Thyrotrophin-releasing hormone as a thyroid-function test

Isolated anterior pituitary dysfunction in adulthood

Hypopituitarism is defined as a complete or partial deficiency in one or more pituitary hormones. Anterior hypopituitarism includes secondary adrenal insufficiency, central hypothyroidism, hypogonadotropic hypogonadism, growth hormone deficiency and prolactin deficiency. Patients with hypopituitarism suffer from an increased disability and sick days, resulting in lower health status, higher cost of care and an increased mortality. In particular during adulthood, isolated pituitary deficits are not an uncommon finding; their clinical picture is represented by vague symptoms and unclear signs, which can be difficult to properly diagnose. This often becomes a challenge for the physician. Aim of this narrative review is to analyse, for each anterior pituitary deficit, the main related etiologies, the characteristic signs and symptoms, how to properly diagnose them (suggesting an easy and reproducible step-based approach), and eventually the treatment. In adulthood, the vast majority of isolated pituitary deficits are due to pituitary tumours, head trauma, pituitary surgery and brain radiotherapy. Immune-related dysfunctions represent a growing cause of isolated pituitary deficiencies, above all secondary to use of oncological drugs such as immune checkpoint inhibitors. The diagnosis of isolated pituitary deficiencies should be based on baseline hormonal assessments and/or dynamic tests. Establishing a proper diagnosis can be quite challenging: in fact, even if the diagnostic methods are becoming increasingly refined, a considerable proportion of isolated pituitary deficits still remains without a certain cause. While isolated ACTH and TSH deficiencies always require a prompt replacement treatment, gonadal replacement therapy requires a benefit-risk evaluation based on the presence of comorbidities, age and gender of the patient; finally, the need of growth hormone replacement therapies is still a matter of debate. On the other side, prolactin replacement therapy is still not available. In conclusion, our purpose is to offer a broad evaluation from causes to therapies of isolated anterior pituitary deficits in adulthood. This review will also include the evaluation of uncommon symptoms and main etiologies, the elements of suspicion of a genetic cause and protocols for diagnosis, follow-up and treatment.

Evaluation of Thyroid Function in Patients Treated with Continuous Ambulatory Peritoneal Dialysis (CAPD)

Abnormal thyroid function has been described in chronic renal insufficiency, and further changes occur with increasing time on hemodialysis. This study on two groups of patients was done to determine whether treatment with CAPD induces changes in thyroid function. Group A included 16 patients with an average duration of treatment of 2.1 ± 1.1 months; group B included 12 patients with 8.1 ± 2 months. We measured total T4 and T3, free T4, TBG, RT3U, FTI, T4/T3 and basal TSH, and TSH induced by TRH stimulation in plasma, and total and free T4 in dialysate. The results showed a significant decrease in total T4 and T3 in plasma, but no change in free T4 or TSH and no appreciable amounts of the hormones in the dialysate. We believe the decrease in total T4 and T3 is secondary to alterations in transport proteins while thyroid function is maintained by normal free T4 and TSH levels more dependable parameters for the interpretation of thyroid function in chronic diseases.

A combined form of hypothyroidism in pubertal patients with non-mosaic Klinefelter syndrome

Klinefelter syndrome has been associated with thyroid abnormalities, the genesis of which is not yet fully clear. The aim of this study was to evaluate thyroid function in Klinefelter syndrome subjects during the pubertal period. Chemiluminescent microparticle immunoassay was used to analyze Thyroid-Stimulating Hormone, fT3 and fT4 concentration in serum samples from 40 Klinefelter syndrome pubertal boys with classic 47,XXY karyotype and 157 healthy age-matched controls. 13 Klinefelter syndrome patients also underwent Thyrotropin-Releasing Hormone testing to evaluate hypothalamic-pituitary function. fT3 levels were significantly lower in Klinefelter syndrome patients than in age-matched controls (p < 0.001). No significant differences were found for Thyroid-Stimulating Hormone (p = 0.138) or fT4 (p = 0.274), but the serum levels of Klinefelter syndrome patients tended to cluster around the lower part of the reference range for the assay. Three of the thirteen Klinefelter syndrome patients undergoing the Thyrotropin-Releasing Hormone test had an adequate response, one had a prolonged response at 60 min and nine responded inadequately. This study demonstrated for the first time that pubertal Klinefelter syndrome patients have significantly lower fT3 serum levels than do healthy age-matched boys, whereas Thyroid-Stimulating Hormone and fT4 are normal, albeit at the lower end of the reference range. Most patients showed an inadequate/prolonged response to pituitary stimulation with Thyrotropin-Releasing Hormone. These findings suggest a combined form of both central and peripheral hypothyroidism in Klinefelter syndrome boys during pubertal development.

Mitotane treatment in patients with adrenocortical cancer causes central hypothyroidism

INTRODUCTION

Mitotane, a steroidogenesis inhibitor with adrenolytic properties used to treat adrenocortical cancer (ACC), can affect thyroid function. A reduction of FT4 levels with normal FT3 and TSH has been described in these patients. Using an in vitro murine model, the secretory capacity of thyrotrophic cells has been shown to be inhibited by mitotane.

OBJECTIVE

To investigate the pathogenesis of thyroid abnormalities in mitotane-treated patients with ACC.

PATIENTS AND METHODS

In five female patients with ACC (median age 47; range 31-65) treated with mitotane (dosage 1·5 g/day; 1·0-3·0), we analysed the pattern of TSH and thyroid function index (FT4, FT3 and FT3/FT4 ratio) compared to an age- and gender-matched control group. The in vivo secretory activity of the thyrotrophic cells was evaluated using a standard TRH test (200 μg), and the response was compared to both a group of age-matched female controls (n = 10) and central hypothyroid patients (n = 10).

