Iodine-induced hypothyroidism in full-term infants with congenital heart disease: more common than currently appreciated?

CONTEXT

Iodine is a micronutrient essential for thyroid hormone synthesis. Thyroid hormone is critical for normal neurocognitive development in young infants, and even transient hypothyroidism can cause adverse neurodevelopmental outcomes. Both iodine deficiency and excess can cause hypothyroidism. Although iodine-induced hypothyroidism is well recognized in premature infants, full-term neonates have received less attention. Infants with congenital heart disease (CHD) are commonly exposed to excess iodine from administration of iodinated contrast agents during cardiac catheterization as well as topical application of iodine-containing antiseptics and dressings; hence, this is a vulnerable population.

OBJECTIVE

We report three cases of iodine-induced hypothyroidism in full-term neonates with CHD after cardiac angiography and topical application of iodine-containing antiseptics and dressings in the operative setting.

RESULTS

Three neonates with CHD and normal thyroid function at birth developed hypothyroidism after exposure to excess iodine. Two of these infants had transient hypothyroidism, and one had severe hypothyroidism requiring ongoing thyroid replacement therapy. All infants were asymptomatic, with hypothyroidism detected incidentally in the inpatient setting due to repeat newborn screening mandated by the long duration of hospitalization in these infants.

CONCLUSIONS

Iodine-induced hypothyroidism may be under-recognized in infants with CHD exposed to excess iodine. Systematic monitoring of thyroid function should be considered to avoid potential long-term adverse neurodevelopmental effects of even transient thyroid dysfunction in this susceptible population.

Deiodination of thyroid hormones. A 30 year perspective (Berthold Memorial Award Lecture 1994)

It is truly a great honor to be the 1994 recipient of the Berthold Memorial Award from the German Endocrine Society which met in Würzburg, March 2-5. I am especially indebted to Drs. Köhrle and Wuttke for their kindness in making our visit to Würzburg so enjoyable and educational. Professor Berthold was the first to demonstrate the effects of a hormone on phenotypic expression when he transplanted testes to a castrated rooster, restoring its masculine appearance and behavior (Figure 1) (Berthold, 1849). Since 1960, when I joined the laboratory of the late Dr. Sidney H. Ingbar at the Thorndike Memorial Laboratory at the Boston City Hospital and Harvard Medical School, one of our major interest has been the peripheral metabolism of the thyroid hormones (Figure 2), especially the deiodination pathway (Figure 3). This review will be primarily based on our studies, although many other laboratories have made extremely important observations on thyroid hormone metabolism at the clinical, physiological, and molecular biological levels. I am indebted to many collaborators who have played major roles in many of the studies to be cited in this review. The principle colleagues are listed in Table 1. Since much of our work has been carried out simultaneously in rats, humans, and cell cultures, studies will be described under these three broad categories.

Transient congenital hypothyroidism in an iodine-replete area is not related to parental consanguinity, mode of delivery, goitrogens, iodine exposure, or thyrotropin receptor autoantibodies

OBJECTIVE

To assess transient congenital hypothyroidism (TCH) etiologies in two Iranian cities.

MATERIALS AND METHODS

Cord dried blood spot samples were collected from neonates in Tehran and Damavand. Serum TSH and T4 were measured in those with cord TSH > or =20 mIU/l. Normal serum values at 2-3 weeks of age confirmed transient hyperthyrotropinemia (THT), while persistently abnormal levels revealed congenital hypothyroidism (CH). Normal serum TSH and T4 4-6 weeks after levothyroxine replacement therapy discontinuation at 2-3 yr of age differentiated TCH from persistent CH.

RESULTS

Among 50,409 screened newborns, 9 (1:5601 births) were diagnosed as TCH and compared to 88 full-term neonates (>/=37 weeks' gestation) with THT and 45 normal (cord TSH<20 mIU/l) neonates. At a median age of 11 days, median (range) serum TSH values in TCH, THT, and normal neonates were 36.8 (13-130), 3.6 (0.1-13.3), and 2.9 (0.7-8.0) mIU/l (p<0.0001) and serum T4 values were 97 (36-168), 142 (74-232), and 160 (79-228 nmol/l), respectively (p=0.002). Urinary iodine concentration (UIC) >220 microg/l was observed in 5 (55.6%) of TCH neonates. The occurrence of TCH was not associated with gender, parental consanguinity, mode of delivery, pre- or post-natal consumption of goitrogens and/or thyroid affecting medications, TSH receptor autoantibodies, or neonatal UIC.

CONCLUSIONS

Elevated UIC was the most frequent finding in newborns with TCH but the distribution of excessive UIC was not significantly different among TCH, THT, and normal neonates. Since no other etiologies were found in TCH neonates without elevated UIC values, evaluation of other environmental and/or genetic factors is warranted.

