Failure of triiodothyronine to inhibit TSH-mediated thyroid hormone release in man

We studied the effect of short-term triiodothyronine administration on thyroid gland responsivity to exogenous thyrotropin in four euthyroid human subjects. Thyroidal iodine release and serum thyroxine during daily im injections of bovine TSH were not significantly inhibited, despite a four-fold elevation in serum T3 concentrations. This negative finding contrasts with earlier positive reports of a regulatory "short-loop" effect of elevated circulating T3 on the thyroid gland. This difference may be due either to the use in previous murine or in vitro studies of non-physiologic, high doses of exogenous T3, or failure to control the withdrawal of the trophic effect of endogenous TSH in man on the subsequent glandular response.     

Prognostic indicators for toxic mastitis in dairy cows

OBJECTIVE: To measure serum thyrotropin (TSH), and free thyroxine concentrations in newborns delivered in areas with differing degrees of iodine deficiency, (prior to the salt iodization programme), and to use these biochemical indices to assess the current status of thyroid function in the group. DESIGN: Cross sectional. SETTING: Chemical Pathology, University of Zimbabwe, Medical School. Radio-immunoassay laboratory, Parirenyatwa Hospital. SUBJECTS: 500 healthy full term newborns, aged two to four days old, weighing not less than 2.5 kg. MAIN OUTCOME MEASURES: Thyroid hormone status of newborns. RESULTS: The mean serum FT4 level was found to be slightly but significantly different between the newborns from Harare region, (low goitre prevalent area), and Wedza district (moderate to severe goitre prevalent area). Although there was a trend in the distribution of TSH to higher values in the moderate to severe goitre prevalent areas, the differences were statistically non significant, p = 0.175. The median TSH value in the newborns was 4 microU/ml. TSH values were below 10 microU/ml in 90%, between 10.1 and 20 microU/ml in 9%, and between 20.1 and 32 microU/ml in 1% of the cases. No sex related differences were observed in either the TSH nor the FT4 values of the newborns. CONCLUSION: This study demonstrates that the iodine supplementation programme has been successful, but further monitoring is necessary to ensure complete supplementation throughout the country and to guard against hyperthyroidism which is known to occur during iodine supplementation programmes.     

Thyroglobulin assay in the follow-up of patients with differentiated thyroid carcinomas: comparison of its value in patients with or without normal residual tissue

The usefulness of serum thyroglobulin (Tg) assay in the follow-up of differentiated thyroid carcinomas has been evaluated in 109 subjects divided into two groups. Group 1 included 64 patients who had undergone total thyroid ablation. In 40 of the 41 patients in complete remission serum Tg was undetectable during replacement therapy (TSH below 5 microunits/ml). In 18 out of the 40 patients serum TG was detectable following endogenous TSH stimulation. As 83% of these patients had ectopic uptake prior to the last radioiodine treatment, this release of Tg under TSH stimulation suggests the persistence of occult neoplastic tissue. Of the other 23 patients, 20 had bone or lung metastases and 3 patients had lymph node recurrences: in all these patients, serum Tg was detectable during replacement therapy and increased after TSH stimulation. Group 2 included 45 patients in whom normal residual thyroid tissue was present at the time of the investigation. Of these, 35 patients were in apparent remission and 19 of them had detectable Tg level within the normal range. The other 10 patients had detectable metastases and in 4 of these the Tg level was also within the normal range. Thus, no conclusion can be drawn from a normal Tg level in the presence of residual thyroid tissue. Bovine TSH stimulation did not improve significantly the diagnostic value of Tg assay in this group of patients.     