RESULTS

Basal TSH (median 1·54 mU/l; range 1·20-2·17) was normal and scattered around our median reference value, FT3 levels (median 3·80 pmol/l; 3·30-4·29) were normal but below the median reference value of 4·37 pmol/l and FT4 levels were below the normal range in all patients (median 8·40 pmol/l; 7·6-9·9). FT3/FT4 ratio was in the upper range in 4 patients and higher than normal in one patient. A blunted TSH response to TRH was observed in mitotane-treated patients. ΔTSH (absolute TSH response, peak TSH minus basal TSH) was 3·65 (range 3·53-5·26), 12·37 (range 7·55-19·97) and 1·32 mU/l (range 0·52-4·66) in mitotane-treated patients, controls and central hypothyroid patients, respectively. PRL secretion was normal.

CONCLUSIONS

Mitotane-treated patients with ACC showed low FT4, normal FT3 and TSH and impaired TSH response to TRH, characteristic of central hypothyroidism. Furthermore, the elevated FT3/FT4 ratio of these subjects reflects an enhanced T4 to T3 conversion rate, a compensatory mechanism characteristic of thyroid function changes observed in hypothyroid conditions. This finding thus confirms in vitro studies and may have a therapeutic implication for treatment with thyroid hormones, as suggested by current guidelines for this specific condition.

New analytical application of antibody-based biosensor in estimation of thyroid-stimulating hormone in serum

BACKGROUND

Conventionally, ELISA is used to measure thyroid-stimulating hormone (TSH) for diagnosis of thyroid disease. In this study, an immunosensor-based, kinetic-exclusion analysis (KinExA) was used for TSH estimation.

METHODOLOGY

A PMMA microbead column coated with TSH antigen is formed inside the flow cell. Samples consisting of mouse anti-TSH monoclonal antibody and TSH antigen complex in solution are passed over the beads and the unbound anti-TSH antibody is captured by the TSH-coated beads, followed by passing fluorescent-labeled antibody over the beads to generate signals for analysis. The limit of detection for the assay was 0.4 mIU l(-1) and the precision was acceptable.

CONCLUSION

The developed sensor was advantageous due to the automated nature and its convenience, without compromising the sensitivity for estimation of TSH.

Central hypothyroidism

Central hypothyroidism is defined as hypothyroidism due to insufficient stimulation by thyroid stimulating hormone (TSH) of an otherwise normal thyroid gland. It has an estimated prevalence of approximately 1 in 80,000 to 1 in 120,000. It can be secondary hypothyroidism (pituitary) or tertiary hypothyroidism (hypothalamus) in origin. In children, it is usually caused by craniopharyngiomas or previous cranial irradiation for brain tumors or hematological malignancies. In adults, it is usually due to pituitary macroadenomas, pituitary surgeries or post-irradiation. Fatigue and peripheral edema are the most specific clinical features. Diagnosis is established by the presence of normal to low-normal TSH on the background of low-normal thyroid hormones, confirmed by the thyrotropin releasing hormone stimulation test. Therapy includes use of levothyroxine titrated to improvement in symptomology and keeping free T4 in the upper limit of normal reference range.

In-hospital ventricular fibrillation and its relation to serum potassium

Serum potassium (S-K) has been related to the incidence of ventricular fibrillation (VF) before admission to, and during observation in a coronary care unit (CCU). The series comprises 1315 patients. Acute myocardial infarction (AMI) was diagnosed in 537 patients. VF occurred in 46 patients. Fourteen of these had their VF before admission to the CCU. The incidence of VF within 12 h after CCU admission (early VF) was significantly raised (p less than 0.01) in patients with an initial S-K less than 3.9 mmol . l-1. In this group, the incidence of early VF in all patients and in those with AMI amounted to 3.0 and 5.4%, respectively. Corresponding figures in patients with an initial S-K of 3.9 mmol . l-1 or above were 0.6 and 1.5%. Thus, a near 5-fold increase in the incidence of early VF was observed with a S-K below 3.9 mmol . l-1. Patients with VF occurring later than 12 h after admission had significantly higher S-K values than those with early VF. In AMI, the risk of primary and secondary VF seemed to be equally increased with low initial S-K values. There was a strong correlation between myocardial infarction size and the risk of VF. No relationship, however, was noted between infarction size and initial S-K.

Pituitary fuction during X-ray treatment of the hypothalamic-pituitary region as evaluated by the TRH test response

The effect of conventional radiotherapy on the TRH response was studied in fourteen patients, all but one previously surgically treated for pituitary tumors. No change in the TSH response to TRH could be observed either during or after a four week treatment period, thus demonstrating relative resistance of the pituitary gland against irradiation in these patients. We also conclude that the diagnostic value of the TRH test remains unhampered during and in the immediate period after irradiation.

An evaluation of the thyrotrophin-releasing hormone stimulation test in paediatric clinical practice

AIM

The aim of this retrospective study was to evaluate the clinical usefulness of the thyrotropin-releasing hormone (TRH) test in children with suspected hypothalamic or pituitary dysfunction.

METHODS

We reviewed the case notes of all patients in whom a TRH test had been performed over a 6-year period. Group 1 (n = 85, 34 males, aged 0.9-18.8 years) was the reference group with no evidence of hypothalamic, pituitary or thyroid dysfunction. Group 2 (n = 42, 24 males, 0.1-18.0 years) were being investigated for possible pituitary or hypothalamic insufficiency.