National Health and Nutrition Examination Survey III thyroid-stimulating hormone (TSH)-thyroperoxidase antibody relationships demonstrate that TSH upper reference limits may be skewed by occult thyroid dysfunction

CONTEXT

The setting of the TSH upper reference limit impacts the diagnosis of mild hypothyroidism and is currently controversial.

OBJECTIVE

Our objective was to evaluate factors influencing the TSH reference range.

DESIGN

Nonpregnant subjects aged 12 yr and older from National Health and Nutrition Examination Survey III were used to study the relationships between TSH, thyroid peroxidase antibodies (TPOAb), and thyroglobulin antibodies in different ethnic groups.

RESULTS

TPOAb prevalence was lowest (<3%) when TSH was between 0.1 and 1.5 mIU/liter in women and between 0.1 and 2.0 mIU/liter in men and progressively increased to above 50% when TSH exceeded 20 mIU/liter. TSH reference range parameters (2.5th, 50th, and 97.5th percentiles) were analyzed according to thyroid antibody status, race/ethnicity, and age for the 14,202 subjects made up of non-Hispanic Blacks (B), non-Hispanic whites (W), and Mexican-Americans (M) who did not report thyroid disease or taking thyroid-altering medications and whose total T(4) was within the reference range. For each age group of each ethnicity, the inclusion of antibody-positive subjects increased TSH medians and upper limits (97.5th percentiles). The TSH upper limit was lower for the entire B cohort vs. W or M. However, this difference was lost when age cohorts with a similar prevalence of TPOAb (B age 40-49 yr vs. W and M age 20-29 yr) were compared.

CONCLUSIONS

Ethnic differences in TSH were not present when populations with the same relative frequency of thyroid antibodies were compared. TSH upper reference limits may be skewed by TPOAb-negative individuals with occult autoimmune thyroid dysfunction.

Clinical features of thyroid autoimmunity are associated with thyroiditis on histology and are not predictive of malignancy in 570 patients with indeterminate nodules on cytology who had a thyroidectomy

BACKGROUND

The relationship between thyroid autoimmunity and cancer is still uncertain.

PATIENTS

We approached this issue in 570 consecutive patients submitted to thyroidectomy for an indeterminate nodule on cytology. Thyroid autoimmunity was defined as positivity of circulating thyroid autoantibodies (TAb), autoimmune hypo- or hyperthyroidism, thyroid hypoechogenicity on ultrasound, and lymphocytic infiltration on histology.

RESULTS

TAb were found in 122/570 (21.4%), hypoechogenicity in 115/570 (20.1%), and lymphocytic infiltration in 117/570 (20.5%) of patients. The three features of thyroid autoimmunity were highly concordant: hypoechogenicity was observed in 71/448 (15.8%) patients with negative TAb and in 44/122 (36%) with positive TAb (P < 0.0001); lymphocytic infiltration was found in 53/448 (11.8%) patients with negative TAb and in 64/122 (52.4%) with positive TAb (P < 0.0001); hypoechogenicity on ultrasound was observed in 73/453 (16.1%) patients without, and in 42/117 (35.9%) with lymphocytic infiltration (P < 0.0001). None of these parameters was associated with malignancy. TAb were found in 32/135 (23.7%) patients with carcinoma and in 90/435 (20.6%) with a benign lesion (P = NS); hypoechogenicity was observed in 26/135 (19.2%) patients with carcinoma and in 89/435 (20.4%) patients with benign lesions (P = NS); lymphocytic infiltration was present in 28/135 (20.7%) patients with carcinoma and in 89/435 (20.4%) with benign lesions (P = NS). The frequency of cancer in 11 patients with clinically overt thyroid autoimmune disease did not differ from that observed in the whole study group.

CONCLUSION

In this group of patients with indeterminate thyroid nodules at cytology, clinical and pathological criteria of thyroid autoimmunity were strongly concordant and not associated with malignancy.

Serum thyrotropin receptor antibodies concentrations in patients with Graves' disease before, at the end of methimazole treatment, and after drug withdrawal: evidence that the activity of thyrotropin receptor antibody and/or thyroid response modify during the observation period

AIM AND METHODS

We performed a quantitative retrospective analysis of serum thyrotropin receptor antibody (TRAb) concentrations measured by a second-generation radioreceptor assay in 58 patients with Graves' disease (GD) at the onset of the disease, at the end of 18 month methimazole (MMI) treatment, and after MMI withdrawal in order to evaluate the correlation between the presence of these antibodies and the relapse of hyperthyroidism. Sixty healthy subjects were enrolled as a control group.

