Radioiodine Therapy

AMC_LetterWhat is Hyperthyroidism?

Hyperthyroidism is a condition that results from the secretion of excess thyroid hormone.  Like an engine, the thyroid gland regulates many aspects of the body’s metabolic rate. Your Hyperthyroid cat has a tumor (98% are benign) that is producing too much thyroid hormone, which in turn keeps the cat’s “engine” running at an abnormally high speed. This condition over-stimulates virtually every organ system and causes reactions including behavioral changes, weight loss, excessive or decreased appetite, hyperactivity or lethargy, fever, rapid heartbeat and/or arrhythmia, shedding, increased water consumption and litter box output, diarrhea and osteoporosis. While fatal if left untreated, Feline Hyperthyroidism is now curable. In fact, it’s a one shot deal!


There are a variety of ways to treat this disease, including radioactive iodine therapy, medication, surgery or prescription diets. Your veterinarian will discuss the pros and cons of each treatment and help you make the best choice for your cat.

About Radioiodine Treatment

Iodine is an element required for normal health. In the body it is used primarily by the thyroid gland (located in the neck) 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. The radiation omitted consists of two types; beta and gamma. The half-life of I-131 is eight days; in other words, one-half of the radioiodine goes through this decay process every eight days.

When taken into the body, a large percentage of radioiodine accumulates in the thyroid gland. The remainder of the I-131 is excreted in the urine and feces. Once the radioiodine is taken up by the thyroid gland (or thyroid tumor in a hyperthyroid cat), the gamma rays and beta particles are released. The beta particles travel a maximum of 2-5 mm in tissue. Therefore, beta-particles are locally destructive but spare adjacent normal thyroid tissue, parathyroid glands and other cervical structures. The radiation selectively destroys the thyroid tumor cells and thus treats the hyperthyroid condition.

The radioiodine is given as a single dose on the first day of hospitalization. After the treatment is administered, the patient is placed in isolation. The patient is monitored at the hospital for a few days until its radioactivity level is low enough to permit release from the hospital, which is determined by state and federal regulation. By law, visitation is not permitted. During their stay, the cats are monitored by a licensed full time veterinary team. If you wish, you may call us to check on the status of your cat. It is routine for us to call each owner with daily progress reports.