Complete iodide trapping defect in two cases with congenital hypothyroidism: adaptation of thyroid to huge iodide supplementation.

Two cases of congenital defect in iodide trapping mechanism are related. The absence of thyroid and gastric concentration of 99mTcO4 led to the diagnosis. The study of saliva and gastric:serum concentration ratios confirmed the complete defect. The kinetics of radioiodine studied by external detection showed an early simultaneous decay in the thyroid, the stomach and the left ventricle. Thyroid accumulation of 131I, demonstrated by camera imaging, was estimated to be 0.1% at 48 h. It probably originated from simple diffusion. Iodide supplementation was progressively increased to 4.5 g and 10 g day-1 respectively. It resulted in a normalization of all parameters. Huge doses of iodide did not result in any evidence of hyperthyroidism as TSH rose normally after TRH. Intermittent iodide supplementation in one case could not maintain euthyroidism longer than a few weeks. Daily treatment, therefore, seems necessary.

Iodine-induced thyrotoxicosis: analysis of eighty-five consecutive cases.

Iodine-induced thyrotoxicosis was documented in eighty-five cases. Eighty per cent occur in apparently normal thyroid glands; 60% among them occur in males. Amiodarone accounted for 50% of iodine-induced thyrotoxicosis. Mean thyroid hormone levels at diagnosis were: FT1: 21.7 (normal mean: 7.5, arbitrary units); T3: 4.53 nmol 1(-1) (normal: 2.30 nmol 1(-1). Mean 131I- 24-h uptake was 3.5% (normal range in France 25-45%) and was activated by exogenous TSH (mean 27%). The spontaneous cure in nontreated cases was observed within an average 6 months. A phase of biological hypothyroidism (mean FT1: 3.7, T3: 1.23 nmol 1(-1), TSH: 9.6 microU ml-1 (normal TSH range: 1-7 microU ml-1] preceded the return to euthyroidism. Intrathyroid iodine content measured by X-ray fluorescence was high, then fell gradually. Thyroid tissue study showed a large quantity of intrathyroid iodine and the overiodination of thyroglobulin. Histological and electron microscopic studies are reported. Prednisone and in some cases propylthiouracile were found to be effective.

[Congenital hypothyroidism with probable anomaly of thyroid receptiveness to thyrotropin. 2 cases]. / Hypothyroïdie congénitale avec probable anomalie de la réceptivité thyroïdienne à l'hormone thyréotrope. Deux observations.

Congenital hypothyroidism associated with unresponsiveness to thyrotropin (TSH) is a very rare condition. In the two cases reported the thyroid gland was not enlarged and endogenous THS secretion control was normal: the high TSH levels observed during hypothyroidism returned to normal after thyroid hormone replacement therapy and were normally responsive to TRH stimulation. Thyroid iodide clearance was investigated under various conditions of stimulation and inhibition. In hypothyroidism clearance was normal and TSH levels very high. During replacement therapy clearance seemed to be inversely correlated to levels of circulating thyroid hormones; it was almost nil in euthyroidism. Whatever the level of circulating hormones, clearance was not reactivated by exogenous TSH. In one patient in euthyroidism clearance, which was virtually zero, was unmodified after butyric AMPc stimulation, which suggests that the anomaly lies below the AMPc stage.