RESULTS

Before MMI treatment the best cutoff TRAb value for identifying patients with GD was 1.45 UI/L (specificity, 100%; sensitivity, 98.3%). At the end of MMI treatment, serum TRAb concentrations were significantly lower (p < 0.001) than those measured at baseline, but they were still significantly higher (p < 0.001) than those found in the control subjects. At the end of MMI treatment, 44 patients (75.9%) had positive TRAb values (>1.45 UI/L). After MMI withdrawal (median, 15 months), 34 patients (58.6%) became hyperthyroid, 4 patients (6.9%) became hypothyroid, and 20 patients (34.5%) remained euthyroid. There was a significant correlation between serum TRAb concentrations at the end of MMI treatment and the percentage of patients who became hyperthyroid (r: 0.56; p < 0.001) and the time of appearance of hyperthyroidism (r: -0.38; p = 0.03). All 4 patients with TRAb values below 0.9 UI/L at the end of MMI treatment remained euthyroid throughout the follow-up period. Among the 27 patients who had serum TRAb values higher than 4.4 UI/L, 23 developed hyperthyroidism and 4 hypothyroidism. The TRAb values between 0.9 and 4.4 UI/L did not discriminate between the 27 patients (46.6%) who remained euthyroid from those who had relapse of hyperthyroidism. Thus a different TRAb end of treatment cutoff was calculated to identify patients who became again hyperthyroid. This TRAb cutoff value was 3.85 UI/L (sensitivity, 85.3%; specificity, 96.5%). All but 1 patient who had serum TRAb values above 3.85 UI/L became hyperthyroid after MMI was withdrawn (positive predictive value, 96.7%). In these patients, relapse of hyperthyroidism was independent of the changes in serum TRAb concentrations (r: 0.27; p = 0.15) and occurred after a median period of 8 weeks (range, 4-48). Hyperthyroidism also developed in 5 of 24 patients who had serum TRAb concentrations lower than 3.85 UI/L at the end of MMI treatment. In these 5 patients the relapse of hyperthyroidism occurred after a median period of 56 weeks (range, 24-120) and was always accompanied by an increase in serum TRAb concentrations.

CONCLUSIONS

TRAb persist in the blood of most patients with GD after 18 months of MMI treatment. Both the frequency and the time of appearance of hyperthyroidism are closely correlated with serum TRAb concentrations at the end of MMI treatment. Our data would suggest that TRAb maintain stimulating activity after a full course of MMI treatment in the large majority of patients with GD. However, it is likely that the potency of these antibodies and/or the thyroid response to them change during treatment, as suggested by the different values measured in euthyroid control subjects and in euthyroid patients after MMI treatment.

Prevalence of goiter among schoolchildren from Gorgan, Iran, a decade after national iodine supplementation: association with age, gender, and thyroperoxidase antibodies

BACKGROUND

One decade after universal salt iodization in Iran, goiter prevalence, urinary iodine concentration (UIC) and thyroperoxidase antibody (TPOAb) values were assessed among schoolchildren in Gorgan, Iran.

METHODS

From 2003-2004, 500 girls and 900 boys aged 7-11 yr were evaluated for goiter by palpation. UIC was measured in 183 randomly-selected goitrous children. Serum TSH, T4, and TPOAb were measured in 53 goitrous and 30 non-goitrous children with adequate UIC.

RESULTS

Goiter was detected in 370 (26.4%) children. Goiter was present in 31% of girls and 17% of boys age 9 (p<0.012); 37% of girls and 20% of boys age 10 (p<0.003); and 52% of girls and 19% of boys age 11 (p<0.0001). Median (range) UIC for all goitrous children sampled was 190 (20-600) microg/l; 220 (30590) in boys and 170 (20-600) in girls (p=0.001). Eight point seven percent of goitrous children and 22% of goitrous girls aged 10-11 had UIC<100 microg/l, while 47% of the goitrous children had UIC> or =200 microg/ l. TPOAb was present in 52.8% of goitrous children and 10% of non-goitrous children (p=0.0001). TPOAb was present in 53.9% of 10-11 and 22.7% of 7-9 yr old goitrous and non-goitrous children (p=0.003) with adequate UIC. Median (range) TSH was 2.9 (0.3-10.9) mlU/I in TPO-positive and 1.8 (0.5-4.1) in TPO-negative children (p=0.001).

CONCLUSIONS

Gorgan, Iran, is an iodine-sufficient area and almost half of schoolchildren have more than adequate UIC. TPOAb is associated with endemic goiter. Despite sufficient UIC overall, some school-aged girls remain at risk of iodine deficiency.

Thyroid color flow doppler sonography and radioiodine uptake in 55 consecutive patients with amiodarone-induced thyrotoxicosis