RESULTS

In Group 1, thyrotropin (TSH) responses were higher in females than males (p < 0.01). In Group 2, TSH responses were normal for gender in 26 patients, subnormal in 5, and exaggerated/delayed in 11. Four patients with normal TSH responses and 4 with exaggerated/delayed responses had persistently low free thyroxine (FT(4)) or later developed low FT(4) and were treated with thyroxine. All those with subnormal TSH responses had normal FT(4) and were not treated. The TRH test did not reliably discriminate between hypothalamic and pituitary disorders.

CONCLUSIONS

The TRH test did not give useful clinical information. Clinical decisions regarding thyroxine treatment were based on FT(4), not the TRH test. The TRH test should be abandoned in paediatric practice.

Is the thyrotropin-releasing hormone test necessary in the diagnosis of central hypothyroidism in children

To determine the value of the TRH test, we analyzed the unstimulated serum T(4) and TSH concentrations in 54 children with central hypothyroidism. A TRH test was performed in 30 patients. Midline brain defects (septo-optic dysplasia, 28; holoprosencephaly, 2) and combined pituitary hormone deficiencies were present in 30 and 52 patients, respectively. The mean serum free T(4), total T(4), and basal TSH concentrations were 0.6 ng/dl, 4.0 microg/dl, and 2.8 microU/ml, respectively. Five patients demonstrated elevated basal serum TSH concentrations. A normal TRH test [increase (delta) in TSH, 4.5-17.8], based on data from 30 controls, was documented in 23.3% of patients. Brisk (deltaTSH, >17.8), absent/blunted (deltaTSH, <4.5), and delayed responses were documented in 16.7%, 30%, and 30% of patients, respectively. The mean age at diagnosis was 2.8 yr, with 8 patients evolving into TSH deficiency. It was not possible to differentiate patients as having pituitary or hypothalamic disease based solely on the TRH test results. Patients with septo-optic dysplasia were diagnosed earlier and had elevated basal serum TSH and PRL concentrations, diabetes insipidus, and evolving disease. Although full pituitary function assessment is mandatory to identify combined pituitary hormone deficiencies, a TRH test is not essential, and the diagnosis should be made by serial T(4) measurements.

The role of 123I-diagnostic imaging in the follow-up of patients with differentiated thyroid carcinoma as compared to 131I-scanning: avoidance of negative therapeutic uptake due to stunning

OBJECTIVE

Some patients with relapsed differentiated thyroid cancer may show rising thyroglobulin (Tg) levels despite a lack of 131I uptake on routine whole body imaging. A significant proportion of these patients, after therapy doses of 131I, may demonstrate positive 131I uptake with a subsequent fall in serum Tg, implying a therapeutic effect. Attempts to identify such patients by increasing the dose of the diagnostic 131I tracer may lead to inhibition of subsequent uptake after the therapy dose, an effect referred to as 'stunning' and associated with a reduction in therapeutic effect. 123I is a short half-life gamma-emitter, thought to be unlikely to cause stunning, which may thus be more suitable than 131I for diagnostic imaging of thyroid cancer.

DESIGN AND PATIENTS

The efficacy of the 123I radionuclide was determined in a longitudinal study of 12 patients who were selected only because they showed elevated serum Tg and a negative diagnostic 131I whole body study prior to therapy with 131I.

RESULTS

There was almost complete concordance in uptake between 123I diagnostic imaging and the final scans carried out after 131I therapy (hereafter known as therapy studies) in 11 out of 12 patients at their first evaluation, in each of four patients receiving 123I at their second evaluation and in a single patient receiving 123I at a third evaluation. One patient had a positive 123I study but a negative 131I therapy study: following therapy Tg declined from 5.5 pg/l to undetectable levels, implying a therapeutic effect, and suggesting that the negative uptake was not the result of stunning. Two negative diagnostic 123I studies were followed by negative therapy studies, and thus there were no false negatives. 123I correctly identified disease in the nine patients with metastases in the lungs, mediastinum and bone at the first evaluation, in all four patients at the second evaluation and in the single patient at the third evaluation. At the end of the study, patients had received up to three 131I therapy doses, Tg had risen in four patients, fallen in eight and become undetectable in one patient.

CONCLUSIONS

123I is highly sensitive in diagnosing local recurrence and metastatic disease, and produces scintigraphic images which concord well with uptake following 131I therapy. It is proposed that 123I imaging, in combination with serum Tg measurements, should replace 131I tracer imaging as an indicator of the potential efficacy of 131I therapy. Stunning, with its detrimental effects on 131I therapy, may thus be avoided. The possibility of false negative images due to the stunning phenomenon must always be borne in mind if there is a discrepancy between positive 131I imaging studies and a surprisingly negative subsequent 131I therapy scan.

[Thyroid function tests in viral chronic hepatitis]

BACKGROUND

One hundred and twenty five patients with virus B or C chronic active hepatitis and postnecrotic cirrhosis and different degrees of liver dysfunction were studied.

AIM

1) To determine a thyroid hormonal profile; 2) to evaluate the prognostic value of these tests in relation to the progression of the disease and mortality; 3) compare these findings with Child-Pugh classification.

PATIENTS AND METHODS

The patients were divided in four groups: a) 31 with chronic active hepatitis; b) 41 with postnecrotic cirrhosis Child A; c) 35 with postnecrotic cirrhosis Child B and d) 18 with postnecrotic cirrhosis Child C. The protocol comprised serum measurements of albumin and bilirrubin, estimates of prothrombin time and clinical evaluation of ascites and encephalopathy, measurement of total serum triiodothyronine, thyroxine, thyroid-stimulating hormone, free thyroxine, reverse triiosothyronine, calculated rT3/T3 index (IrT3) and thyrotropin-releasing hormone test.

