Hyperthyroidism – Part Deux

Jennifer Coates, DVM
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Published: November 3, 2011
Hyperthyroidism – Part Deux

I am now the proud "pet parent" to two hyperthyroid kitties, and since we only have two cats, we have a 100 percent attack rate at our house. I guess I shouldn’t be too surprised, since I’ve been running a home for geriatric animals for the past decade or so, but geeze, I wish someone could figure out the cause of this all-too-common affliction of older cats.

To recap, last year I diagnosed Victoria, my 12-year-old calico, with hyperthyroidism. After stabilizing her condition with the oral drug methimazole, checking kidney function, etc., etc., she underwent (radioactive iodine) treatment and has done fabulously ever since. The most interesting thing I learned from her case was that even though treating her with methimazole brought her lab values back to normal, her physical condition never really changed that much… she still looked "hyperthyroid." That is, skinny, scruffy, hungry, and manic. All that changed within just a week or two of her treatment; making me wonder what we’re missing with the cats that remain on methimazole long term.

This time around is going to be a different story, however. Keelor is 17 going on 18 and has chronic kidney disease to boot. He is not yet azotemic (i.e., there is no evidence of kidney failure on his blood work), but he cannot concentrate his urine and his kidneys feel about 2/3 of their normal size. This makes him a poor candidate for treatment because lowering his thyroid hormone levels too much could worsen his kidney function, and therapy is not reversible.

I started Keelor on a low dose of methimazole and will be rechecking his thyroid level and kidney values in a couple of weeks. The goal is to find a dose of methimazole that won’t appreciably decrease his kidney function but will still improve his hyperthyroidism — a real balancing act.

I’ll need all the luck I can get, because to make the situation even more interesting, Keelor HATES blood draws. He is a gentle, mild mannered fellow until he is restrained. Even then, he doesn’t really fight, he just waits and watches until the needle gets close and then it’s a head bob to the right or a wiggle to the left, just enough movement to prevent you from hitting his vein. I had to sedate him for this last blood draw, and I’m not willing to do that over and over again as I’m afraid the risks to his kidneys might soon outweigh any benefits.

I do have another option for treatment. A restricted iodine food just became available for hyperthyroid kitties. It might be a good choice in some situations, but I like to let a new product be "battle tested" for a while before using it on my patients. I think I’ll hold it in reserve and reconsider if Keelor reacts poorly to the methimazole.

Sigh … Keelor is the first cat I ever "owned." I call him my primary kitty. Unfortunately, the combination of chronic kidney disease and hyperthyroidism is a tough one to manage, and I have a bad feeling that I’ll have to say goodbye to him in the not too distant future.

We’ve had a good run though, old man; I plan to spoil you rotten from here on out.

Dr. Jennifer Coates

Image: Lilly by Karen Flower / via Flickr

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