Amiodarone-induced thyrotoxicosis (AMT) is a life-threatening condition, the appropriate management of which is achieved by identifying its different subtypes. Type 1 AIT develops in patients with underlying thyroid abnormalities and is believed to be due to increased thyroid hormone synthesis and release; Type 2 AIT occurs in patients with a normal thyroid gland and is an amiodarone-induced destructive process of the thyroid. Management differs in the two forms of AIT, since Type 1 usually responds to combined thionamides and potassium perchlorate therapy, while Type 2 is generally responsive to glucocorticoids. Mixed forms, characterized by coexistence of excess thyroid hormone synthesis and destructive phenomena, may require a combination of the two therapeutic regimens. In this cross-sectional prospective study, 55 consecutive untreated patients, whose AIT was subtyped according to clinical and biochemical criteria, were evaluated to assess the specificity of color flow doppler sonography (CFDS) and thyroidal radioiodine uptake (RAIU) in the differential diagnosis of AIT. Sixteen patients (6 men, 10 women, age 66+/-13 yr), who had diffuse or nodular goiter with or without circulating thyroid autoantibodies, were classified as Type 1 AIT; 39 patients (27 men, 12 women, age 65+/-13 yr) with apparently normal thyroids were classified as Type 2 AIT. All Type 1 patients had normal or increased thyroidal vascularity on CFDS, while Type 2 AIT patients had absent vascularity (p<0.0001). Thirteen Type 1 AIT patients had inappropriately normal or elevated thyroidal 3-h and 24-h RAIU values (range 6-37% and 10-58%, respectively), in spite of elevated values of urinary iodine excretion; the remaining 3 patients (two with nodular goiter, one with a thyroid adenoma) had low 3-h and 24-h RAIU values (range 1.1-3.0% and 0.9-4.0%, respectively). The latter patients, who were unresponsive to the combination of methimazole and potassium perchlorate, became euthyroid after the addition of glucocorticoids. Thirty-eight Type 2 AIT patients had low 3-h and 24-h RAIU values (range 0.4-3.7% and 0.2-3.0%, respectively), but one had inappropriately normal 3-h and 24-h RAIU values (6% and 13%, respectively). In conclusion, CFDS can accurately distinguish between Type 1 and Type 2 AIT, and in general the CFDS pattern is concordant with the thyroid RAIU. However, in 4 out of 55 patients (7%) the thyroid RAIU was discrepant, probably reflecting the coexistence of Type 1 and Type 2 AIT. Thus, assessment of both CFDS and RAIU may provide a more accurate subtyping of AIT and help in selecting the appropriate therapy. Finally, in long standing iodine sufficient areas, such as the United States, where the thyroid RAIU is consistently low irrespective of the etiology of the AIT, CFDS offers a rapid and available method to differentiate between Type 1 and Type 2 AIT.

A consensus report of the role of serum thyroglobulin as a monitoring method for low-risk patients with papillary thyroid carcinoma

Recent studies have provided new information regarding the optimal surveillance protocols for low-risk patients with differentiated thyroid cancer (DTC). This article summarizes the main issues brought out in a consensus conference of thyroid cancer specialists who analyzed and discussed this new data. There is growing recognition of the value of serum thyroglobulin (Tg) as part of routine surveillance. An undetectable serum Tg measured during thyroid hormone suppression of TSH (THST) is often misleading. Eight studies show that 21% of 784 patients who had no clinical evidence of tumor with baseline serum Tg levels usually below 1 micro g/liter during THST had, in response to recombinant human TSH (rhTSH), a rise in serum Tg to more than 2 micro g/liter. When this happened, 36% of the patients were found to have metastases (36% at distant sites) that were identified in 91% by an rhTSH-stimulated Tg above 2 micro g/liter. Diagnostic whole body scanning, after either rhTSH or thyroid hormone withdrawal, identified only 19% of the cases of metastases. Ten studies comprising 1599 patients demonstrate that a TSH-stimulated Tg test using a Tg cutoff of 2 micro g/liter (either after thyroid hormone withdrawal or 72 h after rhTSH) is sufficiently sensitive to be used as the principal test in the follow-up management of low-risk patients with DTC and that the routine use of diagnostic whole body scanning in follow-up should be discouraged. On the basis of the foregoing, we propose a surveillance guideline using TSH-stimulated Tg levels for patients who have undergone total or near-total thyroidectomy and (131)I ablation for DTC and have no clinical evidence of residual tumor with a serum Tg below 1 micro g/liter during THST.

Iopanoic acid rapidly controls type I amiodarone-induced thyrotoxicosis prior to thyroidectomy

Amiodarone-induced thyrotoxicosis (AIT) may develop either in apparently normal thyroid glands (Type II AIT) or in the presence of sub-clinical thyroid abnormalities (either autonomous goiter or latent Graves' disease; Type I AIT). Mixed forms also occur. While Type I AIT is due to iodine-induced excess thyroid hormone synthesis, Type II AIT is a form of amiodarone (possibly iodine) -induced destructive thyroiditis. Type I AIT is usually treated by combined thionamide and potassium perchlorate therapy, but may be resistant to therapy. On the other hand, Type II AIT often responds favorably to glucocorticoids and may not require further therapy once euthyroidism has been restored. Not infrequently, however, AIT (especially Type I) is resistant to conventional treatment, and several weeks or months may elapse before euthyroidism is restored. Thyroidectomy has been carried out in Type I AIT patients, but thyroid surgery in thyrotoxic patients, especially those with underlying cardiac problems, carries a high surgical risk. In this study we describe 3 patients with Type I AIT, who were successfully treated with a short course of iopanoic acid (IOP), an oral cholecystographic agent, which is rich in iodine and is a potent inhibitor of 5'-deiodinase, resulting in a marked decrease in the peripheral tissue conversion of T4 to T3, in preparation for thyroid surgery. Euthyroidism was rapidly restored in 7-12 days, allowing a subsequent safe and uneventful thyroidectomy in all cases. These patients were then treated with L-T4 for their hypothyroidism and amiodarone was safely re-instituted. We suggest that IOP is the drug of choice in the rapid restoration of euthyroidism prior to definitive thyroidectomy in patients with drug resistant Type I AIT.

