Monday Medical: Feline Hyperthyroidism

If you've seen Sunday's post then you already know that January is National Thyroid Awareness Month. As we mentioned yesterday, while we're sure its inception was aimed at raising awareness of human thyroid disease, that same disease is often found in our pets as well.

Hyperthyroidism usually occurs
in cats over 10 years of age

In fact, hyperthyroidism (an overactive thyroid gland) is the most common glandular disease in cats.

And it's a "mature cat" disorder - less than 6% of cats diagnosed with hyperthyroidism are under the age of 10. If not treated, it can cause heart disease and be deadly. If the hyperthyroidism is treated, the heart disease is often reversible.

Interestingly, the symptoms for hyperthyroidism are the same in kitties as they are in humans. They're all associated with an increased metabolic rate. Take a look:

Symptoms:

• often the most noticed sign is that of weight loss despite a healthy or increased appetite
• hyperactivity (your sedate, mature cat suddenly goes crazypants and starts acting like a kitten again!)
• increased shedding (I know what you're thinking, and yes, it's the same with people, too)
• panting (probably due to a slightly increased heart rate and the feeling of being overheated)
• looking less groomed than usual
• increased thirst (which invariably leads to increased urination...)
• and about half of cat owners report seeing their cat vomit, possibly due to upset stomach

What's causing all this nervous activity?  Excessive amounts of a thyroid hormone called thyroxine, or T4, circulating through kitty's bloodstream. Most often, a simple blood test can confirm these elevated T4 levels. About 10% of cats with hyperthyroidism won't show elevated levels - usually due to other medical complications. (In such cases, there are other tests that can be done, including one called Free T-4.)

The good news is that hyperthyroidism in cats is almost always caused by a benign tumor called an adenoma - and there are effective treatments to stop it. 

Option #1: Medication to suppress/regulate the thyroid gland. There is one drawback: your cat must be on the drug - daily - for the rest of his life. Additionally, periodic tests will need to be run to ensure proper dosage.

Option #2: Surgery to remove the thyroid gland (and the benign tumor). Before you wince at the thought of any vet bills that may accompany a surgical procedure, consider this: the cost of a one-time surgery may actually be less than daily medication - and the associated cost of periodic blood tests - for the rest of your cat's life.

Option #2 may not be a viable option to all older cats, however. There may be other health issues that would make surgery a bit too risky for your vet to recommend. In this case, there's a third option.

Option #3: Radiotherapy with Iodine-131.

This is a radioisotope of iodine and has a half-life of only 8 days. It's been used to treat hyperthyroidism and thyroid cancer in humans since 1941, and is still in use today.

Iodine-131 is injected directly into your cat's thyroid - and that single injection is like a precision strike to the adenoma. Target: eliminated.

The only thing left to do is to wait out the I-131 as it decays and is eliminated from the body. During that time, your cat will need to be kenneled at the clinic that administered the treatment until the I-131 has decayed to a low enough level that he can come back home.

The cost for Option #3 is comparable in most instances to the cost of surgery, without the risk posed by surgery or anesthesia.

"I resemble that remark..."

This would be our personal therapy of choice - and it's the option that Dr. Lisa Pierson of catinfo.org recommends as the best choice. But we also understand we're probably a bit more comfortable with radioisotopes than most people, simply because Marty is a Nuclear/Radiation Physicist and deals with radioactive materials and their safe handling on a daily basis.

We're happy to know there are reliable diagnoses and three treatment options to choose from. And we'll be sure to order diagnostic testing should any of our kitties ever suddenly go suspiciously crazypants in their golden years.

 (Faraday excepted, of course. We don't think he'll *ever* be normal...!).



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Sources:
The Cat Thyroid Center 
Radiocat.com
Little, Susan (2006). "Feline Hyperthyroidism" (PDF). Winn Feline Foundation. Retrieved 24 June 2009.
Dr. Arnold Plotnik's article on Feline Hyperthyroidism for Petfinder
WebMD's article on hyperthyroidism in humans
Insights into Veterinarian Endocrinology - Mark Peterson, DVM: Hyperthyroidism in dogs
News Medical: history of I-131 use