Subclinical hyperthyroidism and the risk of dementia. The Rotterdam study

Hibernation model of tau phosphorylation in hamsters: selective vulnerability of cholinergic basal forebrain neurons - implications for Alzheimer's disease

Neurofibrillar tangles made up of 'paired helical filaments' (PHFs) consisting of hyperphosphorylated microtubule-associated protein tau are major hallmarks of Alzheimer's disease (AD). Tangle formation selectively affects certain neuronal types and systematically progresses throughout numerous brain areas, which reflects a hierarchy of neuronal vulnerability and provides the basis for the neuropathological staging of disease severity. Mechanisms underlying this selective neuronal vulnerability are unknown. We showed previously that reversible PHF-like phosphorylation of tau occurs during obligate hibernation. Here we extend these findings to facultative hibernators such as Syrian hamsters (Mesocricetus auratus) forced into hibernation. In this model, we showed in the basal forebrain projection system that cholinergic neurons are selectively affected by PHF-like phosphorylated tau, while gamma-aminobutyric acid (GABA)ergic neurons are largely spared, which shows strong parallels to the situation in AD. Formation of PHF-tau in these neurons apparently does not affect their function as pacemaker for terminating hibernation. We conclude that although formation of PHF-like phosphorylated tau in the mammalian brain follows a certain hierarchy, affecting some neurons more frequently than others, it is not necessarily associated with impaired neuronal function and viability. This indicates a more general link between PHF-like phosphorylation of tau and the adaptation of neurons under conditions of a 'vita minima'.

Favorable clinical heart and bone effects of anti-thyroid drug therapy in endogenous subclinical hyperthyroidism

Although subclinical hyperthyroidism (SCH) has been associated with increased risk of osteoporosis and cardiac arrhythmias, its treatment is still controversial. This study was designed as a prospective, randomized, intervention, control-study with a 1-year follow-up in order to investigate whether normalization of serum TSH in SCH using methimazole has favorable bone and heart clinical effects. Fourteen patients with endogenous SCH (not Graves' disease) were enrolled, 7 (5 women/2 men; group T) were treated with methimazole (2.5-7.5 mg/day), and 7 (5 women/2 men; group C) were followed without treatment; 10 healthy subjects were also included in the study as controls. Serum free-T3 (FT3), free-T4 (FT4) and TSH, thyroid echography, bone stiffness index (SI), as measured by heel ultrasonometry, and 24-h electrocardiography monitoring were obtained. SCH patients exhibited higher systolic and diastolic blood pressure than control subjects. They also had a significantly higher number of both ventricular premature beats (VPB) (mean+/-SEM: 681+/-238 vs 6+/-2 beats/24 h; p<0.02) and atrial premature beats (APB) (mean+/-SEM: 495+/-331 vs 7+/-2 beats/24 h; p<0.0001), and a lower SI (66+/-5 vs 96+/-3; p<0.001). Twelve months after normalization of TSH with the use of methimazole, the number of VPB decreased significantly (947+/-443 vs 214+/-109 beats/24 h; p<0.05) while it remained unchanged in untreated SCH patients (414+/-163 vs 487+/-152 beats/24 h; p=ns). An insignificant therapy effect was observed as far as APB were concerned (826+/-660 vs 144+/-75 beats/24 h; p=ns), however their number increased significantly in the untreated group (463+/-49 vs 215+/-46 beats/24 h; p<0.05). The SI increased significantly as a result of therapy in group T (64.1+/-4.8 vs 70.0+/-5.3; p<0.02) and was further reduced in group C at the end of the study (69.1+/-7.3 vs 62.9+/-7.1; p<0.001). No adverse effect was observed in group T. In conclusion, anti-thyroid therapy seems to have favor-able bone and heart clinical effects in subjects with endogenous SCH.

Associations of Thyroid-Stimulating Hormone and Free Thyroxine Concentrations with Health and Life Satisfaction in Elderly Adults

OBJECTIVE

To analyze associations between thyroid-stimulating hormone (TSH) and free thyroxine (FT4 concentrations and life satisfaction, symptoms, self-rated health, and common neuropsychiatric diseases (depression or dementia) in a community-dwelling elderly population to provide evidence whether to decrease the upper reference limit for TSH or the optimal TSH target in levothyroxine treatment in older adults.