Serum thyroglobulin concentrations and (131)I whole-body scan results in patients with differentiated thyroid carcinoma after administration of recombinant human thyroid-stimulating hormone

The use of recombinant human thyroid-stimulating hormone (rhTSH) has recently become available as an alternative diagnostic tool to assess the persistence and recurrence of differentiated thyroid carcinoma (DTC) in patients on thyroid hormone-suppressive therapy (THST) after near-total or total thyroidectomy and ablative doses of (131)I. We report the results of rhTSH administration in patients who were monitored for DTC.

METHODS

Thirty-three adult DTC patients (13 men, 20 women; mean age +/- SE, 45.6 +/- 2.31 y; age range, 21-65 y) underwent diagnostic follow-up after rhTSH administration at a dose of 0.9 mg once a day for 2 d. Whole-body scanning and serum thyroglobulin (Tg) measurement were performed after rhTSH administration. Patients were divided into 2 groups depending on serum Tg concentrations on THST: 29 patients had Tg concentrations of <2 ng/mL (group A) and 4 patients had Tg values of >2 ng/mL (group B).

RESULTS

In group A, Tg values remained at <2 ng/mL in 25 patients and increased from 1.1 +/- 0.14 ng/mL to 22.0 +/- 5.75 ng/mL (mean +/- SE) in 4 patients after rhTSH administration. Whole-body scanning did not reveal any uptake of (131)I in the 25 patients without an increase in Tg, whereas (131)I uptake was evident in 2 of the 4 patients with a rise in Tg. In group B, Tg values increased in all 4 patients from 17.3 +/- 6.35 ng/mL to 55.3 +/- 12.75 ng/mL, and (131)I uptake was evident in 3 of the 4 patients. No major adverse effects were reported after rhTSH administration.

CONCLUSION

Our results show that the measurement of serum Tg concentrations after rhTSH has a higher diagnostic value than whole-body scanning in detecting the persistence of thyroid tissue. Therefore, rhTSH should be administered in TSH-suppressed patients with basal serum Tg concentrations of <2 ng/mL because the increment in serum Tg concentrations may reveal the persistence of thyroid tissue in these patients.

Perchlorate clinical pharmacology and human health: a review

Potassium perchlorate has been used at various times during the last 50 years to treat hyperthyroidism. Since World War II ammonium perchlorate has been used as a propellant for rockets. In 1997, the assay sensitivity for perchlorate in water was improved from 0.4 mg/L (ppm) to 4 microg/L (ppb). As a result, public water supplies in Southern California were found to contain perchlorate ions in the range of 5 to 8 ppb, and those in Southern Nevada were found to contain 5 to 24 ppb. Research programs have been developed to assess the safety or risk from these exposures and to assist state and regulatory agencies in setting a reasonable safe level for perchlorate in drinking water. This report reviews the evidence on the human health effects of perchlorate exposure. Perchlorate is a competitive inhibitor of iodine uptake. All of its pharmacologic effects at current therapeutic levels or lower are associated with inhibition of the sodium-iodide symporter (NIS) on the thyroid follicular cell membrane. A review of the medical and occupational studies has been undertaken to identify perchlorate exposure levels at which thyroid hormone levels may be reduced or thyrotropin levels increased. This exposure level may begin in the 35 to 100 mg/d range. Volunteer studies have been designed to determine the exposure levels at which perchlorate begins to affect iodine uptake in humans. Such effects may begin at levels of approximately 1 mg/d. Environmental studies have assessed the thyroidal health of newborns and adults at current environmental exposures to perchlorate and have concluded that the present levels appear to be safe. Whereas additional studies are underway both in laboratory animals and in the field, it appears that a safe level can be established for perchlorate in water and that regulatory agencies and others are now trying to determine that level.