A study of thyroid disease in family practice

Thyroid disease is relatively common in family practice, yet is often undiagnosed or poorly managed. This study examines several aspects of thyroid disease in a large, semirural family practice setting and exemplifies the type of practical clinical research that can be done in family medicine. An overall prevalence of approximately one percent was determined for thyroid disease in this practice. In a series of 85 patients, the ratio of hypothyroidism:hyperthyroidism:euthyroid goiter was 9:2:1 respectively. Initial signs and symptoms recorded for these patients conformed closely to the findings in other large series. Eighty percent of the patients with idiopathic hypothyroidism never had enlarged glands, whereas 100 percent of the patients with hypothyroidism associated with Hashimoto's thyroiditis had enlarged glands. Laboratory aids such as serum thyroid stimulating hormone (TSH), anti-thyroid antibodies, and radioactive iodine uptake (RAIU) and scans were inadequately utilized. Medical and/or surgical consultation was obtained in 17.5 percent of patients with hypothyroidism, 80 percent of patients with hyperthyroidism, and 63 percent of those with euthyroid goiter. Currently 95 percent of the hypothyroid patients and 100 percent of the hyperthyroid patients are euthyroid.     

Neonatal transient hypothyroidism: aetiological study. Italian Collaborative Study on Transient Hypothyroidism

AIMS: To define the aetiology of neonatal transient hypothyroidism (NTH) and recommend preventive measures. METHODS: Maternal and perinatal clinical data on the use of antiseptics, drugs, and contrast agents containing iodine were collected from 40 subjects. Thyroid stimulating hormone (TSH), free thyroxine (FT4), thyroxine (T4), thyroglobulin (TG), TSH receptor antibodies, thyroid peroxidase antibodies and urinary iodine were measured in random neonatal samples. In the mothers with known or suspected thyroid disorders, TSH, FT4, TSH receptor antibodies and thyroid peroxidase antibodies were also measured. RESULTS: The NTH aetiology was identified in 85% of cases. More than 50% of the babies with transient hypothyroidism had been exposed to iodine; maternal transfer of antibodies had occurred in a third of them. CONCLUSIONS: It is suggested that the practice of using iodine containing disinfectants should be withdrawn, and chlorhexidine substituted instead; that pregnant women should be advised of the adverse effects of using iodine products; and that thyroid function should be monitored whenever iodine is used.     

Changes in thyroid hormone levels during growth hormone therapy in initially euthyroid patients: lack of need for thyroxine supplementation

The occurrence of central hypothyroidism in previously euthyroid children during GH therapy has been reported with widely varying incidence. We monitored the acute effects on the hypothalamic-pituitary-thyroid axis in 15 euthyroid children with classic GH deficiency during the first year of GH therapy. All were initially euthyroid, as assessed by normal baseline TSH, T4, free T4, and T3 levels and negative antithyroid antibodies. A thyroid profile (T4, free T4 index, T3, rT3, and TSH) was performed at baseline and 1, 3, 6, 9, and 12-15 months after GH therapy began; a TRH stimulation test was performed at baseline and after 1, 3, and 9 months of therapy. By 1 month, there were significant decreases in T4, free T4 index, and rT3, and significant increases in T3 and the T3/T4 ratio. The changes from baseline values were greatest at 1 month, were almost universal for all thyroid values, and showed a gradual return to baseline from 3-12 months. There were no clinical signs of hypothyroidism and no change in baseline or TRH-stimulated TSH levels or in cholesterol levels, and all patients grew at velocities expected for the treatment schedule. There is little evidence for the development of clinically significant hypothyroidism in the great majority of initially euthyroid patients after GH therapy is begun. T4 supplementation is seldom needed in such patients.     

Iodine induced thyroid disease

Although iodine prevents goiter, enlarged thyroid glands continue to be detected in subjects, especially children, in spite of adequate iodine ingestion. Iodine may cause goiter in susceptible individuals by inhibiting the organic binding of iodine as is seen in adult asthmatics, neonates born of iodine ingesting mothers and in subjects residing along the littoral of Japan. Myxedema, especially in treated Graves' disease and Hashimoto's disease, may also be precipitated by iodine. On the other hand, iodine given to euthyroid subjects in areas of endemic goiter and to subjects with nontoxic nodular goiter may induce thyrotoxicosis by disclosing diffuse autonomously functioning thyroid tissue. An indirect adverse effect of iodine upon the thyroid gland may be manifested by lymphocyte glandular infiltrates and chronic thyroiditis which were sparse or absent in thyroid glands removed from subjects living in iodine deficient areas before iodine prophylaxis and therapy. Not only has the incidence of thyroiditis increased, but the histologic and clinical distinctions between treated Graves' disease and chronic thyroiditis have become indistinct. Experimentally, chronic thyroiditis has been produced in animals following large doses of iodine. Accumulated evidence supports the concept that iodine contributes to the genesis of chronic thyroiditis.     

