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Hyperthyroidism is a condition that results from secretion of excess thyroid hormone. Hyperthyroid cats usually develop adenomatous hyperplasia or adenoma (benign tumor) of the thyroid gland (located in the neck). Thyroid carcinoma (malignant tumor) occurs rarely in cats.


Radioiodine (radioactive iodine) will likely cure the hyperthyroid condition and is a good non-surgical option. The procedure for this treatment is relatively simple, consisting of a single dose of radioactive iodine.

About radioiodine treatment

Iodine is an element required for normal health. In the body it is used primarily by the thyroid gland to produce thyroid hormones.  Radioiodine (I-131) is a form of iodine that has been made radioactive. In its radioactive state it undergoes a natural process (decay) during which it gives off radiation.

When taken into the body, a significant percentage of radioiodine accumulates in the thyroid gland. The remainder of the I-131 is excreted in the urine and feces. The radiation selectively destroys the thyroid tumor cells and thus treats the hyperthyroid condition.

The radioiodine is given as a single injection on the first day of hospitalization. After the treatment is administered, the patient is placed in isolation and monitored until his or her radioactivity level is low enough to permit release from the hospital, which is usually five to seven days.


Studies have shown that a single dose of radioiodine is effective in curing hyperthyroidism in more than 94% of patients. Even cats that are not completely cured after one treatment will show a relative decrease in their circulating thyroid hormone concentrations and improve clinically.  Most cats that remain hyperthyroid after the first treatment are generally cured by the second treatment.

For more information on this treatment, please contact AVC at (801) 942-3951.