Modifications of thyroid function induced by chronic administration of iodide in the presence of "autonomous" thyroid tissue

Is there still a role for thyroid scintigraphy in the workup of a thyroid nodule in the era of fine needle aspiration cytology and molecular testing?

Thyroid scintigraphy is now rarely used in the work-up of a thyroid nodule except in the presence of a low TSH value. Therefore, autonomously functioning thyroid nodules (AFTNs) with a normal TSH value are diagnosed only in the rare medical centers that continue to use thyroid scan systematically in the presence of a thyroid nodule. In this review, we discuss the prevalence of AFTN with a normal TSH level and the possible consequences of performing fine needle aspiration cytology (FNAC) in an undiagnosed AFTN. We also discuss the risk of malignant AFTN which may be higher than previously stated.

microRNA expression in autonomous thyroid adenomas: Correlation with mRNA regulation

The objective of the study was to identify the deregulated miRNA in autonomous adenoma and to correlate the data with mRNA regulation. Seven autonomous adenoma with adjacent healthy thyroid tissues were investigated. Twelve miRNAs were downregulated and one was upregulated in the tumors. Combining bioinformatic mRNA target prediction and microarray data on mRNA regulations allowed to identify mRNA targets of our deregulated miRNAs. A large enrichment in mRNA encoding proteins involved in extracellular matrix organization and different phosphodiesterases were identified among these putative targets. The direct interaction between miR-101-3p and miR-144-3p and PDE4D mRNA was experimentally validated. The global miRNA profiles were not greatly modified, confirming the definition of these tumors as minimal deviation tumors. These results support a role for miRNA in the regulation of extracellular matrix proteins and tissue remodeling occurring during tumor development, and in the important negative feedback of the cAMP pathway, which limits the consequences of its constitutive activation in these tumors.

Thyroid physiology

The thyroid gland produces thyroid hormone, which has clinically important actions practically in every system in the human body. Detailed knowledge of the physiology of the thyroid gland is critical for the proper management of thyroid disorders. The molecular biology of thyroid function is being studied in great detail. Clinically important molecules, such as the thyroid-stimulating hormone receptor and the sodium/iodide symporter, have been identified and well characterized. Such discoveries have significantly improved our understanding of thyroid physiology. As a result, new diagnostic and therapeutic approaches for the management of thyroid disorders are now available or in development.

Iodine excess

Several mechanisms are involved in the maintenance of normal thyroid hormone secretion, even when iodine intake exceeds physiologic needs by a factor of 100. The sodium-iodide symporter system contributes most to this stability. Faced with an iodine excess, it throttles the transport of iodide into the thyroid cells, the rate-limiting step of hormone synthesis. Even before the iodine symporter reacts, a sudden iodine overload paradoxically blocks the second step of hormone synthesis, the organification of iodide. This so-called Wolff-Chaikoff effect requires a high (>or=10(-3) molar) intracellular concentration of iodide. The block does not last long, because after a while the sodium-iodide symporter shuts down; this allows intracellular iodide to drop below 10(-3) molar and the near-normal secretion to resume. In some susceptible individuals (e.g., after radio-iodine treatment of Graves' disease or in autoimmune thyroiditis), the sodium-iodide symporter fails to shut down, the intracellular concentration of iodide remains high and chronic hypothyroidism ensues. To complicate matters, iodine excess may also cause hyperthyroidism. The current explanation is that this happens in persons with goitres, for example, after long-standing iodine deficiency. These goitres may contain nodules carrying a somatic mutation that confers a 'constitutive' activation of the TSH receptor. Being no more under pituitary control, these nodules overproduce thyroid hormone and cause iodine-induced hyperthyroidism, when they are presented with sufficient iodine. These autonomous nodules gradually disappear from the population after iodine deficiency has been properly corrected. More recent studies suggest that chronic high iodine intake furthers classical thyroid autoimmunity (hypothyroidism and thyroiditis) and that iodine-induced hyperthyroidism may also have an autoimmune pathogenesis.