Individually dosed levothyroxine with 150 micrograms iodide versus 100 micrograms levothyroxine combined with 100 micrograms iodide. A randomized double-blind trial

BASIC PROBLEM AND OBJECTIVE: Intrathyroid deficiency and the influence of thyroid stimulating hormone (TSH) are the main pathogenetic factors in the development of endemic euthyroid goitre. Goitre reduction is achieved with either administration of levothyroxine, which diminishes hypophyseal TSG production, or of iodide. Aim of this study was to compare the efficacy of treatment with a dose-fixed combination of levothyroxine plus iodide with that of an individualized dosage of levothyroxine plus iodide. PATIENTS AND METHODS: After randomization 49 patients with euthyroid goitre (24 women, 25 men, aged 20-43 years) were treated for 12 weeks in a double-blind trial. Patients in group A received levothyroxine in a weight-adapted dosage (75,100 or 150 micrograms) plus 150 micrograms iodide, while those in group B were given a fixed dosage of 100 micrograms levothyroxine plus 100 micrograms iodide. Basal TSH, thyroid hormones, iodide excretion, hyperthyroid score and sonographic volume of the thyroid were determined before treatment and after 12 weeks. RESULTS: Basal TSH levels were reduced in both groups (P < 0.0001), without significant difference between the two groups (median relative change: group A 78.1%, group B 52.8%). Thyroid volume was decreased independently of the form of treatment (P < 0.0001) (median relative reduction: group A 37.6%, group B 30.9%; difference not significant). Iodide excretion rose in both groups, without significant difference (group A 107%, group B 49%). There was hardly any change of the hyperthyroid score in both groups. There were no side effects. CONCLUSION: Both forms of medication were equally efficacious and well tolerated in the treatment of euthyroid goitre.     

Infantile and juvenile hypothyroidism with the gland in place and low radio-iodide uptake

27 hypothyroid infants of children, with a low iodine uptake in spite of a thyroid gland or thyroid tissue in normal pretracheal place, have been studied. 21 cases are related to primary thyroid involvement leading to vanishing iodine or technetium uptake. In 8 of these cases, clinical onset in late childhood, high frequency of antithyroid antibodies and of familial thyroid dysfunction were similar to those found in childhood's thyroiditis. 8 other cases had a precocious onset (first months in 6, first year in 1, second year in 1) with some pretracheal iodine uptake when first studied and no uptake at further examinations, 1 patient having received no treatment from first to second study, the others being without treatment from more than two months and certain of them receiving injections of TSH. The last 5 cases of this group were those of children born to 2 mothers with treated hypothyroidism, with low iodine uptake in pretracheal place. The role of genetic factors and auto-immunity in theses cases is discussed. The 6 other patients had clinically isolated hypothyroidism secondary to TSH deficiency, eventually associated to clinically inapparent GH or ACTH deficiencies, most of them by hypothalamic defect with normal response to TRH.     

Familial insensitivity of the pituitary and periphery to thyroid hormone: a case report in two generations and a review of the literature

A clinically euthyroid 2-yr-old girl was found to have diffuse goiter that measured 3 X 5.5 cm with a prominent systolic bruit. Serum free T4 (3.4 ng/dl) and serum T3 (360 ng/dl) remained elevated for the next 10 months even though she remained clinically euthyroid. Elevation of serum free T4 (3.0 ng/dl) and serum T3 (265 ng/dl) was also present in the 24-yr-old nongoitrous mother who had symptoms and signs of hypothyroidism. Following intravenous injection of TRH, basal TSH levels of 2.7 and 2.8 microunits/ml increased to peak values of 17 and 21 microunits/ml at 30 min in the daughter and mother, respectively. Administration of exogenous T3 followed by sequential testing with boluses of TRH revealed retention of TSH responsiveness in both daughter and mother during pretreatment with dosage regimens of T3 below 125 micrograms daily. Maintenance of TSH responsiveness to TRH in the presence of elevated levels of serum free T4 and serum T3 indicates relative pituitary insensitivity to thyroid hormone which could be overridden by increasing the circulating levels of serum T3 three to fivefold over the already elevated basal levels. The absence of clinical signs of thyrotoxicosis indicates peripheral insensitivity to thyroid hormone with elevated circulating concentrations presumptively compensating for the defect. Resistance to thyroid hormone in two generations of the same family suggests genetic inheritance, and is concordant with four earlier reports of familial aggregation in this syndrome.     