METHODS

In this cross-sectional study, we determined TSH and FT4 concentrations in a thyroid disease-free population of 502 men (median age, 71 years) and 584 women (median age, 73 years) and in a patient group of 49 women (median age, 75 years) with primary hypothyroidism who were stable users of thyroxine treatment. Life satisfaction, self-rated health, depression, and dementia were assessed with specific questions and with tools such as the Self-report Depression Scale and the Mini-Mental State Examination. Independent variables were dichotomized, and associations of these variables with TSH and FT4 levels were assessed in the thyroid disease-free population. Levels of TSH and FT4 in thyroid disease-free women and in women treated with thyroxine were also compared.

RESULTS

After age adjustment, there were no associations between TSH levels and self-rated health, life satisfaction, or most symptoms in the thyroid disease-free population. No associations were found between diagnosed depression or Mini-Mental State Examination results and levels of TSH and FT4. Dementia was associated with higher FT4 concentration in men. Although women treated with thyroxine had TSH levels that were higher than thyroid disease-free women, there were no statistically significant differences in independent variables between these 2 groups.

CONCLUSION

Our results do not support the need to decrease the upper reference limit for TSH or to lower the optimal TSH target in levothyroxine treatment in older adults, as recommended in recent guidelines.

Thyroid hormone regulates endogenous amyloid-beta precursor protein gene expression and processing in both in vitro and in vivo models

Thyroid hormone negatively regulates the amyloid-beta precursor protein (APP) gene in thyroid hormone receptor (TR)-transfected neuroblastoma cells. A negative thyroid hormone response element (nTRE) that mediates this regulation has been identified in the first exon of the APP gene. We demonstrate in an in vivo system that expression of APP mRNA, APP protein, and APP secretase cleavage products in mouse brain is influenced by thyroid status. Adult female mice were made hyperthyroid or hypothyroid for 3 weeks and compared to euthyroid mice. APP gene product expression was increased in hypothyroid mouse brain and reduced in hyperthyroid mouse brain, when compared to euthyroid controls. We observed similar effects of thyroid hormone on endogenous APP gene expression in human neuroblastoma cells. The incidence of hypothyroidism increases with age, and localized hypothyroidism of central nervous system has been reported in some patients with Alzheimer's disease (AD). Reduced action of thyroid hormone on the APP gene may contribute to AD pathology by increasing APP expression and the levels of processed APP products. These findings may be an underlying mechanism contributing to the association of hypothyroidism with AD in the elderly, as well as identifying a potential therapeutic target. Pharmacologic supplementation of thyroid hormone, or its analogs, may reduce APP gene expression and beta amyloid peptide accumulation.

Thyroid Function in Patients With Alzheimer Disease: Implications on Response to Anticholinesterase Treatment

Increasing evidence supports an extensive interrelationship between thyroid hormones and the cholinergic system, which is selectively and early affected in Alzheimer disease (AD). The aim of the present study was to explore thyroid function in patients with AD before and after acetylcholinesterase inhibition treatment to possibly identify variances in response. Thyroid function tests were evaluated in 28 AD patients and 24 age and sex-matched controls. Nineteen of the patients were reevaluated after (4 mo) treatment with donepezil. Serum thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4), the free fractions (fT3, fT4) and thyroid autoantibodies were determined using standard methods. All subjects were clinically euthyroid. Patients presented with higher fT4 and anti-thyroperoxidase levels, as compared with the controls. Significant reduction in T4, fT3, fT4, and anti-thyroperoxidase levels were observed 4 months after treatment. Responders had higher T4 and fT4, than nonresponders, followed by significant reductions after treatment. The above, within the normal range alterations, may represent a direct effect on hormone release from the thyroid gland and/or increased conversion of T4 to T3 within the brain. Higher T4 and fT4 levels before treatment might predict a favorable response to donepezil treatment.

