Feline Hyperthyroidism and Recurrent UTIs?

by Rick Norell
(Idaho Falls, ID USA)

Our cat "Honey Girl" is about 12 yrs old (a guess since she was a rescue cat). She was diagnosed with feline hyperthyroidism three years ago. We started treatment with a liquid form of tapazole and continued for 12 months, including a dose titration early on. Honey's T3 and T4 numbers did not stabilize and she had recurrent UTIs.

Our vet recommended surgery and it was done. Honey responded well to the feline surgery and had about 15 months of excellent health and regained some of her lost weight. Unfortunately, her feline hyperthyroidism has returned (high t3/t4, rough hair coat, variable eating habit, excessive thirst, defecating outside her cat litter box, blood + mucus in stool and crying at night). Presently we are treating her twice daily with 5 mg of tapazole in a transdermal gel.

Honey has had two cat UTIs during this time. They cleared up after a 20 day treatment course with the feline antibiotic Orbax. We're a bit confused on what direction to go at this point in her cat hyperthyroidism treatment...

Honey has seemed to respond to the higher dose of tapazole gel but then again has issues with UTIs. Is there anything we can do to prevent recurring UTI? If Honey does not stabilize at this higher dose, which route would you suggest: surgery or radioactive iodide?

Our vet is an excellent feline DVM and she has performed this particular surgery. On a cost basis, surgery is the better bet since it is less than 1/2 the cost of radio iodide. However radio iodide is practically non-invasive and from what I've read, radio iodide has a slightly higher cure rate than the very successful surgical approach.

Yet, she stops eating when she is not home and I don't know how she would do in the 1 to 3 week period to clear radiation from her system... Sorry for the long post but felt you needed the detail to understand her situation.

Doc, you run an awesome site and thank you for all the great assistance you've given others!


Dear Rick,

The reason your cat gets recurrent feline urinary tract infections is because cats with feline hyperthyroidism have very dilute urine (practically the consistancy water). Normal urine has defense mechanisms that keep cat urinary tract infections away. The lack of concentration in a hyperthyroid cat does not have the normal defense mechanisms in place to prevent these feline urinary tract infections. As long as your cat is not stable with her cat hyperthyroidism treatment, these urinary tract infections would likely be an ongoing issue.

What is not clear from your letter is why your cat has become hyperthyroid again. Cats actually have two thyroid glands in the neck, and with cat hyperthyroidism, one or both may become enlarged. Was only one of your cat’s two thyroid glands removed during the initial surgery? Or were both taken out?

If only one side was removed during the initial feline surgery, it is not unusual or uncommon that the second cat thyroid gland would become enlarged. If that is the case in your situation, surgery would be a wise option in the hands of a good feline surgeon.

On the other hand, if both thyroid glands were removed, this may be due to thyroid tissue being present elsewhere in your cat’s body. If our cat is hyperthyroid from thyroid tissue somewhere else in her neck or chest, then the best feline hyperthyroidism treatment option is radioactive iodine. Cat radioactive iodine treatment will destroy the thyroid tissue wherever it is in the body, and this remaining tissue may not be readily visible during surgery.

Should you opt for the feline radioactive iodine treatment, there are appetite stimulants and other methods of feeding while your cat is hospitalized if she is a poor eater. Fortunately, while she is hospitalized, your veterinarian and the staff will be able to closely monitor and assess your cat’s needs for maintaining her appetite before she is able to return home.

Because your Honey Girl is having recurrent cat urinary tract infections, this is certainly a sign that her cat hyperthyroidism is not well maintained. Stabilizing her feline hyperthyroidism should keep the urinary tract infections away.

Considering your cat being only 12 years old, I would recommend a more permanent solution than feline medications such as tapazole or methimazole for controlling her cat hyperthyroidism. Since 12 years old is actually relatively young for a cat to be diagnosed with this feline illness, and theoretically you could have many more years with her, either surgery or radioactive iodine would be ideal options for long term feline hyperthyroidism treatment solutions.

I sincerely wish both you and Honey Girl all the best with whichever treatment option you choose.

All the best,
Dr. Neely

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