RESULTS

Total serum triiodothyromnine showed the most significant difference among the groups, gradually lower as the disease became more advanced (CAH: 149.2 +/- 42.3 ng/dL; PNC-A: 137.4 +/- 37.2 ng/dL; PNC-B: 88.0 +/- 28.4 ng/dL and PNC-C: 41.8 +/- 21.9 ng/dL). Low levels of T4 (4.5 +/- 2.0 micrograms/dL) and FT4 (0.7 +/- 0.4 ng/dL) and elevated levels of thyroid-stimulating hormone (7.2 +/- 11.5 microIU/mL), reverse triiosothyronine (60.8 +/- 52.1 ng/dL) and calculated rT3/T3 index (2.2 +/- 2.6) were more frequent in patients with postnecrotic cirrhosis Child C. Thyrotropin-releasing hormone test was normal in the majority of the patients.

CONCLUSION

The present study shows a positive relationship between the low serum levels of T3 and elevated serum levels of rT3 and IrT3/T3 with the degree of hepatic dysfunction according to the Child-Pugh classification.

Diurnal thyrotropin secretion in short-term profound primary hypothyroidism: does it ever persist?

Circulating serum thyrotropin (TSH) levels in euthyroid humans show a definite circadian variation, which is maintained in both mild hyperthyroidism and mild hypothyroidism. Yet conflicting data exist with regard to whether this variation persists in at least some patients with severe primary hypothyroidism. We, therefore, studied the diurnal variation in serum TSH in 10 patients (age range 20 to 84 years) with a history of thyroid failure due to prior total thyroidectomy and radioiodine (RAI) ablative treatment performed for thyroid cancer after short-term discontinuation of thyroid hormone (TH) therapy. Serum TSH was measured hourly for a 24-hour period. All data were normalized by converting the TSH values to a percentage (%), designating the 11:00 hour value as 100% (baseline). The average serum TSH levels were markedly elevated in all patients. There was no statistically significant difference between the TSH % values at any time during the 24-hour period when compared with baseline. Further, cosine regression analysis showed absence of rhythmicity in TSH % values over time; notably, no patient showed a variation in TSH % values > or = 15% of baseline. In conclusion, diurnal rhythmicity in serum TSH levels was abolished in a uniform cohort of patients with short-term severe primary hypothyroidism. We speculate that the complete lack of peripheral negative feedback input to the hypothalamus or pituitary or both may override the central rhythm-sustaining influences on TSH secretion.

Influence of age and sex in modulating TSH level in primary hypothyroidism

Previous studies addressing the interaction of age and sex with the function of the hypothalamic-pituitary-thyrotrophs axis yielded conflicting results, due in part to inability to control for the effect of variable free thyroid hormone levels. We studied the effect of age and sex on TSH levels in patients with severe primary hypothyroidism who have essentially undetectable plasma thyroid hormone levels. The TSH levels were measured in 116 thyroid cancer patients four weeks after the withdrawal of thyroxine therapy in preparation for radioidine scan/treatment. All patients has a TSH >/= 30 mU/L (normal = 0.2-5) and a free T4 < pmol/L (normal = 10-25). Thirty males and 86 females with a mean age (+/- SD) of 40 +/- 16 (range 6-89 years) were studied on up to four hypothyroid episodes, with a total of 191 episodes. The TSH level during the first hypothyroid episode correlated significantly with the TSH level during subsequent episodes (first episode versus second episode, r = 0.7, P = 0.0001; first versus third episode, r = 0.6, P = 0.03). There was a significant negative correlation between age and TSH level (r = -0.24, P = 0.0009) that persisted when only the first hypothyroid episode was considered (r = -0.23, P = 0.01), or when only males (r = -0.32, P = 0.02) or only females (r = -0.23, P = 0.005) were considered. Means of TSH levels in males and females were not significantly different (130 verus 114 mU/L, respectively; P = 0.28). We conclude that age but not sex may modulate the sensitivity/responsiveness of the hypothalamic-pituitary thyrotroph axis to primary hypothyroidism.

Rapeseed products from double-low cultivars as feed for dairy cows: effects of long-term feeding on thyroid function, fertility and animal health

Eighty-five dairy cows of the Swedish Red and White Breed (SRB) were included in a long-term experiment during 3 consecutive lactations. The cows were divided into 3 different dietary groups that received no rapeseed (NR), up to 1.2 kg dry matter (DM) 00-rapeseed meal plus 0.2 kg DM full-fat 00-rapeseed (MR), and up to 2.5 kg DM 00-rapeseed meal plus 0.9 kg DM full-fat 00-rapeseed (HR) per day. No significant differences in culling rates or disease rates were found between the feeding groups at any time during the experiment. The interval from calving to conception among the primiparous cows was longer for the HR-group (125 days) than for the NR-group (100 days). The response to a thyrotroph releasing hormone around 90 days postpartum during the first lactation was significantly higher for the HR-group (86.7 mu/L/h) than for the NR-group (55.2 micrograms/L/h). This indicates that at the highest level of rapeseed feeding, glucosinolates had a very mild, suppressive influence on thyroid hormone release, apparently compensated for by an increased activity along the hypothalamic-pituitary-thyroid axis. No significant differences in fertility or thyroid function were found among the pluriparous cows. During 2nd lactation the concentration of serum urea was higher in the NR-group (7.31 mmol/L) than in the HR-group (6.83 mol/L). The effects of independent environmental factors influenced fertility and thyroid function to a much greater extent than the rapeseed feeding. It was concluded that the feeding of rapeseed products from certified double low varieties of B. napus to adult dairy cows in amounts up to 3 kg rapeseed meal per cow and day would not have any negative effects on animal health or fertility.