Gene expression in thyroid autonomous adenomas provides insight into their physiopathology

The purpose of this study was to use the microarray technology to define expression profiles characteristic of thyroid autonomous adenomas and relate these findings to physiological mechanisms. Experiments were performed on a series of separated adenomas and their normal counterparts on Micromax cDNA microarrays covering 2400 genes (analysis I), and on a pool of adenomatous tissues and their corresponding normal counterparts using microarrays of 18,000 spots (analysis II). Results for genes present on the two arrays corroborated and several gene regulations previously determined by Northern blotting or microarrays in similar lesions were confirmed. Five overexpressed and 24 underexpressed genes were also confirmed by real-time RT-PCR in some of the samples used for microarray analysis, and in additional tumor specimens. Our results show: (1) a change in the cell populations of the tumor, with a marked decrease in lymphocytes and blood cells and an increase in endothelial cells. The latter increase would correspond to the establishment of a close relation between thyrocytes and endothelial cells and is related to increased N-cadherin expression. It explains the increased blood flow in the tumor; (2) a homogeneity of tumor samples correlating with their common physiopathological mechanism: the constitutive activation of the thyrotropin (TSH)/cAMP cascade; (3) a low proportion of regulated genes consistent with the concept of a minimal deviation tumor; (4) a higher expression of genes coding for specific functional proteins, consistent with the functional hyperactivity of the tumors; (5) an increase of phosphodiesterase gene expression which explains the relatively low cyclic AMP levels measured in these tumors; (6) an overexpression of antiapoptotic genes and underexpression of proapoptotic genes compatible with their low apoptosis rate; (7) an overexpression of N-cadherin and downregulation of caveolins, which casts doubt about the use of these expressions as markers for malignancy.

Hyperthyroidism: advantages and disadvantages of medical therapy

The most common causes of hyperthyroidism are Graves' disease, toxic nodular goiter, and iodine-induced hyperthyroidism. Hyperthyroidism can be treated medically with antithyroid drugs or radioactive iodine, or surgically. Multiple clinical factors must be weighed when choosing a treatment modality. All of the available forms of therapy have advantages and disadvantages, and treatment choices must be individualized.

Iodine excess and hyperthyroidism

150 microg iodine are daily required for thyroid hormone synthesis. The thyroid gland has intrinsic mechanisms that maintain normal thyroid function even in the presence of iodine excess. Large quantities of iodide are present in drugs, antiseptics, contrast media and food preservatives. Iodine induced hyperthyroidism is frequently observed in patients affected by euthyroid iodine deficient goiter when suddenly exposed to excess iodine. Possibly the presence of autonomous thyroid function permits the synthesis and release of excess quantities of thyroid hormones. The presence of thyroid autoimmunity in patients residing in iodine-insufficient areas who develop iodine-induced hyperthyroidism has not been unanimously observed. In iodine-sufficient areas, iodine-induced hyperthyroidism has been reported in euthyroid patients with previous thyroid diseases. Euthyroid patients previously treated with antithyroid drugs for Graves' disease are prone to develop iodine-induced hyperthyroidism. As well, excess iodine in hyperthyroid Graves' disease patients may reduce the effectiveness of the antithyroid drugs. Occasionally iodine-induced hyperthyroidism has been observed in euthyroid patients with a previous episode of post-partum thyroiditis, amiodarone destructive or type II thyrotoxicosis and recombinant interferon-alpha induced destructive thyrotoxicosis. Amiodarone administration may induce thyrotoxicosis. Two mechanisms are responsible for this condition. One is related to excess iodine released from the drug, approximately 9 mg of iodine following a daily dose of 300 mg amiodarone. This condition is an iodine-induced thyrotoxicosis or type I amiodarone-induced thyrotoxicosis. The other mechanism is due to the amiodarone molecule that induces a destruction of the thyroid follicles with a release of preformed hormones. This condition is called amiodarone-induced destructive thyrotoxicosis or type II thyrotoxicosis. Patients developing type I thyrotoxicosis in general have preexisting nodular goiter whereas those developing type II thyrotoxicosis have a normal thyroid gland. The latter group of patients, after recovering from the destructive process, may develop permanent hypothyroidism as the consequence of fibrosis of the gland.

Iodine absorption in patients undergoing ERCP compared with coronary angiography

BACKGROUND

Systemic absorption of iodinated contrast material occurs during endoscopic retrograde cholangiopancreatography (ERCP), the clinical significance of which has not yet been determined.

METHODS

Urinary iodine excretion was measured before and after coronary angiography (n = 20) and ERCP (n = 12). Thyroid hormone levels were determined before iodine load and after 6 and 24 weeks.

RESULTS

Before coronary angiography, iodine excretion was 101 +/- 38.3 micromol/mol creatinine and increased to 865. 10(5) +/- 721. 10(5) micromol/mol on the next day (p </= 0.001). After 6 weeks, it was still elevated (167 +/- 88.8 micromol/mol, p < 0.01). Before ERCP, iodine excretion was 115 +/- 60.3 micromol/mol and reached a peak of 5.3. 10(5) +/- 4.9. 10(5) micromol/mol (p < 0.001). Six weeks later, it had returned to baseline. Two patients in the coronary angiography group but none in the ERCP group had suppressed thyrotropin after 6 weeks.

