The effect of iodized oil on the TSH response to TRH in endemic goiter patients

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.

Iodine-induced hyperthyroidism in a patient with a normal thyroid gland

Iodine-induced hyperthyroidism can develop even in the presence of an otherwise normal gland. One of the less common sources of iodine is tablets of seaweed, sold over the counter without prescription. We report the case of a 72 year old female who developed clinical and laboratory evidence of hyperthyroidism while ingesting sea-kelp (Vitalia) tablets. Six months after stopping the tablets, the symptoms and laboratory evidence of hyperthyroidism had disappeared. No evidence of pre-existing thyroid disease was found.

Long-term effect of iodized oil on serum thyroglobulin levels in endemic goitre patients

Serum thyroglobulin (Tg) response to bovine TSH (bTSH) was evaluated in 44 goitrous patients (grades III and IV) living in conditions of chronic iodine (I) deficiency (iodine urinary excretion less than 40 micrograms I/g) and in 26 normal subjects. After the initial clinical evaluation and laboratory tests (bTSH test, T4, T3, anti-Tg and anti-microsomal antibodies) all goitrous patients received 1 ml i.m. of iodized oil (I-oil) and were followed up for 30 months. The bTSH test was repeated at 6, 12, 20 and 30 months after I-oil in 21 subjects. A marked reduction in goitre size was observed in 85% of the patients with a concomitant significant increase in the mean serum T4 and T3 concentrations, a significant fall in the mean serum TSH level and a significant decrease in the T3/T4 ratio. Goitrous patients had elevated serum basal Tg levels (55 +/- 8 SEM micrograms/l) and a significantly mean higher peak Tg value after bTSH (200 +/- 65 micrograms/l) as compared with normal subjects (respectively, 11 +/- 1.4 and 32 +/- 3.4 micrograms/l). Larger goitres (grade IV) had a significantly higher mean peak Tg response as compared with grade III goitres. Treatment with I-oil significantly reduced the mean peak Tg response to bTSH after 6 months (59 +/- 10 micrograms/l) but at 12 and 20 months the peak Tg response after the injection rose, respectively, to 110 +/- 19 micrograms/l and 92 +/- 14 micrograms/l (P less than 0.02 as compared with 6 months), returning to the normal range only at 30 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient thyrotoxicosis in endemic goitre patients following exposure to a normal iodine intake

Twenty-three endemic goitrous subjects (goitre grade: III and IV) that were living in a chronic iodine-deficient area (iodine intake: less than 40 micrograms I/d) were submitted to clinical and laboratory evaluation within 3-8 weeks of arrival at the metropolitan area of São Paulo, where daily iodine intake is estimated to be 150-200 micrograms I/d. Eight patients developed a mild thyrotoxic state (T4 = 14.7 +/- 2.3 micrograms/dl, T3 = 279 +/- 55 ng/dl, no TSH response to TRH). Five additional subjects, although euthyroid, had a blunted TSH-response to TRH, and the remaining ten patients were euthyroid and had a normal TSH response to TRH. Thyrotoxicosis was associated with larger goitres (mean thyroid weight: 133 +/- 46 g), with high thyroid uptake of RAI (mean 24 h 131I uptake: 40 +/- 15%) but not with increased urinary iodine excretion. Serum Tg levels were more elevated in the first two groups of patients (respectively, geometric means 68 and 72 ng/ml), than in the euthyroid, TRH-responsive group (52 ng/ml). Thyrotoxicosis resolved spontaneously after three to six months without the need for any specific medication. It was concluded that a relatively small and normal iodide intake due to regular consumption of iodized salt and industrialized foods may induce a transient form of thyrotoxicosis in endemic goitre patients arriving into urban areas.

Congenital goitre and hypothyroidism with impaired iodide organification and high thyroid peroxidase concentration

A sibship of thirteen subjects whose parents were first cousins was studied for a defect in thyroid hormone synthesis. Five sibs were goitrous and had congenital hypothyroidism. All but one showed a positive perchlorate discharge test (PDT). Three other subjects were goitrous and euthyroid (one with a positive PDT), and the remaining five sibs were euthyroid with a presumably normal thyroid. However, an abnormally exaggerated TSH response to TRH was observed not only in the hypothyroid patients but also in six of the other subjects, indicating a decreased thyroid feedback at the pituitary level in the presence of a normal serum concentration of thyroid hormones. In two hypothyroid patients a normal serum T3, low serum T4 and a low reverse T3 were observed. Microscopic studies of thyroid tissue from three of the sibs disclosed marked cellular hyperplasia with no lymphocytic infiltration anywhere in the tissue. Peroxidase activity was determined on tissue from three sibs by three different assay procedures. It was within the normal range in one patient and was significantly elevated in the other two. There was no evidence for a qualitatively defective peroxidase. The defect in thyroid function in this family does not appear to involve a peroxidase deficiency. Thyroglobulin isolated from the thyroid glands of two of the goitrous, hypothyroid subjects was poorly iodinated but was judged to be normal by immunoreactive and ultracentrifugation procedures. Although the nature of the thyroid metabolic defect in this family was not elucidated, the evidence suggests a genetic defect, probably involving a recessive gene.

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.