TRANSIENT THYROTOXICOSIS IN ENDEMIC GOITRE PATIENTS FOLLOWING EXPOSURE TO A NORMAL IODINE INTAKE

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Abstract
Endemic goitrous subjects (23) (goiter grade: III and IV) that were living in a chronic I deficient area (I intake: < 40 .mu.g I/day) were submitted to clinical and laboratory evaluation within 3-8 wk of arrival at the metropolitan area of Sao Paulo, Brazil, where daily I intake is estimated to be 150-200 .mu.g I/day. Eight patients developed a mild thyrotoxic state (T4 [thyroxine] = 14.7 .+-. 2.3 .mu.g/dl, T3 [triiodothyronine] = 279 .+-. 55 ng/dl, no TSH response to TRH). Five additional subjects, although euthyroid, had a blunted TSH-response to TRH, and the remaining 10 patients were euthyroid and had a normal TSH response to TRH. Thyrotoxicosis was associated with larger goiters (mean thyroid wt: 133 .+-. 46 g), with high thyroid uptake of RAI [radioactive I] (mean 24 h 131I uptake: 40 .+-. 15%) but not with increased urinary I excretion. Serum Tg [thyroglobulin] levels were more elevated in the first 2 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 3-6 mo. without the need for any specific medication. Thus, a relatively small and normal I intake due to regular consumption of iodized salt and industrialized foods may induce a transient form of thyrotoxicosis in endemic goiter patients arriving into urban areas.

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