Answer to Question #2450 Submitted to "Ask the Experts"

Q

Please advise me if I have a choice between radioiodine and an operation for hyperthyroidism. Which one is safer or more effective?

A

I have been asked to respond to your question about surgery compared with radioiodine therapy for hyperthyroidism. I am a nuclear medicine physician and radiation biologist with a specialty in nuclear medicine therapy. I have treated a few thousand hyperthyroid patients with radioiodine.

The use of radioiodine therapy is slightly safer and somewhat more effective than is the use of surgery for hyperthyroidism. Radioiodine therapy is regarded as the treatment of choice in this country, and I agree with that.

Before the Second World War, surgery was the only definitive treatment for hyperthyroidism. When iodine-131 became available after the war, it rapidly replaced surgery as the therapy of choice. Today, surgery for hyperthyroidism is rarely performed in the United States, but it is performed in third-world countries that cannot afford the radioiodine.

The surgical technique is to take out most, but not all, of the thyroid gland. This is done to avoid damage to the parathyroid arteries and the recurrent laryngeal nerves, which are easy to injure or destroy if one tries to remove every bit of the thyroid gland. The parathyroid arteries feed the parathyroid glands, which are necessary for blood calcium control and normal nerve and muscle function. If blood calcium levels are very low (such as from nonfunctional parathyroid glands), nerves and muscles do not function properly. Very low calcium levels can be fatal. The recurrent laryngeal nerves control speech. If one is cut, you will be permanently hoarse. If both are cut, you will be unable to speak at all. The other reason to leave a small amount of thyroid tissue is to allow the patient to have some thyroid function. A complete lack of thyroid function will be fatal. While thyroid hormone replacement pills are cheap and readily available in the United States, some third-world countries cannot afford them, so the patients need to have some thyroid tissue left.

Other than the risks of anesthesia and the risks to the parathyroid glands and laryngeal nerves discussed above, the remaining thyroid tissue tends to grow back, creating hyperthyroidism once again.

Radioactive iodine (¹³¹I, sodium iodide) is concentrated in thyroid glands, especially in hyperactive portions of the gland. For the type of hyperthyroidism called Graves' disease, it is usual for about 40-80% of the administered activity to concentrate in the thyroid gland. For functioning adenomas ("hot nodules"), the uptake is closer to 20-30%. Excess iodine-131 is excreted rapidly by the kidneys. The quantity of radioiodine used to treat hyperthyroidism is not enough to injure any tissue except the thyroid tissue, which slowly shrinks over a matter of weeks to months. If the first treatment is not enough to shrink the thyroid gland, we simply give another dose, usually about four months after the first. We do not use radioiodine in pregnant or lactating women, as it can destroy the fetal or infant thyroid. Radioactive iodine is either swallowed in a capsule or sipped in solution through a straw. It is an outpatient procedure. There are some simple radiation safety precautions necessary for about a week (it varies with the patient and the dose).

The goal of therapy in Graves' disease is to destroy the whole gland and then take thyroid hormone pills (one a day) to maintain normal thyroid function. Untreated, Graves' disease will "burn out" the thyroid gland (the disease is a chronic inflammation), so treatment with radioiodine merely accelerates the pathological process. The goal of therapy with "hot nodules" is to ablate the hyperthyroid areas, leaving normal areas to function normally afterwards, usually without the need for hormone replacement (unless the gland has numerous "hot nodules").

I hope you now understand why I believe that radioiodine therapy for hyperthyroidism is better than surgical therapy. If you have other questions that I have not covered, please ask.

Carol S. Marcus, PhD, MD
Professor of Radiation Oncology and of Radiological Sciences, UCLA