Thyroid gland function in neonates with transient hyperthyrotrophinemia from a region of slight iodine deficiency

The aim of this study was to evaluate thyroid gland function in neonates and babies with transient hyperthyrotrophinemia during the first twelve months of life in an attempt to establish the causes of this condition in neonates born in a region of slight iodine deficiency. Thirty-eight newborns were screened. Clinical observations and measurements of serum T3, T4, TSH levels as well as urinary iodine were conducted for one year (at the age of 2 weeks, 3-4 months, and after one year of life). The screened children showed significantly higher values of T4 (p < 0.001) in comparison with the reference value in successive follow-up examinations. High T4 values may result from an increased TBG concentration in serum, and its level should be determined in the analysed material. Other hormonal values normalized after the second weak of life. Iodine deficiency was found in 80% of the children. Our assessments concerning the causes of transient hyperthyrotrophinemia conform with previous findings. It was established that the most common causes are iodine deficiency and maternal thyroid disease. None of the screened children had goitre somatic anomalies or delayed psychomotoric development did not appear more frequently than in the general pediatric population.     

Changes in thyroid volume in response to radioactive iodine for Graves' hyperthyroidism correlated with activity of thyroid-stimulating antibody and treatment outcome

This study investigated 1) the relationship between thyroid volume and thyroid function in radioactive iodine (RAI) treatment for Graves' disease, and 2) the activity of thyroid-related Ig in serum on the responsiveness of thyroid tissue to RAI. The changes in thyroid volume per megabecquerel (MBq) of 131I retained in thyroid tissue was calculated by ultrasonography as a quantitative indicator of the effect of RAI on thyroid volume. Of the 52 patients treated with 131I (3.7 MBq retained/g thyroid tissue), 26 patients showed thyrotoxicosis, 20 patients became euthyroid, and 6 patients developed hypothyroidism 6 months after therapy. The change in thyroid volume per MBq 131I was lower (P < 0.01) in the hyperthyroid patients than in the euthyroid or hypothyroid patients. The activity of thyroid-stimulating antibody in serum immediately before the therapy was greater (P < 0.01) in the hyperthyroid patients than in the euthyroid patients and was greater (P < 0.05) in the euthyroid patients than in the hypothyroid patients; it was inversely correlated with the changes in thyroid volume per MBq 131I (r = -0.667; P < 0.01). Accurate measurement of changes in thyroid volume during the course of RAI treatment provides evidence of the responsiveness of Graves' disease thyroid tissue to RAI, which is related to the outcome of thyroid function. Thyroid-stimulating antibody determination may be useful in deciding the appropriate dose of RAI to obtain euthyroidism instead of hyperthyroidism.     

Long-term effect of 131I therapy of multinodular non-toxic goiter

The aim of this study was to investigate the long term effect of 131I treatment on thyroid function and size in patients with non-toxic multinodular goitre. The subjects were 69 consecutive patients with multinodular non-toxic goitre selected for 131I treatment and followed for a minimum of 12 months. Outcome measures were standard thyroid function variables and ultrasonically determined thyroid volume before and after treatment. Fifty-nine patients were treated with a single dose of 131I, 12 with two doses, and one with four doses. In 45 patients treated with one dose who remained euthyroid the median thyroid volume was reduced from 73 (interquartile range 50-106) ml to 29 (interquartile range 23-48) ml at 24 months. The median reduction was 40 (22-48) ml, half of which occurred within three months. Patients treated with two doses as well as those developing hypo- or hyper-thyroidism also had a significant reduction in thyroid volume. Eleven patients developed hypothyroidism (cumulative five year risk 22%). Side effects were few. In conclusion we find that 131I treatment of multinodular non-toxic goitre is an attractive alternative to surgery.     