Thyroid hormones, dementia, and atrophy of the medial temporal lobe

CONTEXT

Thyroid function has been related to Alzheimer disease (AD), but it remains unclear whether thyroid dysfunction results from or contributes to developing AD.

OBJECTIVE

The objective of the study was to determine the association between thyroid function and both medial temporal lobe atrophy on brain magnetic resonance imaging (MRI) as putative early sign of AD and risk of dementia.

DESIGN AND PARTICIPANTS

This was a population-based cohort study among 1077 elderly subjects aged 60-90 yr and dementia free at baseline (1995-1996).

MAIN OUTCOME MEASURES

Nonfasting serum levels of TSH, free T(4) (fT(4)), T(3), and rT(3) were available in 1025 subjects followed up for incident dementia until 2005. In a subset of 489 nondemented elderly, we assessed volumes of the hippocampus and amygdala on brain MRI. Subjects using thyroid medication were excluded.

RESULTS

During 5657 person-years of follow-up (mean 5.5 yr), 63 subjects were diagnosed with dementia (46 with AD). TSH and thyroid hormones were not associated with risk of dementia or AD. TSH and T(3) were also not related to brain atrophy, whereas nondemented subjects with higher fT(4) levels had more hippocampal and amygdalar atrophy on MRI. Similar associations were found for rT(3). Excluding subjects with thyroid disorders or incipient AD did not change the results.

CONCLUSION

In our study, TSH was related neither to risk of AD nor with early MRI markers thereof, arguing against an important role of thyroid function in the development of AD. Whether the association of higher fT(4) and rT(3) levels with brain atrophy on MRI has functional significance remains to be elucidated.

The significance of thyroid-stimulating hormone and homocysteine in the development of Alzheimer's disease in mild cognitive impairment: a 6-year follow-up study

Mild cognitive impairment (MCI) represents a transition between normal aging and Alzheimer's disease (AD). The aim of this study was to investigate the predictive value of vitamin B12/folate, homocysteine, standard laboratory parameters, and concomitant diseases for development of AD in persons with an MCI diagnosis. Development of dementia was followed for 6 years in 93 consecutively recruited MCI persons. Information concerning the above factors was obtained from medical journals. Thirty-four percent of participants converted to AD within 6 years. A forward stepwise logistic regression was performed. The odds ratio (OR) for the Mini-Mental State Examination (MMSE) was 0.777; for age, 1.084; and for thyroid stimulating hormone (TSH), 0.287. The OR for homocysteine was 1.287 at 60 years of age and 1.087 at 65 years of age. Lower TSH levels together with the more established factors lower MMSE, higher homocysteine levels, and age were found to be predictive factors of AD. This may have clinical implications with regard to monitoring TSH levels and thyroxin substitution in MCI patients.

Optimisation of thyroid hormone replacement using an automated thyroid register

The high prevalence of thyroid dysfunction requires an efficient and effective means of monitoring and adjustment. We compared the current network of 12,524 patients with thyroid dysfunction with register data prior to 1991 to examine the precision of thyroxine replacement in patients with hypothyroidism and assess locally changing trends in treatment of hyperthyroidism. Since 1991, due to the associated adverse effects of a suppressed thyroid-stimulating hormone (TSH) (<0.03 mU/l), the network has facilitated a significant reduction in the proportion of thyroxine-treated patients with TSH suppression from 58.5% before 1991 to 9.2 +/- 3.8% thereafter. Since 1991, there has been an increased use of radioiodine by 14.3% [95% confidence interval (95% CI): 10.6-17.8] and a reduced use of thyroidectomy by 12.3% (95% CI: 8.8-15.8) to treat hyperthyroid patients compared with before 1991. Between the two treatments, there were no differences in subsequent rates of hypothyroidism or mean thyroxine dosage.

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.

