Radioiodine Therapy – The Best Treatment for Feline Hyperthyroidism

What is hyperthyroidism?

The Thyroid glands sit on either side of the voice box. They produce hormones that control the body’s metabolism (e.g., how fast food calories are burned, how much inhaled oxygen is used, and how rapidly the heart beats). In other words, how fast your cat’s “engine is revving” depends on how much thyroid hormone is produced. Older cats often develop a benign growth in one or both thyroid glands, resulting in excessive hormone production.

What are the signs of hyperthyroidism?

Hyperthyroid cats tend to lose weight despite a ravenous appetite. They may drink excessive amounts of water, have diarrhea, vomit intermittently, and become hyperactive or irritable. The heart rate is elevated and sometimes irregular. Your veterinarian may be able to hear a heart murmur and feel an abnormal nodule in the thyroid region.

Diagnosing hyperthyroidism

Your veterinarian can do a blood test to measure the thyroid hormone level. Confirming hyperthyroidism is very important because other problems such as diabetes, heart disease and inflammatory bowel disease can mimic the signs of hyperthyroidism. Older cats may have multiple health problems, so a complete physical examination, blood work and urine screening are always indicated prior to treatment.

What is the treatment procedure?

A recent physical examination, blood work and urine testing are required to rule out concurrent diseases. If a heart problem is suspected, chest x-rays and an echocardiogram are recommended. Any unrelated health issues should be stabilized prior to admission; if necessary a consultation with Dr. Franklin can be arranged. After the radioiodine injection, your cat is boarded in a shielded medical ward until the radioactivity level fades (four days). All cats have their own oversized cage facing large windows to the outside so they can indulge in one of their favorite activities. They are given fresh food and water twice daily. You are welcome to provide favorite foods as well as any medication or nutritional supplements. Because bedding and toys could become contaminated during hospitalization, they cannot be returned to you if you provide them. You can call everyday for an update of your cat’s condition.

Will my cat be radioactive?

Yes, but only temporarily because the iodine is eliminated in the urine and feces. Once your cat is released, there are some limitations on your interaction with your cat and special handling procedures of his/her litter. Detailed instructions will be provided.

Can I visit my cat during hospitalization?

We are sorry but State regulations do not permit visitors in the radioiodine therapy room.

Are there any complications?

Radioiodine therapy does not have any of the risks associated with surgical or medical treatment.  In about five percent of cats, the hormone level may stay high and require re-treatment, which is done at no extra cost. Occasionally hormone levels do become too low after radioiodine treatment. If this should occur,  your cat would require supplementation with oral thyroid hormone.

What follow-up is necessary?

Thyroid levels and Urine Specific Gravity should be measured at 1, 3 and 12 months post-treatment by your regular veterinarian.
If you have any questions about this information or would like to schedule an appointment, please contact Oregon Veterinary Specialty Hospital at 503.292.3001.