Development of a luminescent bioassay for thyroid stimulating antibodies

The hyperthyroidism of Graves Disease (GD) is due to thyroid stimulating antibodies (TSAb) which are thyrotropin (TSH) agonists. They are detected routinely by measuring their ability to inhibit TSH binding to the receptor (TBII), which does not reflect their true biological activity. Current bioassays which measure cAMP by RIA, are not suitable for routine use. We have developed a luminescent bioassay for TSAb, by introducing a cAMP responsive luciferase construct into CHO cells stably expressing the human TSH receptor (TSHR). Clone lulul displays dose dependent TSH response detectable from 10 microU/ml and maximal at 10 mU/ml when a >25 fold increase in light output is obtained. 34 euthyroid sera were tested to determine a reference range, with values >1.5 relative light units (R.L.U.) being considered positive. An international TSAb standard responded in a dose dependent manner with 10 mIU/ml giving an R.L.U. of >10. The assay was adapted to a 96 well format for automatic readout and 100 treated GD samples (50 TBII negative and 50 TBII positive) were tested, 73% being positive. In contrast only 4% of 79 control sera from individuals with Hashimoto's, non-thyroid autoimmunity or multinodular goitre produced R.L.U. >1.5. When 44 of the GD sera were compared in a traditional salt-free bioassay, 61% were positive compared with 75% in the new luminescent assay. In conclusion, we have developed a luminescent bioassay for TSAb, using unfractionated serum which is capable of high throughput suitable for routine use.     

Fetal thyroid function

Cordocentesis has permitted the study of fetal thyroid function. In normal pregnancy, fetal blood thyroid-stimulating hormone (TSH), thyroid hormones and thyroid-binding globulin increase with advancing gestation demonstrating functional maturation of the pituitary, thyroid and liver, respectively. The administration of thyroid-releasing hormone to the mother produces a rapid increase in fetal TSH from at least 25 weeks gestation. In hypoxemic growth-retarded fetuses, the concentrations of TSH are higher, and the concentrations of total and free thyroxine are lower than in appropriately grown fetuses. In anemic fetuses from red cell-isoimmunized pregnancies, serum TSH and thyroid hormone concentrations are increased. In some chromosomally abnormal fetuses, particularly those with trisomy 21, TSH is increased.     

Outcomes measurement in today''s health care environment

The effects of smoking habits on thyroid function, echo-texture (nodules and/or cysts) and thyroid gland volume were determined by using ultrasound and measuring serum Thyroxin (T4), Triiodothyronine (T3), Thyrotropin (TSH) and TPO antibodies (ab-TPO) in 189 healthy smokers and non-smokers, randomly selected (111 females and 78 males) among the employees of our hospital and their relatives. When the entire group of subjects was considered the mean ratio of thyroid gland volume/body weight was found to be significantly higher in male (P < 0.05) and female (P < 0.05) smokers compared with non-smokers. In female smokers, mean serum thyroid-stimulating hormone (TSH) was lower (P < 0.05) and the degree of smoking was positively correlated with the ratio of thyroid gland volume/body weight (P < 0.05). However, when the subjects with a family history of goitre in first degree relatives were excluded from our study (14 females and 9 males), no significant differences in mean ratio of thyroid volume/weight or TSH between the remaining smokers and non-smokers were detected. In both sexes, the correlation between the degree of smoking and thyroid volume, although positive, did not reach statistical significance. No difference in prevalence of abnormal echogenicity and echo-texture (nodules and cysts) between smokers and non-smokers was detected. It is concluded that smoking habits present a goitrogenic effect only in subjects with a family history of goitre but have no influence on thyroid gland texture.     