CONCLUSIONS

The systemic iodine load during ERCP is approximately 0.6% of the iodine load during coronary angiography. Therefore routine measurement of thyroid hormones before ERCP is not recommended.

Autonomy in endemic goiter

The occurrence of hyperthyroidism in many individuals after introduction of iodine prophylaxis in endemic goiter areas can have dramatic consequences for the affected individuals. It indicates that in such individuals the increase of serum thyroid hormone level in response to iodine supplementation does not exert its normal negative feedback on thyroid activity, ie, that in such individuals some thyroid tissue has become autonomous. In this short review we summarize what is known about the possible mechanisms, cause, diagnosis, and consequences of thyroid autonomy.

Iodine-induced hyperthyroidism: occurrence and epidemiology

We have critically reviewed the available information on iodine-induced hyperthyroidism (IIH) from published sources and other reports as well as the experience of the authors in Tasmania, Zaire, Zimbabwe, and Brazil. Administration of iodine in almost any chemical form may induce an episode of thyrotoxicosis (IIH). This has been observed in epidemic incidence in several countries when iodine has been given as prophylaxis in a variety of vehicles, but the attack rate as recorded has been low. IIH is most commonly encountered in older persons with long standing nodular goiter and in regions of chronic iodine deficiency, but instances in the young have been recorded. It customarily occurs after an incremental rise in mean iodine intake in the course of programs for the prevention of iodine deficiency, or when iodine-containing drugs such as radiocontrast media or amiodarone are administered. The biological basis for IIH appears most often to be mutational events in thyroid cells that lead to autonomy of function. When the mass of cells with such an event becomes sufficient and iodine supply is increased, the subject may become thyrotoxic. These changes may occur in localized foci within the gland or in the process of nodule formation. IIH may also occur with an increase in iodine intake in those whose hyperthyroidism (Graves' disease) is not expressed because of iodine deficiency. The risks of IIH are principally to the elderly who may have heart disease, and to those who live in regions where there is limited access to medical care. More information is needed on the long-term health impact of IIH or "subclinical" IIH, especially in the course of prophylaxis programs with iodized salt or iodinated oil in regions where access to health care is limited.

The disorders induced by iodine deficiency

This paper reviews present knowledge on the etiology, pathophysiology, complications, prevention, and therapy of the disorders induced by iodine deficiency. The recommended dietary allowances of iodine are 100 micrograms/day for adults and adolescents, 60-100 micrograms/day for children aged 1 to 10 years, and 35-40 micrograms/day in infants aged less than 1 year. When the physiological requirements of iodine are not met in a given population, a series of functional and developmental abnormalities occur including thyroid function abnormalities and, when iodine deficiency is severe, endemic goiter and cretinism, endemic mental retardation, decreased fertility rate, increased perinatal death, and infant mortality. These complications, which constitute a hindrance to the development of the affected populations, are grouped under the general heading of iodine deficiency disorders (IDD). At least one billion people are at risk of IDD. Iodine deficiency, therefore, constitutes one of the most common preventable causes of mental deficiency in the world today. Most of the affected populations live in mountainous areas in preindustrialized countries, but 50 to 100 million people are still at risk in Europe. The most important target groups to the effects of iodine deficiency from a public health point of view are pregnant mothers, fetuses, neonates, and young infants because the main complication of IDD, i.e., brain damage resulting in irreversible mental retardation, is the consequence of thyroid failure occurring during pregnancy, fetal, and early postnatal life. The main cause of endemic goiter and cretinism is an insufficient dietary supply of iodine. The additional role of naturally occurring goitrogens has been documented in the case of certain foods (milk, cassava, millet, nuts) and bacterial and chemical water pollutants. The mechanism by which the thyroid gland adapts to an insufficient iodine supply is to increase the trapping of iodide as well as the subsequent steps of the intrathyroidal metabolism of iodine leading to preferential synthesis and secretion of triiodotyronine (T3). They are triggered and maintained by increased secretion of TSH, which is ultimately responsible for the development of goiter. The acceleration of the main steps of iodine kinetics and the degree of hyperstimulation by TSH are much more marked in the pediatric age groups, including neonates, than in adults, and the development of goiter appears as an unfavorable side effect in the process of adaptation to iodine deficiency during growth. The most serious complication of iodine deficiency is endemic cretinism, a syndrome characterized by irreversible mental retardation together with either a predominant neurological syndrome or predominant hypothyroidism, or a combination of both syndromes.(ABSTRACT TRUNCATED AT 400 WORDS)

Amiodarone-induced thyrotoxicosis: is there a place for surgery?

