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.