Plasma renin and aldosterone in thyroid diseases

The effect of thyroid hormones on the renin-angiotensin-aldosterone system has not been fully resolved. Highly specific immunoassays for measurement of renin, aldosterone, free T4 (fT4), free T3 (fT3) and ultrasensitive TSH enables a direct and more accurate measurement of these hormones. We investigated the relationship between plasma renin, aldosterone and thyroid hormones in the basal state and after intravenous frusemide. This is a cross-sectional study involving 37 patients with thyrotoxicosis, 42 rendered euthyroid with normal fT4, fT3 and TSH levels, 17 with euthyroid levels of fT4 and fT3 but suppressed TSH, and 11 with hypothyroidism. Basal plasma renin was significantly higher in thyrotoxicosis (63.4 +/- 9.8 microU/ml, mean +/- SEM) compared to euthyroid (32.7 +/- 4.4 microU/ml) and hypothyroid (26.7 +/- 9.8 microU/ml). Basal plasma renin for euthyroid with suppressed TSH (41.0 +/- 7.4 microU/ml) was significantly higher than hypothyroid (p = 0.02). Basal plasma aldosterones were not significantly different except for suppressed TSH (157.7 +/- 13 pg/ml), which was higher than normal (109.9 +/- 10.4 pg/ml; p = 0.04). Following frusemide, plasma renin and aldosterone were significantly increased in all groups. Plasma renin was highly correlated to fT3 (r = 0.405, p < 0.001), total T3 (r = 0.359, p < 0.001), fT4 (r = 0.331, p < 0.001) and TSH (r = 0.300, p < 0.001) in the basal state, but less to total T4 (r = 0.248, p < 0.01). Plasma renin correlated poorly to serum aldosterone (r = 0.212, p < 0.03). This study clearly showed that regulation of renin was mainly influenced by fT3, and that aldosterone response to frusemide was blunted in thyrotoxicosis despite normal electrolytes.     

Adolescent abortion and parental notification: evidence for the importance of family functioning on the perceived quality of parental involvement in U.S. families

Hyperthyroidism is common and affects approximately 2% of women and 0.2% of men. The most common cause of hyperthyroidism is Graves' disease, an autoimmune disorder associated with circulating immunoglobulins that bind to and stimulate the thyrotropin (TSH) receptor, resulting in sustained thyroid overactivity. Toxic nodular goitres cause hyperthyroidism due to autonomous hyperfunctioning of localised areas of the thyroid. There are 3 recognised modalities of treatment for hyperthyroidism: antithyroid drugs, surgery and radioiodine. All are effective but no single method offers an absolute cure. Patients with Graves' disease may be prescribed antithyroid drugs over a period of 12 to 18 months with a view to inducing a long term remission. These drugs are also often given for a short period to render the patient euthyroid before definitive therapy with radioiodine or thyroidectomy. However, antithyroid drugs will not 'cure' hyperthyroidism associated with a toxic nodular goitre. The use of radioiodine as a first-line therapy for hyperthyroidism is growing. It is well tolerated, with the only long term sequelae being the risk of developing radioiodine-induced hypothyroidism. Radioiodine can be used in all age groups other than children, although it should also be avoided in pregnancy and during lactation. Pregnancy should be avoided for 4 months following its administration. Radioiodine may cause a deterioration in Graves' ophthalmopathy and corticosteroid cover may reduce the risk of this complication. The treatment of choice for toxic nodular goitre hyperthyroidism is radioiodine. Surgery, either subtotal or near-total thyroidectomy, has limited but specific roles to play in the treatment of hyperthyroidism: this approach is rarely used in patients with Graves' disease unless radioiodine has been refused or there is a large goitre causing symptoms of compression in the neck. The goal of surgery is to cure the underlying pathology while leaving residual thyroid tissue to maintain postoperative euthyroidism.     

Modern diagnostic methods for thyroid gland diseases]

The paper overviews the role of diagnostic procedures in evaluating patient with thyroid gland disease. It focuses on the diagnostics of functional disturbances and on the modern approach to the nodular goitre. The role of supersensitive, immunoenzymatic assay of TSH (sTSH) in the diagnostics of functional disturbances in underlined, particularly in subclinical course of thyroid gland diseases, or in diagnostically difficult cases. The complimentary role of tests' triangle-ultrasound, scintigraphy and fine needle biopsy in the evaluation of focal changes of the thyroid (nodular goitre) is discussed and the diagnostic algorithm of patient's qualification to surgery is proposed.