Amiodarone-induced hyperthyroidism has on most instances been reported as mild, and thyroid functions return to normal after discontinuation of the drug. Nevertheless, life-threatening amiodarone-induced thyrotoxicosis has also been described. Conventional treatments such as antithyroid drugs (thionamide) and corticosteroids are essentially ineffective or fail to alter the dramatic course of the thyroid crisis. This limited effectiveness of medical therapy, particularly in patients with previously neglected or unknown thyroid disease, prompted us to intervene surgically. We report a series of nine patients who underwent total or near-total thyroidectomy as a first-line therapy for five of them. Surgery resulted in rapid resolution of thyrotoxicosis with an uneventful postoperative course. This approach has the advantage of immediate effectivity, low risk of relapse, and appears to be the only treatment that permits continued therapy with amiodarone when the drug appears needed to control a life-threatening arrhythmia.

Iodine-induced hyperthyroidism due to nonionic contrast radiography in the elderly

PURPOSE

To identify the number of cases of hyperthyroidism that followed the performance of contrast radiography in elderly patients at a geriatric hospital in a non-iodine-deficient area and to determine the clinical course of the condition.

PATIENTS AND METHODS

All patients over a 20-month period with biochemical hyperthyroidism (plasma free thyroxine level greater than 25.0 pmol/L and thyroid-stimulating hormone level less than 0.10 IU/L) were identified. Clinical features of hyperthyroidism and exposure to nonionic contrast media radiographs within the previous 12 months were sought. Follow-up extended from 6 to 22 months.

RESULTS

A total of 28 patients with hyperthyroidism (aged 70 to 96 years) were identified. Seven patients (25%) had documented biochemical development of hyperthyroidism (five) or subsequent hyperthyroidism (two) 3 to 8 weeks after nonionic contrast media radiography. The four patients who underwent scanning had a multinodular thyroid, and thyroid antibodies were not detected in five of five patients. Although the condition appeared self-limited and six of six patients were euthyroid after 18 months, the condition was not benign; progress and recovery were adversely affected by hyperthyroidism. Four patients had a good response to treatment with an antithyroid drug (carbimazole).

CONCLUSION

Iodine-induced thyrotoxicosis following contrast radiography was found in 7 of 28 cases of hyperthyroidism seen at a geriatric hospital. Although the condition appears ultimately self-limited, pharmacologic control of severe clinical features may be required. The frequency of this condition in a non-iodine-deficient area appears related to the more common occurrence of autonomous thyroid nodules in the elderly. Because performance of contrast radiography is more common in this age group, the recognition and treatment of iodine-induced thyrotoxicosis are of increasing clinical importance.

Iodide-induced thyrotoxicosis in a thyroidectomized patient with metastatic thyroid carcinoma

An unusual case of iodide-induced thyrotoxicosis is documented in this article. The patient was a 64-year-old euthyroid man with acromegaly. He also had multiple follicular and papillary thyroid carcinomas with a metastatic lesion in the lumbar vertebrae. After a total thyroidectomy, he became slightly hypothyroid, and the lumbar lesion began to incorporate 131I by scintigraphy. When an iodine-containing contrast medium happened to be injected, a transient increase of serum thyroid hormone level was observed. After complete thyroid ablation with 83 mCi of 131I, the oral administration of 100 mg of potassium iodide for 7 days induced a prominent increase of serum thyroid hormone level. These findings indicated that the metastatic thyroid carcinoma could produce excess thyroid hormone insofar as a sufficient amount of iodide was given. Although this is the first report of such a case, iodide-induced thyrotoxicosis may not be rare in patients with thyroid carcinomas because the Wolff-Chaikoff effect is thought to be lost, and the organic iodinating activity and lysosomal protease activity are well-preserved.

