being related to their 4'-hydroxy diphenyl ether structure and depending upon the nature and the position of substituents in this structure.

Urinary cortisol metabolites in the assessment of peripheral thyroid hormone action: overt and subclinical hypothyroidism

Biological assessment of peripheral thyroid hormone action may be important in subclinical hypothyroidism, where decision-making is often difficult. The impairment of urinary cortisol metabolites in overt hypothyroidism reflects an acquired 11 beta hydroxysteroid dehydrogenase (11 beta OHSD) deficiency, and is assessed in terms of a reduction in the tetrahydrocortisone (THE)/tetrahydrocortisol (THF) ratio or THE/THE + alpha THF ratio; the alpha THF/THF ratio reflects 5 beta reductase activity. The aim of this study was to determine if urinary cortisol metabolite ratios are a good index of peripheral thyroid hormone action in subclinical hypothyroidism.

MATERIALS AND METHODS

the THE/THF, THE/THF + alpha THF and alpha THF/THF ratios were measured in 24 h urine samples from 3 groups of subjects: 1) 18 euthyroid subjects; 2) 25 patients with elevated serum TSH and low FT4 levels (overt hypothyroidism); and 3) 25 patients with increased serum TSH and normal FT4 levels (subclinical hypothyroidism.

RESULTS

7/25 overtly and 5/25 subclinically hypothyroid patients had a THE/THF + alpha THF ratio below the mean control value -2 SD, while respectively 20/25 and 11/25 patients had a THE/THF ratio below the mean control value -2 SD. The mean THE/THF + alpha THF, THE/THF and alpha THF/THF ratios were significantly different among the 3 groups (ANOVA) and were lower in the overtly hypothyroid group than in the other two groups (Fisher's test); daily urine sodium output was also significantly different between the three groups and lower in the overtly and subclinically hypothyroid groups than in the control group (Fisher's test). FT3 and FT4 both correlated with THE/THF + alpha THF in the overtly hypothyroid patients (r = 0.43; p < 0.05 and r = 0.40; p < 0.05, respectively). In the subclinically hypothyroid patients, TSH correlated with THE/THF + alpha THF (r = 0.44; p < 0.05) and THE/THF (r = 0.43; p < 0.05). FT3, FT4 and TSH levels correlated with THE/THF + alpha THF (p < 0.001), THE/THF (p < 0.001), alpha THF/THF (p < 0.001) and daily natriuresis (p < 0.05) in the whole population (patients + controls). In conclusion, urinary cortisol metabolites, although impaired in overt hypothyroidism, are not an accurate index of peripheral thyroid hormone deficiency in subclinical hypothyroidism. We also identified an increase in the alpha THF/THF ratio in overt hypothyroidism, which may be related to 5 beta reductase disturbances.

Subclinical thyrotoxicosis

Subclinical thyrotoxicosis is defined as low serum thyrotropin (TSH) and normal serum thyroid hormone concentrations. It must be distinguished from nonthyroidal illness and secondary hypothyroidism. The most common causes are excessive thyroid hormone therapy, autonomously functioning thyroid adenoma, multinodular goiter, and Graves' disease, but many patients have no evident thyroid disease. A few patients have minor symptoms and signs of hyperthyroidism. The likelihood of progression to overt thyrotoxicosis is low, and many patients have normal serum TSH concentrations weeks or months later. Treatment should be based on consideration of the cause of the subclinical thyrotoxicosis, and whether the patient has any clinical manifestations of thyroid hormone excess or underlying problems likely to be aggravated by small increases in thyroid secretion.

Beneficial effects of a novel thyromimetic on lipoprotein metabolism

Although L-triiodothyronine (L-T3) lowers cholesterol, this hormone is not used to treat hypercholesterolemia because of its cardiotoxic effects. Thyromimetics, such as the novel compound CGS 23425, that mimic the beneficial but lack the detrimental effects of T3, may be useful in the treatment of hypercholesterolemia. To show that CGS 23425 has no cardiotoxicity, atrial contractility and force were both measured and found to be unchanged in rats treated with up to 10 mg/kg drug. The lipid lowering actions of this drug resulted in a 44% decrease in low-density lipoprotein (LDL) cholesterol in hypercholesterolemic rats treated with 10 microg/kg of the compound. Normal rats required a higher dose of 1000 microg/kg to elicit a similar 50% reduction in LDL cholesterol. Both CGS 23425 or T3 (10 nM) increased the specific binding of 125I-labeled LDL to Hep G2 cells and increased LDL receptor number by 44 and 49%, respectively. These data indicate that CGS 23425 enhances hepatic clearance of serum LDL cholesterol. Normal and fat-fed animals treated with the drug showed a dose-dependent increase in apolipoprotein AI, a protein that promotes the efflux of cholesterol from peripheral tissues. Transient transfection of a rat apolipoprotein AI promoter-chloramphenicol acetyltransferase construct, in human hepatoma cells, showed a dose-dependent increase in chloramphenicol acetyltransferase activity with EC50 values of 2 x 10(-12) M and 10(-10) M for thyroid hormone receptors beta1 and alpha1, respectively, with maximal responses at 10(-7) M. These data indicate that CGS 23425 is a thyromimetic that increases apolipoprotein AI expression via thyroid hormone receptor. In summary, CGS 23425 ameliorates hypercholesterolemia by increasing apolipoprotein A1 and the clearance of LDL cholesterol. Therefore, a compound like CGS 23425 may be useful for the prevention and reversal of atherosclerosis.