Subclinical hyperthyroidism: clinical features and treatment options

Subclinical hyperthyroidism appears to be a common disorder. It may be caused by exogenous or endogenous factors: excessive TSH suppressive therapy with L-thyroxine (L-T4) for benign thyroid nodular disease, differentiated thyroid cancer, or hormone over-replacement in patients with hypothyroidism are the most frequent causes. Consistent evidence indicates that 'subclinical' hyperthyroidism reduces the quality of life, affecting both the psycho and somatic components of well-being, and produces relevant signs and symptoms of excessive thyroid hormone action, often mimicking adrenergic overactivity. Subclinical hyperthyroidism exerts many significant effects on the cardiovascular system; it is usually associated with a higher heart rate and a higher risk of supraventricular arrhythmias, and with an increased left ventricular mass, often accompanied by an impaired diastolic function and sometimes by a reduced systolic performance on effort and decreased exercise tolerance. It is well known that these abnormalities usually precede the onset of a more severe cardiovascular disease, thus potentially contributing to the increased cardiovascular morbidity and mortality observed in these patients. In addition, it is becoming increasingly apparent that subclinical hyperthyroidism may accelerate the development of osteoporosis and hence increased bone vulnerability to trauma, particularly in postmenopausal women with a pre-existing predisposition. Subclinical hyperthyroidism and its related clinical manifestations are reversible and may be prevented by timely treatment.

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.

Long-term incidence of hypothyroidism after radiotherapy in patients with head-and-neck cancer

PURPOSE

To determine the long-term incidence of postirradiation hypothyroidism (HT) in patients with head-and-neck cancer.

METHODS AND MATERIALS

The incidence of overt HT was assessed prospectively in 391 patients with nonthyroid head-and-neck cancer admitted for radiotherapy (RT) consecutively between 1990 and 1996. Eighty-three patients were excluded from the analysis because of known thyroid disease before treatment (n = 27), no RT was given (n = 15), or inadequate follow-up (n = 41). Overt HT was defined as increased thyroid-stimulating hormone (TSH) in combination with decreased fT4/T4 or in combination with initiation of thyroxine replacement therapy.

RESULTS

With a median follow-up of 4.2 years (range, 3 months to 10.9 years) for 308 evaluable patients, the 5- and 10-year Kaplan-Meier actuarial risks of HT were 20% and 27%, respectively. The median time until development of HT was 1.8 years (3 months to 8.1 years). Multivariate analysis showed that patients with bilateral RT to the neck had a higher risk of HT in comparison with unilateral neck RT (relative hazard, 0.37; p = 0.02). The addition of surgery to RT increased the overall risk of HT (p < 0.001); and if surgery involved the thyroid gland, the relative hazard was 4.74 (p < 0.001). For an elevated pre-RT TSH value, the relative hazard was 1.58 (p < 0.001).

CONCLUSION

The incidence of overt HT after locoregional RT for nonthyroid head-and-neck cancer continues to increase with time, even after long-term follow-up. We recommend life-long TSH testing in these patients.

Thyroid function, depressed mood, and cognitive performance in older individuals: the Maastricht Aging Study

The hypothesis was tested that thyroid function, as indicated by serum thyroid-stimulating hormone (TSH) level, is associated with cognitive performance in a healthy aging population. In a random sample of 120 participants recruited from the Maastricht Aging Study (MAAS), aged between 49 and 71 years, we assessed TSH level, mood state (Symptom Check List, subscale depression), and three domains of cognitive function: verbal memory, general sensorimotor speed, and complex flexibility. After correction for age, sex, and educational level, a negative association between TSH and memory function was apparent: higher levels of TSH predicted lower levels of memory performance. Exclusion of individuals with TSH levels suspect for thyroid disorder (n=2) or who were on thyroid replacement (n=3) attenuated this association. Furthermore, additional control for mood status reduced the association below the significance level. No interaction between age and TSH on cognition was found, which indicated that the TSH-memory association was independent of age group level. We conclude that the association between TSH level and memory performance was small and dependent on mood status and the presence of (possible) thyroid disease in this relatively healthy population based sample. Prospective studies are needed to address the role of thyroid function in age-related cognitive decline.