The various effects of amiodarone on thyroid function

Amiodarone, a benzofuranic-derivative iodine-rich drug used mostly for tachyarrhythmias, often causes changes in the peripheral metabolism of thyroid hormones mainly due to the inhibition of 5'-deiodinase activity: an increase in serum thyroxine and reverse triiodothyronine, and a decrease in serum triiodothyronine concentrations. Overt thyroid dysfunction, either amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH), occurring in 14% to 18% of patients receiving long-term treatment, may develop both in apparently normal thyroid glands and in glands with preexisting abnormalities. AIH is mainly due to the failure to escape from the acute Wolff-Chaikoff effect, and, in patients with thyroid autoimmune phenomena, to concomitant Hashimoto's thyroiditis. AIT is due to excess iodine-induced thyroid hormone synthesis (type I AIT) or to amiodarone-related destructive thyroiditis (type II AIT), although mixed forms often occur. Treatment of AIH consists of levothyroxine replacement therapy while continuing amiodarone therapy; alternatively, amiodarone can be discontinued, if possible, and the natural course toward euthyroidism can be accelerated by a short trial of potassium perchlorate. In type I AIT, the simultaneous administration of thionamides and potassium perchlorate is the treatment of choice, while in type II AIT steroids are the most useful therapeutic option. Mixed forms are best treated with a combination of thionamides, potassium perchlorate, and glucocorticoids. The low thyroidal 131I uptake usually makes radioiodine therapy not feasible, while thyroidectomy is a valid alternative in cases resistant to medical therapy.

The effects of amiodarone on the thyroid

Amiodarone is a benzofuranic-derivative iodine-rich drug widely used for the treatment of tachyarrhythmias and, to a lesser extent, of ischemic heart disease. It often causes changes in thyroid function tests (typically an increase in serum T(4) and rT(3), and a decrease in serum T(3), concentrations), mainly related to the inhibition of 5'-deiodinase activity, resulting in a decrease in the generation of T(3) from T(4) and a decrease in the clearance of rT(3). In 14-18% of amiodarone-treated patients, there is overt thyroid dysfunction, either amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH). Both AIT and AIH may develop either in apparently normal thyroid glands or in glands with preexisting, clinically silent abnormalities. Preexisting Hashimoto's thyroiditis is a definite risk factor for the occurrence of AIH. The pathogenesis of iodine-induced AIH is related to a failure to escape from the acute Wolff-Chaikoff effect due to defects in thyroid hormonogenesis, and, in patients with positive thyroid autoantibody tests, to concomitant Hashimoto's thyroiditis. AIT is primarily related to excess iodine-induced thyroid hormone synthesis in an abnormal thyroid gland (type I AIT) or to amiodarone-related destructive thyroiditis (type II AIT), but mixed forms frequently exist. Treatment of AIH consists of L-T(4) replacement while continuing amiodarone therapy; alternatively, if feasible, amiodarone can be discontinued, especially in the absence of thyroid abnormalities, and the natural course toward euthyroidism can be accelerated by a short course of potassium perchlorate treatment. In type I AIT the main medical treatment consists of the simultaneous administration of thionamides and potassium perchlorate, while in type II AIT, glucocorticoids are the most useful therapeutic option. Mixed forms are best treated with a combination of thionamides, potassium perchlorate, and glucocorticoids. Radioiodine therapy is usually not feasible due to the low thyroidal radioiodine uptake, while thyroidectomy can be performed in cases resistant to medical therapy, with a slightly increased surgical risk.

Effect of various doses of recombinant human thyrotropin on the thyroid radioactive iodine uptake and serum levels of thyroid hormones and thyroglobulin in normal subjects

Recombinant human TSH (rhTSH), usually given as 0.9-mg doses im on 2 successive days, increases serum thyroglobulin (Tg) and radioactive iodine uptake (RAIU) in residual thyroid tissue in patients with thyroid cancer. We previously reported that a single, relatively low dose of rhTSH (0.1 mg im) is a potent stimulator of T(4), T(3), and Tg secretion in normal subjects. The present study describes the effects of higher doses of rhTSH on thyroid hormone and Tg secretion. Six normal subjects for each dose group, having no evidence of thyroid disease, received either 0.3 or 0.9 mg rhTSH by im injection. Serum TSH, T(4), T(3), and Tg concentrations were measured at 2, 4, and 8 h and 1, 2, 3, 4, and 7 days after rhTSH administration. The peak serum TSH concentrations were 82 +/- 18 and 277 +/- 89 mU/L, respectively, for the 0.3- and 0.9-mg doses of rhTSH. Serum T(4), T(3), and Tg concentrations increased significantly in subjects receiving 0.3 and 0.9 mg rhTSH, with significant increases in T(4) and T(3) being observed before significant increases in serum TG: Peak concentrations of serum T(4), T(3), and Tg, after 0.3 mg rhTSH administration, were 100 +/- 19, 131 +/- 14, and 1035 +/- 724% above individual baselines, respectively. Similarly, peak concentrations of serum T(4), T(3), and Tg, after 0.9 mg rhTSH administration, were 102 +/- 16, 134 +/- 7, and 1890 +/- 768% above individual baselines, respectively. These data, compared with previously reported data for the responses to 0.1 mg rhTSH, indicated that 0.1, 0.3, and 0.9 mg rhTSH had similar quantitative stimulatory effects on thyroid hormone and Tg secretion, except that the T(4) response was greater in groups receiving 0.3 and 0.9 mg rhTSH than in the group receiving 0.1 mg rhTSH. We also studied the effect of rhTSH on the thyroid RAIU in the group that received 0.9 mg rhTSH. The 6- and 24-h RAIU values were significantly higher after rhTSH (pre-rhTSH, 6-h value = 12.5 +/- 1.8%; 24 h value = 23 +/- 2.7%; post-rhTSH, 6 h value = 27 +/- 4.8%; 24-h value = 41 +/- 4.2%). The stimulating effects of 0.9 mg rhTSH on the 6- and 24-h RAIUs were similar. rhTSH is a potent stimulator of T(4), T(3), and Tg secretion and the RAIU in normal subjects. Single doses greater than 0.1--0.3 mg do not seem to further enhance thyroid hormone or Tg secretion.

