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In addition to medications and surgery, radioactive iodine is a treatment option for hyperthyroidism.
Radioactive iodine is used to treat approximately 90% of the hyperthyroid patients in the United States. Radioactive iodine is taken orally and absorbed by the thyroid gland. Once in the gland, it gives off radiation that damages the thyroid cells and slows the thyroid hormone production. The radioactive iodine that is not taken up in the thyroid leaves the body within two or three days, primarily through the urine.
Calculating the correct dose of radioactive iodine is complicated and thus done by a trained specialist. The biological effects of radiation vary among different people, and the length of time it takes to "cure" hyperthyroidism varies greatly as well. This treatment is usually effective in up to 90% of patients with Grave’s disease after two months, but in some patients it may take as long as six months. A few patients may require a second or even third treatment. This happens more commonly in men and patients under the age of 40 years. After treatment with radioactive iodine, the size of the thyroid gland will be reduced by 40% in patients with toxic multinodular goiter.
The side effects of radioactive iodine treatment include the following:
Most people who have hyperthyroidism become hypothyroid in five to ten years. This may happen if the hyperthyroidism has not been treated or if the treatment was antithyroid medication or surgery. Hypothyroidism may develop as early as two months or as late as 20 years after treatment for hyperthyroidism. For this reason, many doctors favor destroying the thyroid altogether. The risk of hypothyroidism after radioactive iodine treatment is 10%-20% in the first year and 5% per year for every year after. Because of this, it’s important to see your doctor frequently during the first year and have annual thyroid function testing thereafter.
Special Considerations
References:
American Association of Clinical Endocrinologists website. Available at: http://www.aace.com/ .
American Thyroid Association website. Available at: http://www.thyroid.org/ .
Bonnema SJ, Bartalena L, Toft AD, Hegedus L. Controversies in radioiodine therapy: relation to ophthalmopathy, the possible radioprotective effect of antithyroid drugs, and use in large goiters. Eur J Endocrinol. 2002;147:1-11.
Harrison’s Principles of Internal Medicine. 14th ed. McGraw Hill; 2001.
National Graves’ Disease Foundation website. Available at: http://www.ngdf.org/ .
Pearce EN. Diagnosis and management of thyrotoxicosis. Brit Med J. 2006;332:1369-1373.
Thyroid Foundation of Canada website. Available at: http://www.thyroid.ca/ .
Last reviewed November 2008 by David Juan, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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