Feline Hyperthyroidism

Hey Doctor… I Have a Question!

In this column, I will attempt to answer some of the most commonly asked questions we get in the exam room about a particular disease or illness. This issue’s topic: Feline Hyperthyroidism

Q: What is hyperthyroidism?

A: Hyperthyroidism is a disease caused by excessive production of thyroid hormone from the thyroid gland. The thyroid gland controls the body’s rate of metabolism so when it starts to produce excess hormone, the rate of metabolism speeds up. It tends to occur in middle-aged to older cats of any breed or sex. Dogs rarely get this disease.

Q: If metabolism is increased, what signs will I see in my cat?

A: Weight loss is a very common sign, even though your cat may be eating well. As the disease progresses over several weeks to months, you may notice increased thirst and urination, vomiting and/or diarrhea, hyperactivity/restlessness, weakness and an increased heart rate.

Q: If I notice one or more of these signs, what should I do next?

A: Since other diseases such as diabetes and chronic renal failure can have these same signs, it is always best to bring in your cat as soon as you notice them so we may quickly diagnose and start treatment. Hyperthyroidism is diagnosed by feeling for an enlarged thyroid gland in the neck and some simple blood tests.

Q: Is this disease fatal?

A: If not treated, this disease results in emaciation and severe metabolic and cardiac dysfunction. Yes, it can be fatal in this instance. The good news is that 98% of the time the thyroid gland enlargement is not due to cancer. Therefore, it is very treatable, even curable. The aim of our treatment is to decrease the excessive production of thyroid hormones as quickly as possible.

Q: How do you do that? What treatment options do I have?

A: There are three main ways of treating hyperthyroidism. They are oral medication, surgery and radioiodine therapy.

The oral medication we use is methimazole and it acts to block the production of thyroid hormone. If this option is chosen, you must give the medication life-long, usually twice daily for best results. Most cats tolerate methimazole well but frequent bloodwork is needed to adjust the dose and monitor for side effects. The medication will control the disease but not cure it.

If your cat is stabilized on methimazole and has minimal to no other health problems, you may elect for one of the other two treatment options that can be curative. Removal of the hyperfunctioning thyroid tissue (thyroidectomy) can lead to a cure in most patients. Relapses can be seen if hyperfunctioning tissue is left behind or there is thyroid tissue inaccessible to the surgeon (for example, in chest cavity).

Radioiodine therapy can also be curative with a low incidence of side effects. A radioactive isotope is used to destroy the hyperfunctioning tissue in the gland as well as in other places, such as in the chest cavity as mentioned previously. Normal thyroid tissue is not affected. Radioiodine therapy is locally destructive and doesn’t harm other parts of the body. This procedure is safe and effective with minimal stress to the patient. It is the most expensive option, but in the long run, it is cost effective and least traumatic.

The most important thing to remember as your pet ages is that many diseases start slowly and can be very subtle. We encourage twice yearly exams for our older patients as well as bloodwork to screen for these diseases. Early detection is best!

Dr. Christy Collignon

Just a quick reminder about holiday pet dangers.

Christmas trees: Make sure your tree is well-secured if you have a large dog or tree-climbing cat. Ingested pine needles can puncture your pet’s intestines so clean around the tree often. Drinking the water around the base of the tree can cause vomiting, diarrhea, mouth sores and loss of appetite.

Ornaments: Keep these out of your pet’s reach. Tinsel icicles, hooks, ribbons, rubber bands and breakable ornaments can be ingested causing serious or even fatal digestive problems.

Plants: Juice from poinsettias is toxic and can cause serious harm or even death. Vomiting, crying, frothing, pawing at the mouth and depression are all signs of plant poisoning.

Candy: Candy can cause upset stomachs which leads to vomiting and diarrhea. Remember, chocolate contains theobromine, a caffeine-like substance that acts like a stimulant and can be fatal in small doses.

Bones: Never give ham, poultry or steak bones to your pet. Ingestion of these can lead to intestinal perforations or obstructions. Be careful giving excessively fatty foods to your pet. These can cause severe vomiting and diarrhea.