Veterinary Q&A: Hyperthyroidism in cats

SeattleTimes

August 24, 2011

Posted by Neena Pellegrini

Dr. Deborah Carlson, a veterinarian at Pilchuck Veterinary Hospital in Snohomish, answers this week's question.

Question:My 15-year-old male cat has been diagnosed with hyperthyroidism. I have been informed of the three choices available to me. I am leaning toward the radioactive iodine treatment, because it is essentially a cure. But what are the risks and drawbacks associated with this procedure? I want to prolong his life, but I want it to be a good quality of life.

Answer:Hyperthyroidism is one of the most common diseases seen in geriatric cats.

Unlike some of the other geriatric disease seen in cats, hyperthyroidism is a curable disease. I always tell my clients that if I had to pick a disease for my cat, it would be hyperthyroidism. In fact, two of my own cats have been treated successfully with radioactive iodine.

Taking a step back, let's look at what causes hyperthyroidism and what its symptoms are.

Hyperthyroidism is caused by a benign tumor of the thyroid gland called an adenoma. The tumor cells secrete excessive thyroid hormone, causing an increase in your cat's metabolism. This could lead to an increased appetite and increased water intake, weight loss despite a ravenous appetite, behavior changes, vomiting, diarrhea and an increased heart rate.

If left untreated, your cat eventually would develop heart and kidney disease and high blood pressure, which could lead to blindness, vascular events (stroke-like episodes) and sudden death.

There are three options to treat hyperthyroidism. I'll review the pros and cons of each.

Option one:  Radioactive iodine. This is my preferred-treatment option because it would cure the disease. Your cat would be given an injection of radioactive iodine, which would destroy the tumor cells but not the healthy thyroid tissue.

Pros:

a. It would be a painless, noninvasive procedure in which your cat would be given an injection through an intravenous catheter.

b. It would cure your cat from the disease. It also would stop or reverse any changes that have occurred to the heart muscle.

c. Your cat would not require anesthesia.

Cons:

a. Your cat would have to visit a special hyperthyroid clinic and would need to stay for around two to five days in the hospital. We are fortunate to have two excellent clinics in the South Sound area -- in Shoreline and Tacoma that have the special certifications needed to handle radioactive iodine. You would not be able to visit your cat during this time.

b. There would be a financial commitment because treatment would not be inexpensive. On average, the procedure would cost approximately $850 to $950.

c. You would need to confine your cat indoors (or allow supervised outdoor outings) for approximately two weeks. You would need to use a special flushable litter for three months or so after your cat is treated.

Option two:  Medical management. The medication methimazole would be used to treat hyperthyroidism. It would control, but not cure, your cat's disease.

Pros:

a. Your cat would not need to visit a special clinic. Your veterinarian could prescribe the medication for you.

b. It is the treatment of choice for cats that are not candidates for radioactive iodine.

Cons:

a. You would need to give your cat a pill twice a day for the rest of his/her life. Anyone who has ever attempted to give a cat a pill knows how difficult this can be. Many cats are pessimists at heart and are much less likely than dogs to accept a tasty morsel wrapped around a pill.

b. There are several potential adverse reactions to the medication, including vomiting, poor appetite, lethargy, bone-marrow disorders, bleeding and allergic skin reactions. The medication would not stop or reverse the effects of hyperthyroidism on the heart muscle.

c. The cost of the medication plus the frequent required bloodwork monitoring would end up being more expensive than the radioactive iodine treatment, and your cat would not be cured.

Option three:  Surgery. Your cat would be anesthetized and both thyroid glands would be removed. I rarely consider this option for my patients because of the increased risks compared with radioactive iodine or medical management.

Pro: a. It is one of the treatments recommended for malignant thyroid tumors.

Cons:
a. Your cat would require anesthesia, and many cats with hyperthyroidism have increased risks of anesthetic complications.

b. It would be expensive and requires a veterinarian skilled in soft-tissue surgery.

c. Your cat would most likely require thyroid-supplement pills for the rest of his/her life. The cat could also require calcium supplements.

I hope this helps with your decision on how to treat your cat's hyperthyroidism. I wish you and your cat many happy, purrfect years together.

Dr. Deborah Carlson

Carlson joined Pilchuck Veterinary Hospital in Snohomish in June 2011. She received an undergraduate degree in zoology from the University of California, Santa Barbara in 1996 and a veterinary degree from Colorado State University in 2000. Her special interests include internal medicine, complementary and alternative medicine, feline care and pain management. She owns three golden retrievers.