Increased serum thyroglobulin concentrations and impaired thyrotropin response to thyrotropin-releasing hormone in euthyroid subjects with endemic goiter in Sicily: their relation to goiter size and nodularity

Serum thyroglobulin (Tg), T4, T3, FT4, FT3, TSH concentrations and TSH response to iv TRH (delta TSH) were measured in 56 consecutive patients with (multi) nodular goiter from a severely iodine-deficient endemic goiter area in Northeastern Sicily and in 11 non goitrous euthyroid individuals living in the same area. Serum Tg concentrations were sharply increased in goitrous subjects (453 +/- 476 ng/ml) and related to thyroid size and the presence of nodules (chi 2 = 43.5, p less than 0.0005). Serum TSH levels measured in goitrous patients (2.1 +/- 0.9 microU/ml) were significantly lower than those measured in nongoitrous iodine deficient subjects (3.1 +/- 0.9 microU/ml, p less than 0.001) and decreased with increasing goiter size and nodularity (chi 2 = 27.3, p less than 0.05). A similar pattern was shown by the analysis of the delta TSH (chi 2 = 43.1, p less than 0.0005). These results suggest that at least a part of the largest and multinodular goiters become autonomously functioning with duration and growing in size. In 13 goitrous patients with absent or impaired response to TRH, a significant direct relation was apparent between log-Tg and goiter size and nodularity (r = 0.64) with an inverse relationship between serum FT3 and delta TSH (r = 0.73). A computed program analysis based on the combination of different independent variables (x) including age, thyroid size and nodularity, serum TSH, log-Tg and FT3, indicated the existence of a significant negative relationship between these variables and the TSH response to TRH (r = 0.75, p = 0).(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperthyroidism due to Graves' disease and due to autonomous goiter

An attempt was made to classify 326 patients with hyperthyroidism due to Graves' disease and due to autonomous goiter in an area of endemic iodine deficient goiter using the following two sets of criteria: Primary criteria: the presence of endocrine ophthalmopathy (Graves' disease) and the absence of endocrine ophthalmopathy and the absence of microsomal antibodies greater than or equal to 1:1600 (autonomous goiter). Sixty-nine percent of the patients could be divided in the two groups with the aid of these criteria. Secondary criteria: age greater than 50 years, presence of a goiter, presence of thyroid nodules, activity distribution in the scan, iodine intake determined by iodine excretion in the urine. These criteria had to be applied in the 31% of the patients who could not be divided into one of the two groups using the primary criteria. The secondary criteria were accumulative. Using these criteria 55% of the 326 patients were classified as having Graves' disease and 45% as having autonomous goiter. The probability of correct grouping when both primary and secondary criteria were applied was estimated to be 90% compared to 54% when we used only the classical terms, i.e. endocrine ophthalmopathy and diffuse goiter on the one hand and multinodular goiter without endocrine ophthalmopathy on the other hand. In a second group of 120 hyperthyroid patients classified in this way, thyrotropin displacing activity was determined independently. Its prevalence was 79% in patients classified as having Graves' disease but only 3% in those classified as having autonomous goiter. The prevalence of TDA observed in patients who presumably had autonomous goiter was in the same range as in the following groups: 45 normal individuals; 126 patients with euthyroid goiter; and in 112 patients with euthyroid and hyperthyroid autonomous adenoma.(ABSTRACT TRUNCATED AT 250 WORDS)

[Operative indications and surgical procedure in iodine-induced hyperthyroidism]

Clinical course, indications for surgical treatment, and results of treatment in 8 female patients with iodine induced thyrotoxicosis (IIT) are reported. The diagnosis of IIT could be established in all patients by a) clinical hyperthyroidism, b) increased T3 and T4 serum concentrations, and c) previous iodine contamination. Sources of iodine were radiographic contrast agents for urography (n = 4), oral cholecystography (n = 3), intravenous cholangiography (n = 1), phlebography (n = 1), and cranial computer tomography (n = 1). The onset of hyperthyroidism occurred 1-8 weeks after iodine exposure. Indications for surgical treatment of IIT were: 1. autonomous nodular goiter (n = 6), and 2. iodine exacerbation of preexisting thyrotoxicosis in patients with Graves' disease (n = 2). Corresponding to the different pathogenesis of autonomous and immunogenetic goiter the following surgical treatment is recommended: Enucleation of solitary autonomous adenomas or unilateral lobectomy in case of large adenomas, subtotal bilateral lobectomy in toxic multinodular goiter or, preferentially, unilateral lobectomy combined with subtotal resection of the contralateral thyroid lobe; "Near-total" thyroidectomy in Graves' immunopathy.

