Dec 05 2012

Feline Hyperthyroidism


Beazle, a 12 year old, neutered male, DSH, came to see us on Wednesday July 22nd, 2009, for his annual check up and vaccinations. Beazle was looking a bit “scruffy” and when we set him on the scale we discover that he had lost about a kilogram since his last visit a year earlier. We discovered several more things about Beazle when speaking with his owners. He had been drinking and urinating more than usual and had been vomiting, as well – about once a week. His owner says that he is sure Beazle is in perfect health; his cat has never had more energy!


Beazles physical exam was unremarkable. So far he seemed like a pretty healthy cat. However, knowing that Beazle had been drinking and urinating more than usual made us suspicious. Increased thirst and urination is a common sign for many serious disease processes, such as, diabetes, hyperthyroidism and kidney disease. Because of this and because Beazle was now a senior pet, we decided to run a geriatric blood panel.

The results from the lab were in the next morning and they showed that Beazle had an elevated T4 (thyroxine level). The good news was that there were no other abnormalities on the results – it seemed we had found it before any other body systems could be damaged. When left undiagnosed and untreated for too long, hyperthyroidism can cause kidney and/or heart failure; both are fatal.


Beazles owner was given three options:

1) Medication – medication will not cure hyperthyroidism but it can control it

2) Surgery – surgery is highly effective in curing hyperthyroidism but is rarely recommended due to the anesthetic and surgical complications. Over 70% of the cats with hyperthyroidism have bilateral thyroid involvement which makes surgery much more risky.

3) Radioactive iodine therapy – this is considered the gold standard of hyperthyroidism treatment in cats. It is successful in over 80% of patients and involves a single nonstressful procedure.

Beazles owners decided to try medication but after a few months, they have now decided to have the iodine therapy preformed.

We will update this page after his treatment is complete.

What is it?

Hyperthyroidism is a common disease that occurs in older cats as a result of excessive production of thyroid hormone. A benign growth or adenoma of the thyroid gland in the neck is responsible in most cases for excessive production of the hormone. This speeds up the body’s metabolism and affected cats tend to lose weight despite ravenous appetites. Other signs can include excessive thirst and urination, frequent vomiting, diarrhea or constipation, a “scruffy” looking coat, elevated heart rate, hyper-excitability and nervousness. When left untreated it may cause cats to suffer from inadequate kidney function and heart disease.

Luckily, there are options.

Medication is a common choice among our clients; however, there are quite a few disadvantages. Your feline friend must take a pill twice daily (365 days a year) to keep the hyperthyroidism controlled. There have been cases where, after long term use of medication, the thyroid glands become refractory (unresponsive) and there may be side effects, such as, vomiting, anorexia, fever anemia or lethargy. T4 levels must be monitored closely; as the medication can make their thyroid levels too low (this has its own serious issues). Your cat will need to have blood work done every month until the dose is perfected and then every three to six months after that depending on how well he/she does.

Surgery used to be a common option but with advances in veterinary medicine, it is rarely offered anymore. Once the thyroid gland is removed, the cat will no longer be able to produce thyroid hormones: thus, eliminating the problem. As you can see on the picture above, the thyroid glands are located in a very risky area. Besides the trachea and esophagus, there are also jugular veins and carotid arteries to watch out for. Usually the cats we see are very ill and are not candidates for anesthesia anyway.

Radioactive Iodine Therapy is the “gold standard” for treating hyperthyroidism. 131I therapy has an estimated 80% – 100% success rate. Your cat will need to be hospitalized at a specialty centre for about a week (7 days). While there, they receive one (usually painless) injection which destroys the thyroid tissue (leaving the rest of the cat unaffected). For the rest of your cats stay, his/her body will be eliminating all or most of the radioactivity (mostly through urine). Because only the thyroid gland utilizes iodine, other parts of the body are not damaged.

Cats with hyperthyroidism can go on to live many years past the time of diagnosis. We are more than happy to answer any questions you may have about any of the treatment options and help you decide what is best for you, your family and your pet.

Lifelearn Admin | Uncategorized

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