Medical Health Encyclopedia

By the end of 5 years, about 65% of treated patients have developed hypothyroidism, after which the rate of this condition levels off to about 1% a year. Such patients need to take thyroid hormones for the rest of their lives. Other forms of treatment for overactive thyroid glands using either antithyroid drugs or surgery may also result in hypothyroidism.

Iodide Abnormalities

Too much or too little iodide can cause hypothyroidism. If there is a deficiency of iodide, then the body cannot manufacture thyroxine. About 200 million people around the world have hypothyroidism because of insufficient iodine in their diets. Too much iodide is a signal to inhibit the conversion process of thyroxine to T3. The end result in both cases is inadequate production of thyroid hormones. Some evidence suggests that excess iodine in fact triggers the process leading to Hashimoto's thyroiditis.

Thyroid Surgery

Complete removal (total thyroidectomy) of the thyroid to treat thyroid cancer requires a lifetime of treatment with an appropriate dosage of thyroid hormone. Removing one of the two lobes of the thyroid gland (hemithyroidectomy), usually because of benign growths on the thyroid gland, rarely produces hypothyroidism. The remaining thyroid lobe will generally enlarge so that it can produce sufficient amounts of thyroid hormone for normal function. Many doctors recommend thyroid hormone treatment, however, to prevent the formation of additional nodules.

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A small percentage of Graves' disease patients who require surgery to remove most of both thyroid lobes (subtotal thyroidectomy) may develop hypothyroidism. It is important to find an experienced surgeon for this procedure and to have the thyroid checked at 6- or 12-month intervals.