Effects of amiodarone administration during pregnancy on neonatal thyroid function and subsequent neurodevelopment

Amiodarone, a benzofuranic derivative, iodine-rich drug, has been used in pregnancy for either maternal or fetal tachyarrhythmias. Amiodarone, its main metabolite (desethylamiodarone) and iodine are transferred, albeit incompletely, through the placenta, resulting in a relevant fetal exposure to the drug and iodine overload. Since the fetus acquires the capacity to escape from the acute Wolff-Chaikoff effect only late in gestation, the iodine overload may cause fetal/neonatal hypothyroidism and goiter. Among the reported 64 pregnancies in which amiodarone was given to the mother, 11 cases (17%) of hypothyroidism in the progeny (10 detected at birth, 1 in utero) were reported, 9 non-goitrous (82%) and 2 (18%) associated with goiter. Hypothyroidism was transient in all cases, and only 5 infants were treated short-term with thyroid hormones. Only 2 newborns had transient hyperthyroxinemia, associated with low serum TSH concentrations in one. Neurodevelopment assessment of the hypothyroid infants, when carried out, showed in some instances mild abnormalities, most often reminiscent of the Non-verbal Learning Disability Syndrome; however, these features were also reported in some amiodarone-exposed euthyroid infants, suggesting that there might be a direct neurotoxic effect of amiodarone during fetal life. Breast-feeding was associated with a substantial ingestion of amiodarone by the infant, but in the few cases followed it did not cause changes in the newborn's thyroid function. In conclusion, amiodarone therapy during pregnancy may cause fetal/neonatal hypothyroidism and, less frequently, goiter. Thus, the use of amiodarone in pregnancy should be limited to maternal/fetal tachyarrhythmias which are resistant to other drugs or life-threatening. If amiodarone is used during gestation, a careful fetal/neonatal evaluation of thyroid function and morphology is warranted. It seems prudent to advise that fetal/neonatal hypothyroidism be treated, as soon as the diagnosis is made, even in utero, to avoid neurodevelopment abnormalities, although the latter may occur independently of hypothyroidism. If breast-feeding is allowed, careful evaluation of the infant's thyroid function and morphology is required because of the continuing exposure of the infant to the drug.

Regulation of the sodium iodide symporter by iodide in FRTL-5 cells

OBJECTIVE

The acute decrease in iodide organification in the thyroid in response to excess iodide is termed the acute Wolff-Chaikoff effect and normal organification resumes in spite of continued high plasma iodide concentrations (escape from the acute Wolff-Chaikoff effect). We have recently reported that large doses of iodide given to rats chronically decrease the sodium/iodide symporter (NIS) mRNA and protein, suggesting that escape is due to a decrease in NIS and subsequent iodide transport. We have now studied the effect of excess iodide on NIS in FRTL-5 cells to further explore the mechanisms whereby excess iodide decreases NIS.

DESIGN

FRTL-5 cells were employed and were incubated in the presence or absence of various concentrations of iodide. NIS mRNA and protein and the turnover of NIS were assessed.

METHODS

NIS mRNA was measured by Northern analysis, NIS protein by Western analysis and NIS turnover by pulse-chase labeling experiments.

RESULTS

Iodide (10(-) mol/l) had no effect on NIS mRNA in FRTL-5 cells at 24 and 48 h compared with cells cultured in the absence of iodide. However, excess iodide decreased NIS protein by 50% of control values at 24 h and by 70% at 48 h. This effect of iodide was dose dependent. Pulse-chase experiments demonstrated that there was no effect of iodide on new NIS protein synthesis and that the turnover of NIS protein in the presence of iodide was 27% faster than in the absence of added iodide.

CONCLUSIONS

Excess iodide does not decrease NIS mRNA in FRTL-5 cells but does decrease NIS protein, suggesting that in this in vitro thyroid cell model iodide modulates NIS, at least in part, at a post-transcriptional level. This iodide-induced decrease in NIS protein appears to be due, at least partially, to an increase in NIS protein turnover.