Toxic nodular goitre

Toxic nodular goitre is the late result of a slow growth process generating new daughter follicles from the mother follicles of a normal thyroid gland. Since the normal follicular shell is not built up by monoclonal epithelial cells, but rather by cells with widely variable functional equipment, daughter follicles generated by the preferential replication of particular mother follicular cells endowed with a high growth potential, may be different from mother follicles. For instance, the progeny of follicles may have a higher or lower iodine metabolism than their progenitor follicles. Some of the newly generated follicles have a high autonomous, i.e. TSH-independent, iodine turnover, while some others have a high autonomous growth potential. The degree of autonomous function is entirely independent of that of growth. In the process of goitrogenesis, newly generated follicles may, in addition, acquire new forms of expressing genetic functions. Such new traits, e.g. a particular growth pattern, may become inheritable and are then passed on from mother to daughter cells. The result is the most characteristic of all hallmarks of nodular goitres, which is the heterogeneity of structure and function between two diseased glands and even between closely adjacent follicles of the same gland. Greatly uneven intrinsic replication rates between different follicular cells and equally varying independency on growth stimuli account for regional differences in goitre growth. This, together with a network of fibrous scars interfering with unimpeded expansion of the growing follicle population, invariably produces a nodular growth pattern of the goitre. TSH certainly does not account for the growth of this type of goitre. Instead, a number of thyroid growth factors, including growth-stimulating immunoglobulins akin to those found in Graves' disease, have been discovered in recent years. Once the number of follicular cells with high intrinsic growth potential has become large enough under the impact of extrathyroidal growth stimuli, goitre growth may become autonomous and self-perpetuating. Whether or not a nodular goitre will produce thyrotoxicosis is a function of the number of follicles with high intrinsic iodine turnover which happen to be generated in the course of goitrogenesis. In contrast to thyrotoxicosis in Graves' disease, hyperthyroidism in nodular goitre is a very slowly progressing, insidiously evolving complication.

[Diagnostic procedure in suspected functional disorders of the thyroid gland]

In an attempt to derive diagnostic concepts for thyroid diseases we present pathophysiological models for the prevalent thyroid disorders. 'Euthyroid goiter' is a disease mainly caused by iodine deficiency but an additional immunopathogenesis was recently proposed. The 'immunthyropathy' is the thyroid disease with orbitopathy and other extraglandular immunological manifestations. A complete model of the immunological phenomena which begin with a tolerance defect is given, and both the T-cell, and B-cell-mediated pathways are detailed. The complex interaction of immunoglobulins at the thyroid-stimulating hormone receptor and their dependency on human leukocyte antigen loci are presented. The peripheral metabolism depends ultimately upon a prevalence of thyroid gland stimulation (thyrotoxicosis) or glandular destruction (hypothyroidism) and this is true for overt thyroid disease under antithyroid drug therapy or any other therapy. Euthyroidism during 'immunethyropathy' is presented as an equilibrium between thyroid stimulation and destruction. This concept allows an exact description of the thyroid disease and the resulting clinical situation provided that established laboratory tests are used as suggested by the model. 'Disseminated thyroid autonomy and autononous thyroid adenoma' develops during goitrous thyroid disease as a consequence of uncoupling of thyroid cellular growth stimulation, iodine utilization, and thyroid hormone synthesis. The polyclonal origin seems more frequent than monoclonal foci. The size of autononous tissue and individual iodine supply determines the endocrine function in this disease. The TRH test monitors with great sensitivity subtle increases in T4 or T3 production and indicates critical clinical situations earlier than the scintiscan.(ABSTRACT TRUNCATED AT 250 WORDS)

Five patients with iodine-induced hyperthyroidism

Iodine-induced hyperthyroidism has been frequently described when iodine is introduced into an iodine-deficient area. However, it may also occur in patients with and without previous thyroid disease residing in iodine-sufficient areas. Five patients with iodine-induced hyperthyroidism seen in a 12-month period are described. All were exposed to iodine in the form of commonly used drugs (Betadine, Iodo-Niacin, amiodarone, and radiographic contrast dyes). The cause of iodine-induced hyperthyroidism is unclear, but it is probably more common in patients with goiters containing previously existing areas of autonomous function or iodine-poor thyroglobulin. Iodine-induced hyperthyroidism usually abates after iodine withdrawal in patients with multinodular goiters or normal thyroid glands. The hyperthyroidism is usually treated with beta-blockers and antithyroid thionamide drugs, although reinstitution of iodine to block thyroid hormone release or corticosteroids occasionally may be necessary. Iodine-containing drugs should be given with caution to patients with underlying thyroid disease.

