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Safely treating an overactive thyroid


Q: My doctor has recommended treatment with radioactive iodine for an overactive thyroid gland. The thought of radioactivity scares me. I am only 35 and am especially afraid that the treatment may affect my ovaries and result in damage to my children if I should get pregnant again. Another concern is an increased risk of cancer. It would help me to know about the safety of radioactive iodine.

A: Radioactive iodine is the safest and most economical way to treat the common causes of an overactive thyroid (thyrotoxicosis). Radioiodine produces a permanent cure and avoids the possible complications of surgery on the thyroid gland.

At the time this form of therapy was introduced, there was concern that it might cause cancer, especially of the thyroid, or leukemia. However, many years of experience have shown no increased rate of thyroid cancer or leukemia.

Although apprehension about damage to the ovaries initially limited radioiodine use to women over 40, there is no evidence that children of women treated with radioactive iodine have an increased likelihood of genetic abnormalities. In fact, the usual dose of radioiodine delivers only a small amount of radioactivity

(roughly equivalent to that of a barium enema) to the ovaries.

If there is any chance you might be pregnant, you should have a test because radioactive iodine shouldn't be administered during pregnancy.

The major problem with radioiodine treatment is the subsequent occurrence of hypothyroidism (inadequate production of thyroid hormone). Although it develops at a higher rate during the first year or two after treatment, hypothyroidism continues to occur each year in 3 percent of all treated. As a result, after 10 years hypothyroidism is present in about half the people treated with radioactive iodine.

The good news is that hypothyroidism is readily and fully treated with one pill a day. The bad news is that hypothyroidism may go undetected because it can develop so slowly and subtly. Accordingly, radioiodine therapy requires long-term follow-up by your physician.

Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine and associate dean for faculty affairs at the school.

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