The effect of recombinant human tsh on the thyroid (123)i uptake in iodide treated normal subjects

Radioactive iodine therapy is often successful in the treatment of toxic or non-toxic multinodular goiter. However, when the patient has been exposed to iodine in the form of medication or radiocontrast agents prior to therapy, the thyroid radioactive iodine is often too low for successful ablation. Recently, administration of 0.9 mg of recombinant human TSH (rhTSH) has been shown to nearly double the 24-hour thyroid radioactive iodine uptake (RAIU) in euthyroid men living in the United States. In addition, 0.01 to 0.03 mg rhTSH administered 24 hours prior to (131)I in patients with a history of non-toxic multinodular goiter residing in an area of modestly low iodine intake, has also been shown to increase the 24-hour thyroid radioactive iodine uptake. We now have determined whether rhTSH administration prior to (123)I would increase the low thyroid RAIU in subjects treated with sodium iodide. Nine euthyroid men were given 15 mg iodide daily for 7 days. There was a marked increase in serum TSH values 8 and 24 hours after rhTSH administration, which induced elevated serum T4 and T3 concentrations. A 16 hour thyroid RAIU was measured at baseline, after 5 days of iodide administration, and either 8 or 32 hours after intramuscular administration of rhTSH. Administration of rhTSH 8 hours before (123)I to 4 subjects increased the 16 hour thyroid RAIU by 62% above the low post iodide thyroid RAIU. Administration of rhTSH 32 hours before (123)I administration to 5 subjects increased the 16 hour thyroid RAIU by 97% above the low iodide induced RAIU. Thus, the overall increase in the thyroid RAIU was 88% in the 9 subjects.

CONCLUSION

Recombinant TSH moderately increased the thyroid RAIU in subjects with depressed thyroid RAIU's during iodide administration and thus may be useful in preparing patients with non-toxic or toxic goiters and low thyroid RAIU's due to excess iodine for radioactive iodine treatment. Further studies to determine the optimal protocol to enhance the effect of rhTSH will be carried out.

The effect of droloxifene and estrogen on thyroid function in postmenopausal women

Estrogen is known to increase serum T4-binding globulin (TBG) concentrations, thereby increasing serum total T4 concentrations. Serum free T4 concentrations, however, remain normal. Tamoxifen, a selective estrogen receptor modifier (SERM), also raises serum TBG concentrations, but whether newer SERMs with less stimulatory action on the endometrium do so is not known. We, therefore, compared the effect of droloxifene, a SERM, and conjugated equine estrogen on pituitary-thyroid function in normal postmenopausal women. Ten women were treated for 6 weeks with conjugated estrogen (Premarin), 0.625 mg/day, and droloxifene, 60 mg/day, in a double-blind crossover study with an intervening 4-week no-treatment period. We measured serum T4, T3, TBG, free T4 index, and TSH at baseline and at the end of each 6-week period. The baseline values were compared with the 6-week values using paired t tests. The mean (+/- SD) serum TBG concentrations increased significantly during both treatment periods (baseline, 1.5+/-0.4 mg/dL; conjugated estrogens, 2.7+/-0.6 mg/dL; droloxifene, 2.1+/-0.6 mg/dL; P < 0.001 and P = 0.001, respectively). There were no significant changes in the serum free T4 index. Serum T4 and T3 concentrations increased during both treatment periods, however, the increase was significant only for T4 during the conjugated estrogen treatment period. The serum TSH concentrations increased significantly during both treatment periods (18% during conjugated estrogen and 11% during droloxifene), and the values remained within the normal range in all women. Administration of both conjugated estrogen and droloxifene for 6 weeks increases serum TSH and TBG concentrations, but does not alter free T4 index values in postmenopausal women.

Thyroid function changes related to use of iodinated water in the U.S. Space Program

BACKGROUND

The National Aeronautics and Space Administration (NASA) has used iodination as a method of microbial disinfection of potable water systems in U.S. spacecraft and long-duration habitability modules. A review of thyroid function tests of NASA astronauts who had consumed iodinated water during spaceflight was conducted.

METHODS

Thyroid function tests of all past and present astronauts were reviewed. Medical records of astronauts with a diagnosis of thyroid disease were reviewed. Iodine consumption by space crews from water and food was determined. Serum thyroid-stimulating hormone (TSH) and urinary iodine excretion from space crews were measured following modification of the Space Shuttle potable water system to remove most of the iodine.

RESULTS

Mean TSH significantly increased in 134 astronauts who had consumed iodinated water during spaceflight. Serum TSH, and urine iodine levels of Space Shuttle crewmembers who flew following modification of the potable water supply system to remove iodine did not show a statistically significant change. There was no evidence supporting association between clinical thyroid disease and the number of spaceflights, amount of iodine consumed, or duration of iodine exposure.

CONCLUSIONS

It is suggested that pharmacological doses of iodine consumed by astronauts transiently decrease thyroid function, as reflected by elevated serum TSH values. Although adverse effects of excess iodine consumption in susceptible individuals are well documented, exposure to high doses of iodine during spaceflight did not result in a statistically significant increase in long-term thyroid disease in the astronaut population.