Hyperthyroidism with a low radioactive iodine uptake

Abstract

To the Editor.— In small doses, inorganic iodide can function to inhibit thyroglobulin proteolysis. In larger doses, it can also block iodination of tyrosine residues within the thyroglobulin molecule. In either case, a hypothyroid state can be induced (Wolff-Chaikoff effect), which is usually transient and subject to escape. This escape phenomenon is not universal. Individuals who have abnormal thyroid tissue (autoimmune thyroiditis, or acquired after radioactive iodine therapy) often will remain hypothyroid with inorganic iodide treatment. 1 Amiodarone therapy may also result in prolonged hypothyroidism. Iodide administration may therefore cause a persistent decrease in thyroid hormone production. 2 More frequently, 3 iodide has also been shown to induce thyrotoxicosis (iod-Basedow effect) and cause immunologic aberrancies. Iodide treatment of hyperthyroidism will not achieve euthyroidism in up to 25% of individuals. 2 The radioactive iodine uptake in this group will remain low due to a dilutional effect from the exogenous iodide, despite