Cardiopulmonary bypass and thyroid hormone metabolism

Early investigations involving patient response to thyrotropin-releasing hormone during cardiac operations prompted researchers to consider that the cardiopulmonary bypass (CPB) procedure may affect this response. Results from several studies indicate that total T3 (active thyroid hormone) concentrations are significantly reduced during and after CPB (ie, the euthyroid sick syndrome). Inhibition of the monodeiodinase pathway during CPB, and subsequent inhibition of peripheral thyroxine to T3 conversion may partly explain these findings. These data prompted the investigation of intravenous T3 administration to patients undergoing CPB. Clinical trials to date have shown that intravenous T3 administered during or after CPB improves cardiac output and contractility. This article reviews the studies of thyroid hormone before, during, and after CPB operations.

Are patients with low serum thyroid stimulating hormone and normal total thyroxine hyperthyroid? Usefulness of 99mTc pertechnetate uptake

The records of 107 patients who had had thyroid 99m Tc pertechnetate uptake measured, were reviewed. In patients with normal serum thyroxine (T4) and thyroid stimulating hormone (TSH), 35 of 36 with normal uptake and three with high uptake were clinically euthyroid. In patients with high serum T4 and low TSH, seven had normal and 29 had high uptake and all were clinically hyperthyroid. In patients with normal serum T4 and low TSH, 10 of 11 with high uptake were clinically hyperthyroid whereas only two of 18 with normal uptake were. The sensitivity, specificity and positive predictive value of pertechnetate uptake measurements were 83%, 94%, and 91%, respectively. The measurement of pertechnetate uptake is a rapid investigation and may help in the interpretation of patients with undetectable serum TSH found in the presence of normal serum T4.

Is idiopathic atrial fibrillation caused by occult thyrotoxicosis? A study of one hundred consecutive patients with atrial fibrillation

In this study we evaluated the possible relationship between idiopathic atrial fibrillation and occult thyrotoxicosis, diagnosed by lack of response of thyroid stimulating hormone to administration of thyrotropin releasing hormone. Three groups were compared: 25 patients with idiopathic atrial fibrillation; 52 with cardiovascular atrial fibrillation; and 27 with sinus rhythm. Patients were excluded with any clinical evidence of thyrotoxicosis or with elevated serum FT4 level, as well as those with diseases or on medications known to be associated with a diminished response to administration of the releasing hormone. A flat test (lack of response) was found in only 4% of the patients. There was no significant difference among the 3 groups. Based on these data we believe that there is no relationship between idiopathic atrial fibrillation or any other type of atrial fibrillation and occult thyrotoxicosis.

Gender differences in TRH-stimulated TSH and prolactin in primary degenerative dementia and elderly controls

We performed thyrotropin-releasing hormone (TRH) stimulation testing in 18 nondepressed patients with primary degenerative dementia (10 M, 8F; average age +/- SD = 68 +/- 7) and 12 elderly controls (7M, 5F; average age +/- SD = 61 +/- 6). Six patients were retested approximately 2 years later. Initial Mini-Mental State Examination scores for patients ranged from 2 to 28 (average +/- SD = 18 +/- 6) and the scores for the control subjects were all equal to 30. Protirelin (500 micrograms) was injected iv and blood was sampled at 0, 15, 30, 45, 60, and 90 min for thyrotropin-stimulating hormone (TSH) and prolactin (PRL). There were no significant differences between patients and controls in baseline T4, T3 uptake, TSH, or PRL. No significant differences were found between patients and controls for either TRH-stimulated TSH or PRL at all time points. Duration of illness, severity of dementia, and severity of depressive symptoms did not correlate significantly with stimulation test results. There were, however, significantly greater responses in stimulated TSH and PRL for women compared with men in both patients and controls. Upon repeat testing (n = 6), TRH-stimulated TSH and PRL were not significantly different from the initial results.

A new TSH assay. Just another technique or a useful test?

The immunoradiometric assay is a sensitive test for diagnosing thyroid dysfunction. It permits greater accuracy by measuring response of thyrotropin-producing cells of the pituitary to thyroxine (T4) as opposed to comparing circulating T4 to a range of values from healthy controls. The assay allows improved precision in establishing replacement and suppressive doses of hormone for thyroid disease.

Low serum TSH with normal total thyroid hormone levels: an indicator of free T4 excess

We have studied 18 patients with low serum thyrotrophin (TSH) levels accompanied by normal thyroxine (T4) and triiodothyronine (T3) levels in order to clarify whether or not they are thyrotoxic. Serum T4, T3, free T3, free T4 and TSH were estimated three times weekly for 3-4 weeks. Thyroxine binding globulin (TBG) levels were estimated on one occasion only. Thyroid hormone data were expressed as the cumulative probability of having at least one result above the relevant normal range by the nth sample (Pn). For free T4 this probability was 61% by the 10th sample. Free T4 values were confined to the upper half of the normal range or above throughout the study. In contrast, free T3 values were distributed evenly within the normal range (P10 = 12%). For total T4 and total T3, P10 was 34 and 11% respectively. Thus, subjects with subnormal TSH levels but normal T4 and T3 levels have been shown to have elevated serum free T4 levels, an indicator of biochemical hyperthyroidism.

Thyroid dysfunction and hypercholesterolaemia in the general population of Glasgow, Scotland

As part of a screening programme for coronary heart disease risk factors, fasting plasma cholesterol was measured in 2,250 people from the east-end of Glasgow. Plasma thyrotropin (TSH) was measured in the 90 individuals (4% of the population studied) who had a cholesterol level greater than or equal to 8.0 mmol/l. Four had unequivocal biochemical evidence of hypothyroidism-TSH greater than 34 mU/l and a low plasma thyroxine (T4) less than or equal to 45 nmol/l. A further 8 were found to have raised TSH levels suggesting they may have subclinical hypothyroidism. These data indicate that thyroid dysfunction may make a significant contribution to hypercholesterolaemia in the general population.