Can dementia be prevented? Brain aging in a population-based context

As a consequence of global aging of the human population, the occurrence of cognitive impairment and dementia is rapidly becoming a significant burden for medical care and public health systems. By the year 2020, the WHO predicts there will be nearly 29 million demented people in both developed and developing countries. Primary and secondary prevention of dementia through individual and population-level interventions could reduce this imminent risk. Vascular risk factors such as type 2 diabetes, hypertension, dietary fat intake, high cholesterol, and obesity have emerged as important influences on the risk of both vascular and Alzheimer's dementia. Understanding the reasons for differences between populations in genetic vulnerability and environmental exposures may help to identify modifiable risk factors that may lead to effective prevention of vascular and Alzheimer's dementia.

Disfunções mínimas da tiróide: hipotiroidismo subclínico e hipertiroidismo subclínico

Hipotiroidismo subclínico (SHT) e hipertiroidismo subclínico (SCH) são definidos pelas concentrações normais de T4 e T3 livres séricos associadas com valores de TSH elevado (SHT) ou suprimido (SCH). As prevalências são baixas e sintomas e sinais de disfunção tiroideana escassos. No SHT, colesterol total e LDL-C estão ligeiramente elevados, e tratamento com levotiroxina pode influir nos valores dos lipídeos. Ocorre diminuição da contratilidade do miocárdio e aumento da resistência vascular periférica, que melhoram com o tratamento. Fibrilação atrial é mais freqüente no SCH, e há aumento do índice de massa do ventrículo esquerdo, da contratilidade cardíaca, disfunção diastólica e indução de batimentos atriais ectópicos que regridem com uso de beta-bloqueadores. No SCH, ocorre diminuição da densidade óssea. Depressão, doença do pânico e alterações de testes cognitivos são freqüentes no SHT. O tratamento do SHT é indicado com TSH sérico maior do que 8mU/L e presença de anticorpos antitiroideanos, e do SCH endógeno, quando existem sintomas, em idosos ou concentração de TSH menor do que 0,1mU/L.

The management of subclinical hyperthyroidism by thyroid specialists

Subclinical hyperthyroidism is a relatively common condition for which prospectively derived evidenced-based management guidelines do not exist. We have conducted a case-based mail survey to solicit opinions from members of the American Thyroid Association (ATA) about various issues that arise in the management of patients with this disorder. The survey was completed and returned by 185 of 300 (62%) of the original survey recipients. Four hypothetical cases varying in age, thyrotropin (TSH) level and underlying etiology were presented. The majority of respondents recommended further evaluation of all cases, most commonly choosing a radioactive iodine uptake (42%-71%), thyroid scan (39%-68%) and antithyroid (TPO/Tg) antibodies (49%-55%) as the additional tests to be ordered. The large majority (84%) recommended observation rather than active treatment for a young patient with a low but detectable serum TSH level. A small majority also recommended observation alone for a young woman with an undetectable serum TSH level (58%) and for an older woman with a low but detectable serum TSH value (63%). However, the majority (66%) favored treating an older woman with an undetectable serum TSH. When treatment was advised in the patients with subclinical hyperthyroidism, the respondents strongly favored anti-thyroid drugs when the etiology was Graves' disease and radioactive iodine when the etiology was toxic nodular thyroid disease. In the absence of adequate evidence-based guidelines, it is hoped that this survey of expert opinions may provide useful guidance for physicians providing care for patients with subclinical hyperthyroidism.

Thyroid disease

Evaluation and treatment of thyroid disease is a common feature of primary care medicine. Nevertheless, the dose of thyroid hormone used to treat hypothyroidism is frequently not titrated to normalize the TSH, engendering the risks of under- or overtreatment. Other hypothyroid patients remain symptomatic even with normalized TSH on levothyroxine alone. Some of these patients improve symptomatically when liothyronine is added to the treatment regimen. Subclinical hypothyroidism and hyperthyroidism are also relatively common in primary care medical practice, and appropriately selected patients probably benefit from treatment. In the follow-up of patients treated for thyroid cancer, the use of rhTSH improves patient comfort considerably while allowing sensitive screening for persistent or recurrent cancer.

