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

Desenvolvimento de um método para a determinação da iodúria e sua aplicação na excreção urinária de iodo em escolares brasileiros

Desenvolvemos método semi-automatizado em placa para a determinação de iodo urinário; utilizamos, primeiramente, a digestão das amostras de urina com persulfato de amônio e, a seguir, estimamos a quantidade de iodo pela redução do sulfato cérico amoniacal. O método foi validado no inquérito nacional de monitoração da deficiência de iodo, realizado em 1994, que empregou um sistema de amostragem mista da população brasileira e analisou a iodúria em 16.803 amostras de urina de escolares obtidas por coleta casual. Em 401 municípios estudados encontramos 4 com deficiência de iodo de grau moderado (Almas, Arraias e Paraná, em Tocantins, e Cocos, na Bahia) e 116 de grau leve. Desta forma, este estudo mostrou a presença de regiões com deficiência de iodo em 1994, a despeito do programa de iodação do sal. Dados recentes de outros autores, com número menor de municípios, indicam excesso de ingestão de iodo. Assim, num país de dimensões continentais e heterogêneo como o Brasil, é necessária a realização de avaliações periódicas de amplitude nacional para a verificação da ingestão de iodo da população. O método apresentado neste estudo apresenta as características de simplicidade e eficiência necessários para este tipo de estudo populacional.

Prevalence of thyroid dysfunction in patients with acute atrial fibrillation attended at a cardiology emergency room

CONTEXT

Atrial fibrillation occurs frequently in patients with thyrotoxicosis, while it has low prevalence in adults of the general population. The prevalence of thyroid dysfunction in subjects with atrial fibrillation is 0 to 24%, a wide variation that is attributed to the different methodologies applied. However, continuous use of amiodarone in patients with previous atrial fibrillation may interfere with these prevalence rates.

OBJECTIVE

In this study, we present the prevalence of thyroid dysfunction in adult patients who presented at a cardiac emergency room with acute atrial fibrillation, using a sensitive thyroid-stimulating hormone (TSH) assay and triiodothyronine (T3) and thyroxine (T4) determination.

TYPE OF STUDY

Cross-sectional study.

SETTING

Emergency room of a tertiary care facility.

PARTICIPANTS

A total of 72 patients with atrial fibrillation who presented at the emergency room not more than 48 hours after its onset.

PROCEDURES

A standardized questionnaire and 12-lead electrocardiogram were applied, and T3, T4 and TSH were determined.

MAIN MEASUREMENTS

TSH, T3 and T4 determination.

RESULTS

Among these patients, 16.6% had altered thyroid function tests: 6.9% had hyperthyroidism, 5.6% hypothyroidism and 4.2% had increased T4 levels, by means of amiodarone use.

CONCLUSION

The high prevalence of thyroid dysfunction in our study, especially hyperthyroidism, suggests that routine thyroid testing with sensitive thyroid-stimulating hormone assay is required in patients with acute atrial fibrillation.

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 and thyroid function]

Iodine is a raw material for the thyroid production of hormone which is on the major external control of TSH. The thyroid adaptation to iodine deficiency consists in an increasing iodine concentration from the circulation, an enhancing iodination of the tyrosyl residues in thyroglobulin, a decreasing iodine storage associated to a better recycling of non hormonal iodine and thyroid hyperplasia to provide more synthetic possibilities. Genetic variation and environmental factors explain the wide variation of individuals response to iodine deficiency resulting in a high prevalence of goiter, a mild TSH level increase or overt hypothyroidism. At long term iodine deficiency may have severe pathological consequences and induce neuropsychological deficits in school-children. A policy of iodine supplementation mainly by iodized salt must be undertaken in many areas in the world. Effects of an iodine excess on thyroid function are variable depending upon the underlying thyroid disorder and ambient iodine intake. The most subjects remain euthyroid by mechanisms of autoregulation based on an inhibition of thyroid hormone synthesis and a decrease in the thyroid iodide trap. Euthyroid individuals from high iodine intake areas or those with a history of lymphocytic thyroiditis, treated Graves' disease or subtotal thyroidectomy develop hypothyroidism. On the other hand iodine induced hyperthyroidism is more common in areas of iodine deficiency and in older patients with nodular goiter.

Amino Acid Composition of Proteins Extracted from Endemic Goiter Glands

Proteins were isolated and characterized in thyroid tissue of six patients from Brazil with endemic goiter. Biochemical studies of these thyroidal proteins included gel filtration, electrophoresis, and amino acid analysis. In addition to thyroglobulin, two of the most abundant proteins found in all goiters studied had molecular weights of 68 and 14 kDa. One protein was identified as albumin based on its immunoreactivity with antibodies to serum albumin. The other protein was identified as a hemoglobin subunit using reverse-phase high-performance liquid chromatography (H PLC). Identification was confirmed by partial N-terminal amino acid sequencing that showed several nonconservative differences in thyroid albumin when compared to human serum albumin (HSA). Biochemical findings were correlated with iodine and hormone contents in serum and thyroglobulin from these patients. Based on these findings, we suggest that hemoglobin and albumin are taken up from the blood by the hyperplastic thyroid tissue. Albumin would be processed by the thyroid follicular cell, becoming iodinated and released into the circulation.

Surgical significance of non-toxic iodine-avid goitre

During the period 1970-87, of 1580 patients operated on for non-toxic nodular goitre, 17 satisfied the laboratory criteria for iodine avidity. All of these goitres were non-endemic, with no evidence of enzymatic deficiency. Preoperative thyroxine markedly reduced the surgical morbidity by decreasing the size and vascularity of the gland.

Natural course of iodine-induced thyrotoxicosis (Jodbasedow) in endemic goiter area: a 5 year follow-up

In the Balsas region of North Brazil (85% prevalence of goiter), 1876 goitrous subjects (1663 with goiter grade I and II and 103 with grade III multinodular goiter) were treated with 1 ml of iodized oil im (l-oil). From the population with grade III goiter we were able to follow-up for 5 yr 13 euthyroid goitrous patients (group 1) and 8 goitrous individuals (group 2) who developed iodine-induced thyrotoxicosis (IIT, 0.42% of the total population or 7.76% of the multinodular goiter subjects). The two groups were matched for age and goiter size, and had no significant differences in the baseline levels of thyroid hormone concentration, T3/T4 ratio or mean serum TSH. However, group 2 had a higher concentration of serum Tg, and 48 h after challenge with 10 U of bovine TSH (bTSH) had a significantly higher absolute release of T3 and Tg than group 1. In 4 patients IIT was transitory and resolved by 12 months. Four other subjects, however, maintained a mild clinical form of IIT that only normalized at 50 months. Only one patient needed treatment with methylmercaptoimidazol. There was no evidence of autoantibodies (TSH-receptor inhibiting antibody, anti-Tg or anti-microsomal antibodies) against thyroid antigens in group 2 patients. All subjects, including those with thyrotoxicosis, showed a remarkable shrinkage of the goiter by 60 months which was reflected by a significantly lower absolute response of T3 and Tg after bTSH.(ABSTRACT TRUNCATED AT 250 WORDS)

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)