Non-adenomatous inappropriate TSH hypersecretion and euthyroidism requires no treatment

The syndrome of inappropriate TSH secretion is described in a euthyroid girl and her father. Based on nuclear T3 binding studies in fibroblasts, generalized tissue resistance was associated with a lower binding affinity for T3 in nuclear extracts suggestive of a structurally abnormal receptor for T3. Early recognition of the syndrome and observation of the short-term response to thyroid medication prevented unnecessary trials of antithyroid medication and later radical ablative thyroid treatment.

Generalised peripheral nerve dysfunction in acromegaly: a study by conventional and novel neurophysiological techniques

Twenty four patients with clinical, radiological and biochemical evidence of acromegaly were investigated by a number of independent neurophysiological tests. Two-thirds of the patients showed evidence of generalised peripheral nerve dysfunction. A significant correlation was found between total exchangeable body sodium, an indicator of disease activity, and the severity of the neuropathy. The generalised peripheral nerve abnormality was found to occur independently of the associated carbohydrate intolerance human growth hormone levels and other endocrinological dysfunction in this disorder.

Impaired thyrotrophin secretion following the administration of thyrotrophin-releasing hormone in type II diabetes mellitus

Serum thyrotrophin has been measured before and after the intravenous administration of 200 micrograms of thyrotrophin-releasing hormone in 91 white subjects (33 stable diabetic patients and 58 healthy controls), none of whom had any clinical evidence of thyroid or pituitary dysfunction. Seven of the diabetic subjects failed to achieve a rise of serum thyrotrophin of greater than 2 mU/l above basal concentrations, as compared with only one of the control subjects (P = 0.006). The difference in response between diabetics and controls was confined to patients with Type II (non-insulin-dependent) diabetes: thus 5 of 13 Type II patients and 2 of 20 Type I (insulin-dependent) patients failed to show a normal response to thyrotrophin releasing hormone injection. No significant effect of glycaemic control on thyrotrophin responses was noted. These results suggest that Type II diabetes mellitus may be a cause of impaired thyrotrophin secretion in patients with no clinical evidence of pituitary disease. The mechanism for this impaired pituitary hormone release remains to be clarified.

Twenty-four-hour serum levels of T4 and T3 in relation to decreased TSH serum levels and decreased TSH response to TRH in affective disorders

The serum levels of thyroxine and triiodothyronine (T4 and T3) were investigated at 10 different time points during a 24 h period in 31 inpatients meeting the RDC criteria for acute major depressive disorder. Twenty-three of these patients were also reinvestigated in a state of partial or complete remission. The results show that there was no significant difference in T4 or T3 levels during the 24 h period between depressed patients and 32 healthy controls despite significantly decreased TSH levels and TSH response to TRH administration (delta TSH) in the patient group. No indications were obtained that the patients' clinical presentation or depressive symptomatology as revealed by their CPRS scores, psychotropic medication, melatonin levels, or the outcome of the dexamethasone test, significantly influenced the T4 or T3 levels. The depressed patients who were studied longitudinally showed increased T4 levels in the acute phase compared to remission, whereas the T3 levels did not change. However, the levels of thyroid hormones were within the normal range in the acute phase as well as in remission. Furthermore, the changes in thyroid hormones between the state of relapse and remission were not significantly correlated to the corresponding increase in TSH levels and delta TSH between the two assessments. The present results are consistent with the hypothesis that the mechanism behind the impaired TSH response to TRH in acute major depressive disorder is a downregulation of the pituitary TRH receptors.

Free thyroid hormone levels and TSH response to TRH in patients with autonomous thyroid adenomata and normal T3 and T4

Free thyroid hormone levels together with basal and TRH stimulated TSH levels, have been determined in 50 patients with autonomous thyroid adenomata, who had normal serum total T3 and T4 values. Similar measurements were made in 33 healthy subjects. FT3 and FT4 plasma levels were significantly higher (P less than 0.01 and P less than 0.05 respectively), and basal and TRH stimulated TSH were significantly lower (P less than 0.05 and P less than 0.001 respectively) in the patients than in the controls. The TSH response to TRH was decreased in spite of normal free thyroid hormones in 25 patients and in a further ten both the delta TSH after TRH and the free fractions were normal. Eighteen patients were studied over periods from 4 37 months by repeating thyroid hormone levels and TRH tests. In six of them a change of these parameters toward toxicity was observed. The data obtained in the longitudinal study indicate that the values of free thyroid hormones and the result of the TRH test obtained by a single determination may represent different steps in the evolution of autonomous thyroid adenomata rather than a distinct pathophysiological condition.

[Thyroid hormones in women with liver cirrhosis]

Basal thyroid hormone levels were measured in 68 women with liver cirrhosis (LC) of different etiology (alcoholic n = 34, posthepatitic B n = 9, PBC n = 5, cryptogenetic n = 18, M. Wilson n = 2). In addition the rise of TSH after 400 micrograms TRH was measured in 23 women with LC and compared with the data obtained from 17 women of a control group. There was no difference of the median T4-concentrations (LC 8.0 micrograms/dl versus 7.2 micrograms/dl) but a significant correlation of T4 to the grade of decompensation of LC. In contrast of T4 there was a marked decrease of T3 in LC-patients (109 ng/dl versus 143 ng/dl) and a rise of reverse T3 (0.21 ng/ml versus 0.13 ng/ml). The decrease of T3 and rise of reverse T3 equally correlated to the severeness of LC. TBG concentrations fell according to the grade of decompensation of LC and T4/TBG-quotient exhibited no difference to the control data (0.51 both). Though basal thyroid hormones and TSH show euthyroidism the significant augmented TSH release after TRH (delta-TSH 7.0 versus 3.2 microU/ml) indicate a status of latent hypothyroidism. In alcoholic cirrhosis the degree of TSH release was much higher than in non alcoholic cirrhosis. Estradiol and estrone levels correlated significantly negatively to T4, T3, estrone negatively to TBG and positively to reverse T3 but not to TSH and TSH release. Otherwise TSH release correlated positively to estradiol. The thyroid status in women with liver cirrhosis does not differ from the thyroid hormone profile found in men with cirrhosis.