Reversible paired helical filament-like phosphorylation of tau is an adaptive process associated with neuronal plasticity in hibernating animals

Neurofibrillary pathology [paired helical filaments (PHFs)] formed by the microtubule-associated protein tau in a hyperphosphorylated form is a major hallmark of Alzheimer's disease and related disorders. The process of tau phosphorylation, thought to be of critical importance for PHF formation, and its potential link to neurodegeneration, however, is not understood very well, mostly because of the lack of a physiological in vivo model of PHF-like tau phosphorylation. Here we describe the formation of highly phosphorylated tau, containing a number of PHF-like epitopes in torpor during hibernation. PHF-like phosphorylation of tau was not associated with fibril formation and was fully reversible after arousal. Distribution of PHF-like tau followed a consistent pattern, being most intense in the entorhinal cortex, hippocampus, and isocortical areas. Within the hippocampus, a particularly high labeling was seen in CA3 pyramidal cells. Somewhat lesser reactivity was present in CA1 neurons while dentate gyrus granule cells were not reactive. Formation of PHF-like tau in CA3 neurons was paralleled by the regression of synaptic contacts of the mossy fiber system terminating on CA3 apical dendrites. Mossy fiber afferentation was re-established during arousal, concomitantly with the decrease of PHF-like tau in CA3 neurons. These findings implicate an essential link between neuronal plasticity and PHF-like phosphorylation of tau. The repeated formation and degradation of PHF-like tau might, thus, represent a physiological mechanism not necessarily associated with pathological effects. Hibernation will, therefore, be a valuable model to study the regulation of PHF-like tau-phosphorylation and its cell biological sequelae under physiological in vivo conditions.

Relation between apolipoprotein E genotype, hepatitis B virus status, and thyroid status in a sample of older persons with Down syndrome

Dementia of the Alzheimer type (DAT) is common in older persons with Down syndrome (DS). There are three common alleles of the apolipoprotein E (ApoE) gene (Sigma 2, Sigma 3, and Sigma 4) resulting in three different isoforms (E2, E3, and E4) and six different genotypes (2,2; 2,3; 2,4; 3,3; 3,4; and 4,4). Sigma 4 is a risk factor for DAT whereas Sigma 2 appears prophylactic. As hepatitis B virus (HBV) infection and hypothyroidism also are common in DS, we evaluated associations between ApoE type, HBV status, and thyroid status in a sample of older persons with DS (n = 55; mean age, 44.3 +/- 10.8 years) using chi-squared analysis. Participants were classified as E2 (2,2 or 2,3), E3 (3,3), or E4 (3,4 or 4,4); positive for markers of HBV infection in the present or past (i.e., total HBcAb+ and/or HBsAg+ with or without infectivity, defined as HBV+) or negative for markers of HBV infection (defined as HBV-) and, currently receiving thyroid hormone supplement (defined as "hypothyroidism") or having normal thyroid function. The majority of the HBV+ were currently HBcAb+ and HBsAb+, but not HBsAg+. In females, there was an ApoE allele effect on thyroid status (P < or = 0.01), E2 being negatively (P < or = 0.01) and E4 being positively (P < or = 0.05) associated with "hypothyroidism". There was no evidence for an ApoE allele effect on thyroid status in males. There was no evidence for an ApoE allele effect on HBV status, or for an HBV status effect on thyroid status. As thyroid status can affect cognitive function, ApoE allele effects in DAT may, in part, be thyroid effects.

Subclinical thyroid disorders: the menace of the Trojan horse

This review aims at summarizing some new data regarding the so-called subclinical thyroid disease and incorporate the knowledge in order to provide a basis for a more careful approach to these morbidities. SHyper represents a considerable risk factor for atrial fibrillation in the elderly and also for osteoporosis, which is a major cause of morbidity in postmenopausal women. SHypo is not an innocuous condition. It progresses to thyroid failure in patients with positive thyroid antibodies, it affects neurobehavior, it may influence cardiac contractility at exercise and it is associated with an impaired lipid profile that may provoke atherosclerosis. Therefore, both conditions should be screened more carefully in the community and treatment should be more often considered.