Iodine contamination as a cause of hyperthyroidism or lack of TSH response to TRH stimulation (results based on a screening investigation)

The sera of all patients with completely suppressed TSH response to TRH obtained during one year (n = 668), and of those with diminished TSH response (n = 153) were screened for total serum iodine content. The ratio between serum iodine and thyroxine iodine below 1.5 indicates none or only a minor degree of iodine contamination, whereas a ratio above 1.5 is a clear index of exogenous iodine contamination. Eighty-four (21.3%) of 395 patients with overt hyperthyroidism were iodine contaminated. No prevalence of hyperthyroidism with hyperthyroxinemia could be detected as compared to T3-hyperthyroidism in the contaminated groups. Surprisingly, the iodine contamination rate was twice as high in 273 patients with suppressed TSH response to TRH but normal thyroid hormone levels and not fully explained thyroidal diseases. A high incidence of multifocal autonomous adenomas of the thyroid is the most probable explanation for the TSH suppression in iodine contaminated patients with normal thyroid hormone levels.

Alterations in thyroid function after cholecystographic contrast agents

The radiographic contrast agents commonly used for oral cholecystography have diverse effects on thyroid hormones in man. They may: (i) decrease serum triiodothyronine (T3) and increase reverse T3 in both hyperthyroid and euthyroid subjects, an effect attributable to inhibition of phenolic (outer) ring deiodination of iodothyronines; (ii) acutely increase serum thyroxine (T4) by displacing it from the liver, so inviting an erroneous diagnosis of hyperthyroidism; (iii) precipitate hyperthyroidism in apparently euthyroid subjects who have autonomous thyroid tissue. In comparison with the cholecystographic agents which are taken up by the liver, the renally-excreted contrast agents used for angiography or intravenous urography are much less potent in producing these effects. The paradox of T4 excess with normal T3 may arise after cholecystography, either by an acute T4 increase in a euthyroid subject, or by normalization of T3 in hyperthyroidism, thus creating a diagnostic dilemma. The recent trend towards use of oral cholecystographic agents in the urgent management of hyperthyroidism, because of their effect on serum T3, needs to be regarded with caution in view of the risk that hyperthyroidism may eventually be worsened if synthesis of T4 is not effectively blocked. For this reason, contrast media should probably be used in the treatment of hyperthyroidism only in conjunction with conventional antithyroid drugs. A history of exposure to contrast media should be sought in any acute or unexpected exacerbation of hyperthyroidism, or when T4 excess is found without an increase in T3.

Environmental factors altering thyroid function and their assessment

Chronic ingestion of modest doses of dietary iodine, radiation, and polyhalogenated biphenyls (PCB's and PBB's) are environmental factors with known or suspected adverse effects on the human thyroid. Iodine consumption in the United States is approaching 1 mg daily for a large segment of the population. Data are reviewed which support the need for concern regarding the long-term adverse effects of dietary iodine on thyroid function, particularly in certain susceptible individuals. Environmental sources of radiation pose a significant risk of thyroid cancer and hypothyroidism under certain circumstances which may be intentional, inadvertent, or accidental. Exposure to polyhalogenated biphenyls during manufacture or as industrial pollutants are hazardous to man and to wildlife in moderate or large quantities and perhaps also in small amounts. The need to investigate the potential harm posed by these factors in the quantities commonly encountered is emphasized.

Iodine treatment of iodine-induced thyrotoxicosis

A 62-year-old female who had received prolonged iodine therapy for asthma presented with severe thyrotoxicosis and severe asthma. Her history, elevated serum thyroxine and triiodothyronine, low 131I uptake, and elevated intrathyroidal iodine content by fluorescent scan were most consistent wiht a diagnosis of iodine-induced thyrotoxicosis (IITT). The clinical course of her thyrotoxicosis was protracted, and in spite of its etiologic role in the precipitaton of thyrotoxicosos, iodine was therapeutically efficacious, although combined treatment with methimazole was required to ultimately restore euthyroidism. Therapy with lithium was also employed but appeared to be only transiently effective and combined no additional decrement in serum T4 than that seen with iodine alone. The case exemplifies the heterogeneity of what is considered "iodine-induced" thyrotoxicosis, the complexities inherent in establishing a diagnosis of IITT, and the use of other rapid acting pharmacologic agents in IITT when beta blockade is contraindicated by asthma.

Normal prolactin response following thyrotrophin releasing hormone in patients with autonomously functioning euthyroid multinodular goitre

Twelve female patients (mean age 60 years, range 41--74) with euthyroid multinodular goitre and a flat TRH test (median delta TSH 0.9 muIU/ml, range 0--3.5) had normal prolactin responses to TRH (median data prolactin 48 ng/ml, range 6--115). The results are comparable with those in euthyroid patients receiving full substitution doses of thyroid hormone without increasing T3 and/or T4 levels beyond the normal range.