Exaggerated responsiveness to thyrotrophin releasing hormone: a risk factor in women with coronary artery disease

Thyroid function tests were performed and thyroid antibodies and serum cholesterol concentrations measured in 12 women aged 60 years or under with severe coronary artery disease proved by coronary angiography. This group was compared with 11 women with normal coronary angiography. Ten out of the 12 women with coronary artery disease had an exaggerated response of thyroid stimulating hormone to thyrotrophin releasing hormone compared with two out of 11 controls (p less than 0.008). The mean serum cholesterol concentration was significantly higher in those with coronary artery disease than in the controls. Thyroid antibodies were present in four of those with coronary artery disease and one of the controls. There was no difference in the risk factors for coronary artery disease between the two groups except for cigarette smoking. Eleven out of 12 in the coronary artery disease group smoked cigarettes compared with four out of 11 in the control group (p less than 0.01). Minimal impairment of thyroid function is an important risk factor for coronary artery disease in women.

The screening of patients with suspected thyrotoxicosis using a sensitive TSH radioimmunoassay

A radioimmunoassay was optimized to measure serum TSH with maximum sensitivity (sTSH). With this assay sTSH was less than 0.5 mIU/l in 100% of 64 patients with proven thyrotoxicosis and greater than 0.5 mIU/l in 92% of 76 normal subjects. sTSH correctly predicted the TSH response to TRH (delta TSH) in 93% of 125 patients with suspected thyrotoxicosis. In this group thyrotoxicosis was excluded by an sTSH greater than 0.5 mIU/l in 52% of patients thus avoiding the need for further testing.

Intranasal thyrotrophin releasing hormone is a potent stimulus for TSH release in man (comparison with intravenous and oral TRH)

Intranasally administered TRH was tested and compared to i.v. and oral TRH in respect to its efficacy of TSH stimulation and thereby the stimulation of thyroid reserve. TSH release after nasal application is as prompt as after the i.v. route, reaching a peak at 20 to 30 min. After that, however, compared to the i.v. administration its stimulatory effect is prolonged, lasting over 3 h. At the dose used in this study the peak TSH response after intranasal TRH administration was 14.7 +/- 1.6 mU/l compared to 8.4 +/- 1.4 and 23.1 +/- 4.4 mU/l after i.v. and oral administration respectively (P less than 0.005). Intranasal application of TRH is as potent as i.v. or oral TRH for the stimulation of thyroid reserve. At 3 h a marked increase of T3 and a smaller elevation of FT4 is observed (delta T3 = 48.4%, delta FT4 = 31.6%). The nasal peptide was well tolerated locally and systemic side effects were comparable to those of i.v. TRH. This form of application offers a practical advantage by avoiding intravenous injections. Its diagnostic potential in investigation of thyroid disease and its possible therapeutic application have yet to be elucidated.

Comparative study of intravenous, nasal, oral and buccal TRH administration among healthy subjects

Four different modes of TRH application (400 micrograms iv, 1 mg nasal, 10 mg buccal and 40 mg oral) were investigated in young healthy subjects for evaluation of thyrotropin (TSH) and prolactin (PRL) stimulation. Plasma TSH, PRL, T4, T3, thyroxine-binding-globulin (TBG) were measured by radioimmunoassay. There were significant increases of TSH and PRL following TRH stimulation by all test forms. Bolus injection of TRH led to maximal TSH and PRL plasma levels within 20 min to 30 min, compared with 30 min to 45 min following nasal administration. Buccal and oral application produced more prolonged TSH and PRL increases, achieving plateau levels after 120 min to 180 min. Stimulated PRL levels were higher in women than in men. Uniformity of PRL response was better after iv or nasal than buccal and oral TRH stimulation. Known side effects were lower after nasal than iv TRH application. Buccal and oral administration provoked no side effects. Nasal TRH application seems to be a well suited test form for TSH and PRL stimulation.

A prospective study of the effects of lithium on thyroid function and on the prevalence of antithyroid antibodies

Tests of thyroid function and pathology were carried out on 133 patients before they were treated with lithium (Li+). Of the 12 patients who subsequently became hypothyroid during treatment with lithium 9 had, before the commencement of treatment, thyroid autoantibodies and/or an exaggerated thyroid stimulating hormone (TSH) response to thyrotropin releasing hormone (TRH), whereas 3 patients had neither of these indicators. Lithium administration was accompanied by a rise in thyroid antibody titre in 20 patients but a fall in only 5, a statistically significant difference. Evidence that it may be an immunostimulant is discussed. Li+-induced thyroid failure cannot be accurately predicted, and may occur suddenly. The best minimum safeguard, therefore, is serial thyroxine (T4) (or free T4) estimation, supplemented if equivocal by a free thyroxine index (FTI), a basal TSH and, if doubt remains, by a TRH test.

Antithyroid drugs

Over the past four decades, a great deal has been learned about the pharmacology and mechanisms of action of antithyroid drugs. Their ability to inhibit hormone biosynthesis involves complex interactions with thyroid peroxidase and thyroglobulin, many of which are still poorly understood. Their spectrum of activity is much wider than previously thought, and a number of clinically important extrathyroidal actions have been identified. Despite a greater appreciation for the intricacies of antithyroid-drug pharmacology, controversies still surround the use of these agents in the treatment of thyrotoxicosis. These controversies are apt to continue until the pathophysiology of Graves' disease is fully elucidated.