Basal TSH levels compared with TRH-stimulated TSH levels to diagnose different degrees of TSH suppression: diagnostic and therapeutic impact of assay performance

BACKGROUND

The estimated prevalence of endogenous subclinical hyperthyroidism varies from 4% to 6% and a basal thyroid stimulating hormone (TSH) level < 0.5 mU L-1 may be associated with increased mortality in subjects over 60 years of age who are not on thyroid medication. Exogenous TSH suppression is a mainstay in the treatment of thyroid cancer. Because of recent concerns about potential adverse effects, especially of endogenous TSH suppression on bone, the cardiovascular system and cognitive functions, subclinical hyperthyroidism obtained new clinical importance. We therefore re-evaluated the diagnostic value of basal and thyrotrop in TRH-stimulated serum TSH measurements using TSH assays with different sensitivities.

MATERIALS AND METHODS

A total of 805 oral and nasal TRH stimulation tests were performed on 409 ambulatory subjects with low basal serum TSH concentrations of less than 0.1 mIU L-1. Basal serum TSH was measured either using a second generation assay (functional sensitivity > 0.03 mIU L-1) or two third generation assays (functional sensitivity 0.01 mIU L-1 and 0.007 mU L-1, respectively). Serum TSH concentration was determined before and 3 h after oral administration of 40 mg of TRH and before and 30 min after nasal administration of 2 mg of TRH.

RESULTS

In the oral testing group, the basal TSH levels measured by the different TSH assays were 0.06 +/- 0.03, 0.04 +/- 0.02 and 0.03 +/- 0.02, respectively, whereas the peak TSH levels were 0.4 +/- 0.6, 0.4 +/- 0.6 and 0.3 +/- 0.5 in the patients with subclinical hyperthyroidism. In overt hyperthyroidism, the basal TSH levels were 0.06 +/- 0.02, 0.03 +/- 0.02 and 0.03 +/- 0.02, whereas the peak TSH levels were 0.19 +/- 0.3, 0.16 +/- 0.3 and 0.15 +/- 0.2, respectively. Basal TSH values could discriminate between different degrees of TSH suppression if measured with a third generation assay (P < 0.001), but not with a second generation assay. There was only a weak correlation between basal TSH and peak TSH when measured by a second generation assay (n = 126; r = 0.3; P < 0.001) in contrast to the strong correlation found using the third generation assays (n = 128; r = 0.7; P < 0.001 and n = 69; r = 0.8; P < 0.001, respectively).

CONCLUSIONS

In view of the recent concerns about potential adverse effects in TSH suppression and based on our data, it is mandatory to select a TSH assay with a functional sensitivity of < or = 0.01 mIU L-1 for optimal titration of L-T4 suppressive therapy, especially in patients with thyroid cancer. If, however, only a second generation TSH assay is available, additional TRH testing allows a more careful titration of suppressive thyroxine therapy.

Dementia: when is it not Alzheimer disease?

The advent of symptomatic therapies for Alzheimer disease has placed increasing emphasis on early diagnosis of the dementia syndrome and its various types. This article reviews the definition and epidemiology of the condition that affects up to 50% of all Americans over the age of 80. Also discussed are the main causes of dementia, focusing on those that are not Alzheimer disease and a diagnostic approach that is based on guidelines recently published by the American Academy of Neurology.

Barriers to remember: brain-targeting chemical delivery systems and Alzheimer's disease

Brain-targeted chemical delivery systems (CDSs) represent rational drug design attempts not only to deliver but also to target drugs to their site of action. Using a sequential metabolism approach, the special bidirectional properties of the blood-brain barrier can be exploited to smuggle the precursors of therapeutic compounds across the barrier and lock them inside the brain ready for sustained release of the active drugs. Many potential therapeutic applications can be envisioned for such CDSs; here, the potential of brain-targeted estradiol for the prevention and treatment of Alzheimer's disease is reviewed in detail.