Hyperthyroidism AND IBD

by Pat
(New York, NY)

My cat Pippin, 17 years old, was vomiting, lost weight and acting irritable. I assumed she had cat thyroid issues, since her sister was treated for feline hyperthyroidism when they were ten. When I took Pippin to the veterinarian, my vet said he felt a thickening of my kitty's small intestine and that she probably had IBD. Her blood tests also showed a high T4, confirming that she did have feline hyperthyroidism.

I started giving her the feline medication Methimazole to treat my cat, but she began projectile vomiting. So I stopped the cat medication and took her back to the vet. He gave her Prednisone for her feline IBD. That has worked well, and my cat has since stopped vomiting and is gaining some weight.

My question is that, now that she has stopped vomiting, I would like to treat her feline hyperthyroidism. Is it okay for me to give her both Prednisone and Methimazole? Or is surgery or radioactive iodine treatment preferred for treating a hyperthyroid cat with IBD?

Dear Pat,

All feline hyperthyroidism treatment should begin with a cat medication like Methimazole. This is because, especially considering your cat's age, you first need to establish how your cat's kidneys will respond to the treatment of her feline hyperthyroidism.

There is a close, see-saw-type relationship between thyroid levels and cat kidney function levels. As the T4 level in a cat increases, the Creatinine level (a measure of kidney function in cats) is driven downward. In the case of creatinine, the lower the number, the better the kidneys are functioning. However, because of the see-saw effect between hyperthyroidism and kidney function, your cat's kidneys may appear healthy while her thyroid levels are high when they are actually showing some signs of insufficiency. Feline hyperthyroidism can create a false sense of cat kidney health.

Ultimately, the goal is to achieve a happy medium, where both the kidneys and thyroid are functioning within normal limits. By treating your cat's hyperthyroidism with an oral cat medication, you can begin to gradually decrease her thyroid levels and see how her kidney levels respond. Especially with a 17-year-old cat, there is a chance that, by getting her thyroid under control, her kidneys values may become too elevated. With an oral feline medication, you can easily increase or decrease the dose depending on how both her thyroid and kidney values are responding to her treatment.

Why is this important? Because feline hyperthyroidism treatments such as surgery and radioactive iodine will completely remove the thyroid levels from your cat's system. This can put her kidneys at risk. If your cat's T4 dropped so suddenly and her hyperthyroidism had been keeping her kidney's functioning well, she could go into acute kidney failure.

Fortunately, there is no problem in giving both prednisone and methimazole to a cat at the same time. Of course, regular bloodwork will be needed to check your cat's T4 and Creatinine levels, and her feline IBD symptoms should be monitored by your veterinarian as well. But, all things considered, I would definitely recommend that you discuss re-starting the methimazole to treat your cat's hyperthyroidism with your vet.

Best wishes,
Dr. Neely

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