The effect of oestrogen (mestranol) on the thyrotrophin response to thyrotrophin releasing hormone in postmenopausal oophorectomised women

The thyrotrophin (TSH) responses to thyrotrophin releasing hormone (TRH) in 16 oophorectomised postmenopausal women on long term treatment with mestranol 24 micrograms daily were compared to those in 16 oophorectomised postmenopausal women on placebo treatment. No significant difference between the groups was found in either basal TSH levels or the TSH response to TRH. It is therefore unlikely that the difference in TSH response to TRH between men and women of reproductive age is due to a direct stimulatory effect of oestrogen in women.

Occult thyrotoxicosis in patients with chronic and paroxysmal isolated atrial fibrillation

Thyroid function tests, including thyrotropin releasing hormone administration (TRH), were performed in 40 consecutive patients with isolated atrial fibrillation (IAF) (i.e., without any other evidence of cardiac disease). The arrhythmia was chronic in 5 and paroxysmal in 35 patients. Thyrotoxicosis could not be diagnosed either clinically or by abnormal serum levels of T4, T3, T3 BC, and thyroid stimulating hormone (TSH). Thyroid stimulating hormone response to TRH, which was normal in 35 patients, was absent in 5 (12.5%) who were considered to have occult thyrotoxicosis. One had chronic and the other 4 had paroxysmal IAF. The arrhythmia did not recur after antithyroid treatment in these four patients who were in sinus rhythm after a mean follow-up period of 21 months. Full exploration of the thyroid function therefore seems useful not only in patients with chronic IAF, but also in those affected by the paroxysmal form.

Radioimmunoassay of human thyrotropin: analytical and clinical developments

Recent modifications of the radioimmunoassay systems for TSH have greatly extended the clinical utility of the measurement of this hormone, so that its use is no longer limited to the diagnosis of primary hypothyroidism. The newer assays provide improved sensitivity and specificity, such that it is now possible to distinguish TSH levels that are within the normal range from those that are suppressed, e.g., in thyrotoxicosis. New vistas of clinical applications are being revealed as we improve our understanding of human thyroid physiology and pathophysiology. It is the purpose of this communication to summarize information about the improved TSH radioimmunoassay, to demonstrate the new observations available regarding TSH concentrations in various normal and diseased conditions, and finally, to illustrate the various ways in which the assay provides more accurate guidance in the clinical diagnosis and management of thyroid and nonthyroid disease.

The role of thyrotrophin releasing hormone in the diagnosis of isolated gonadotrophin deficiency

We studied the response of PRL and TSH to thyrotrophin-releasing hormone (TRH) in 15 boys with delayed adolescence and 6 male subjects with isolated gonadotrophin deficiency (IGD). TRH tests were repeated in the IGD subjects during and 1 month following hCG treatment. Male IGD subjects showed a significantly decreased basal and TRH induced PRL response compared to male controls and subjects with delayed adolescence. Human chorionic gonadotrophin (HCG) treatment of male IGD subjects restored basal and stimulated PRL levels to the range of normal controls. This was, presumably, an estrogenic effect since non aromatizable androgens did not increase the PRL response; moreover, the antioestrogen, clomiphene, decreased the PRL response when given with HCG. The TSH response to TRH in delayed adolescents was increased as compared to adult male controls and IGD subjects and was similar to adult female controls. HCG treatment of IGD subjects had no effect on basal nor peak TSH levels, although ethinyl oestradiol did increase the TSH response in two IGD subjects. These studies show that the PRL and TSH responses to TRH may differentiate delayed adolescence from IGD. The increased TSH response to TRH in delayed adolescence as compared to adult males, is a manifestation of an enhanced oestrogen effect in these patients. The abnormal PRL dynamics in IGD is a consequence of estrogen deficiency.

Mild hypothyroidism and oedema: evidence for increased capillary permeability to protein

Nine female patients with normal serum total thyroxine (T4) and triiodothyronine (T3) but elevated thyroid stimulating hormone (TSH) levels were studied. Six patients had generalised oedema associated with maximal diurnal weight gains in excess of 1.4 kg. Under conditions of forced water diuresis, before and during physiological replacement of 1-thyroxine, the supine transcapillary escape rate of albumin (TERA) was measured, while the venous colloid osmotic pressure (COP), packed cell volume (PCV) and urinary excretion of water and electrolytes were studied in both the supine and upright positions. The TERA, diurnal weight gain and orthostatic increase in COP fell significantly with treatment. In the six patients with oedema and excessive diurnal weight gains, the retention of salt and water on tilting was reduced with thyroxine treatment. In female patients we consider generalised oedema associated with excessive diurnal weight gain, to be a common and early symptom of hypothyroidism, meriting thyroxine replacement therapy.

The prevalence of thyroid dysfunction in mentally handicapped in-patients

A survey was made of the thyroid function of 402 mentally handicapped patients in a long-stay hospital and its satellite units. The prevalence of hypothyroidism in a 2-year period was 25/402 (6.2%), and 17/364 (4.7%) when people with Down's syndrome were excluded. Hyperthyroidism was found in 3/402 (0.7%). These results include 16 patients with hypothyroidism, and two with hyperthyroidism, who were newly detected during the surgery. With diagnosis, treatment was started. This occurrence of thyroid disorders is higher than in both the general population in the community and also in other psychiatric in-patients. Biochemical investigation is essential as the disorders are difficult to detect clinically, and untreated the patients are liable to the complications of hypothyroidism and hyperthyroidism.