Hyperthyroidism is one of the most common diseases in middle aged and older cats. The usual cause is a benign tumor of the thyroid gland that results in too much thyroid hormone being produced.
Thyroid hormone helps regulate metabolic rate so the symptoms of hyperthyroidism are due to an abnormally high metabolic rate. Affected cats usually eat more and lose weight. They may have faster than normal heart rates, vomiting and diarrhea. Long term effects can include blindness, heart disease and kidney problems.
There are three primary treatment options all of which have certain risks and rewards. For years veterinarians have used a human drug called
methimazole. This is called an off label use since the drug is not approved for cats. Off label use is not at all uncommon in veterinary medicine. One of the drawbacks with this drug is that it only comes in 5 and 10 mg tablets. The usual dose for a cat is 2.5 mg so owners are forced to break the tablets in two.
This can be a problem because it's not always possible to do that evenly and you expose the bitter inside of the tablet. Cats can be tough to pill on good day so giving them something bitter only makes it worse.
Now we have our own form of methimazole called Felimazole. The advantage is that it comes in coated 2.5 mg tablets and it's been tested in clinical trials with cats and it's effective.
Pills can have side effects and Felimazole is not a cure, but it is a good initial treatment option and it can be used long term in cats with kidney disease.
Radioactive iodine is another treatment option. This is a very effective way to control an over active
thyroid gland but it is not without risk, either. You may have to go to a special facility that handles this potentially toxic stuff and your cat may have to stay there for up to ten days until he's not radioactive anymore. You may also end up with a
hypothyroid cat, too.
Surgery is the other option but it can be risky in some older cats especially those with kidney failure and heart disease. Surgery can result in hypothyroidism, too. There are a couple of tiny glands called the parathyroid glands that may be damaged or removed during thyroidectomy if the surgeon is not careful. You need these little glands to regulate calcium and phosphorus levels. That's an important function.
If your cat is diagnosed with hyperthyroidism be sure to discuss all the options with your veterinarian. The choice of treatment will depend on your cat's overall health. It is nice to have our own FDA approved drug in our bag of tricks though.