[Conservative treatment of other forms of hyperthyroidism (author's transl)]

Patients with toxic nodular goiter have only a slight chance for spontaneous remission. The same is true for hyperthyroid decompensated autonomous adenomas and iodine-induced thyrotoxicosis (jodbasedow). We therefore recommend antithyroid drugs only for preoperative preparation or for the therapy administered between fractionated 131I doses. The latter is indicated in patients over 40 years of age with a small goiter. The risk of hypothyroidism is less than 1% according to the experiences of eight thyroid centers. Experiences with euthyroid autonomous adenomas suggest no specific therapy. These patients may be managed under most circumstances by periodic follow-up evaluations.

Effects of iodides on the hypothalamic-pituitary-thyroid axis in neurological endemic cretinism: evidence for compensated thyroidal failure in adult life

Thyroid function studies, performed after iodide administration to five patients with neurological endemic cretinism, were indicative of hypothyroidism. All five subjects had either a low serum thyroxine (T4) or a high basal thyrotrophin (TSH) level and a clearly exaggerated TSH response to thyrotrophin releasing hormone (TRH). These findings are in sharp contrast with those we have previously described in goitrous patients without cretinism from the same geographical area. One interpretation of our observations is that there is an underlying mild defect in thyroid hormone synthesis in endemic cretinism predisposing to iodine induced hypothyroidism.

The toxic effect of small iodine supplements in patients with autonomous thyroid nodules

In sixteen cases of toxic adenoma of the thyroid (autonomous hot nodule with complete suppression of the surrounding normal parenchyma) potassium iodide was given in doses of 100 microgram/day for one week, 200 microgram/day for another and 400 microgram/day for a third week. There was a progressive increase in the serum T4 level. Serum T3 also increased, although this was significant only after the first week. Serum TSH was undetectable throughout the entire period of the study. This metabolic pattern is different from the response seen in cases of nontoxic endemic goitre, where small iodine supplements induce an increase in serum T4 but a decrease in serum T3. Furthermore, the present results may explain the phenomenon of iodine-induced or iodine-precipitated hyperthyroidism (Jod-Basedow) when patients with autonomous thyroid are presented with a high iodine intake. In contrast to the results obtained with small iodide doses, two other cases treated with large pharmacological doses of iodide showed a decrease in both serum T4 and serum T3. It is concluded that the physician should be aware of the possibility of precipitating or aggravating thyrotoxicosis in patients with an autonomous hot nodule by increasing their intake of iodine.

Thyrotoxicosis induced by iodine contamination of food--a common unrecognised condition?

The incidence of thyrotoxicosis in northern Tasmania rose significantly in 1964, two years before an epidemic of iodine-induced thyrotoxicosis was precipitated by the addition of iodate to bread to prevent goitre. Each time older patients accounted for most of the increase. The 1964 increase was probably iodine-induced as the use of iodophor disinfectants on dairy farms, which causes iodine residues in milk, began in 1963 and a fall in the prevalence of goitre in young children suggested an increase in dietary iodine at about that time. A further small increase in thyrotoxicosis in 1971 may also have been iodine-induced as it followed an extension of the use of iodophors. Dietary iodine is rising substantially in many places because of high iodine levels in milk and the use of iodine compounds in automated bread making, and this may be causing unsuspected iodine-induced thyrotoxicosis. Dietary iodine should be monitored regularly and clinicans alerted to any rise. Contamination of common foods with iodine should be more strictly controlled.

Adverse effects of iodides on thyroid function

The administration of pharmacologic quantities of iodine such as iodides for the treatment of pulmonary disease, organic iodine present in medications and x-ray contrast dyes, and the ingestion of iodine-rich natural foods, may result in goiter, hypothyroidism, or hyperthyroidism, especially in patients with underlying thyroid disease. Medications containing iodide may induce hypothroidism in euthyroid patients with Hashimoto's thyroiditis, 131I or surgically treated Graves' disease, or following hemithyroidectomy for nodules; and they may induce hyperthyroidism in patients with endemic iodine-deficient goiter, autonomous nodules or nontoxic nodular goiter, or in patients recently treated with antithyroid drugs for Graves' disease. Rarely, hypothyroidism or hyperthyroidism may develop in patients with completely normal thyroid function during administration of iodide. The etiology of iodide-induced goiter and hypothyroidism in patients with cystic fibrosis remains obscure. Iodide-induced myxedema may also occur in patients receiving drugs which alter thyroid function, such as lithium, phenazone, and sulfisoxazole. Finally, iodides do have a role in the treatment of hyperthyroidism but their use should probably be restricted to thyroid storm, preoperative preparation of the hyperthyroid patient, and following 131I treatment.