Associated Veterinary Specialists - Advanced Veterinary Care - St. Louis, MO
Specialized St. Louis Veterinary Services AVS Veterinary News

AVS Treatment for Hyperthyroidism in Cats

To date, AVS has treated over 700 cats diagnosed with hyperthyroidism, with radioactive iodine-the gold standard for therapy of these cats. When compared to other methods of treatment, radioactive iodine is by far the safest and most effective.

The majority of our cats arrive with a diagnosis of hyperthyroidism. Therefore we do a history and physical exam to confirm the diagnosis and establish the radioactive iodine dose.

These cats receive a filter sterilization subcutaneous injection (just under the skin) on Tuesday morning. Our staff is here 24 hours while they are hospitalized to monitor them. They are released on Thursday.

We ask these cats' owners to follow some simple, specific guidelines about handling the cat for 2 weeks after therapy. Owners are provided with oral and written explanation of these expectations.

Two weeks after treatment the cat will return to AVS for a Geiger counter check and four weeks after should return to their referring veterinarian for a follow-up T4 blood test. These results will be sent to us for our files.

Alternative therapies for treatment of hyperthyroidism exist. Surgery can be performed to remove the abnormal thyroid tissue but has the obvious drawbacks of anesthesia or surgical complications, the development of hypocalcemia because of damage to the parathyroid gland and a 15 to 20% recurrence rate. In the opinion of the specialists at AVS, surgery is never appropriate in communities that have radioactive iodine available.

The antithyroid drug methimazole is available as a prescription medicine. Its effect is to impair release of thyroid hormones from the gland. It is effective for some cats. Methimazole has several drawbacks that dictate it should only be used in select cases. The drug must be purchased and is not inexpensive. It must be administered to an animal that typically dislikes any oral medication. Topical formulations are of limited bioavailability and are even more expensive than oral. Methimazole frequently causes side effects of vomiting, skin, blood and liver problems that require discontinuation of the drug. It must be monitored frequently. When compared to cats treated with methimazole, cats treated with radioactive iodine live on average twice as long. Some veterinarians recommend a trial of methimazole prior to radioactive iodine therapy, however experts in the field find this to be necessary in only selected cases that have other medical conditions such as kidney failure.

A new Hill's diet, Y/D, has recently been marketed for cats with hyperthyroidism. The diet is deficient in iodine and has been shown to decrease thyroid hormone levels in affected cats. This diet may be appropriate for very old cats or cats with preexisting life threatening medical conditions. It should only be used in homes where one cat lives.

The following graph demonstrates the cost vs time of various treatments for hyperthyroidism to demonstrate the cost effectiveness of radioactive iodine. When each of these treatments is provided and monitored by standard expert recommendations a break even point is clearly seen. For cats treated with methimazole the time is about 18 months and for Y/D it is about 27 months. Most of the initial resistance to using radioactive iodine is based on cost of administration but when evaluated over time it is not only the most effective and safest therapy, it is also the most cost effective.