P1/Not really sure what I'm asking, maybe looking for some reassurance? My cat is hyperthyroid and was on methimazole for a while, we kept needing to adjust the dose. He is otherwise happy and living life well, so I decided to go for radioactive iodine treatment. He just had his 1 month posttreatment checkup and his thyroid levels are higher than ever. We are in contact with his vet and the treatment center, and he is going in for another scan at the treatment center as soon as possible. He's lo
P2/ lost a pound and a half since treating with radioactive iodine and I just feel awful. I weighed the pros and cons and thought I had made the right decision to help him. This isn't an emergency, we have a plan in place, I just wondered if any of you have experience with hyperthyroid in cats? Any thoughts? I hate to think that he is uncomfortable. All his other labs are normal, it appears to just be his thyroid.
Hyperthyroidism is super common and usually fairly predictable with most cats responding as expected to medication or to radioactive iodine, but I’ve seen a few curve balls.
I recall one patient who ended up on 15mg carbimazole three times a day (so 45mg per 24 hours) and was still not controlled (the average dose for a cat is 5mg twice a day, so 10mg total in 24 hours). Our working theory for him was that he actually had a malignant thyroid cancer pumping out the thyroid hormone.
Now, I would have loved to have sent that patient for radioactive iodine or imaging as there was definitely something amiss there, and it wasn’t the cat spitting out tablets as it was worse on methimazole transdermal gel.
It’s entirely possible for malignant thyroid cancers to look like ordinary hyperthyroidism. Sometimes you can feel them in the neck or feel a cyst, and some of these are treated by (very tricky!) thyroid removal and hoping you don’t remove the parathyroid glands as well. Some are treated with more radioactive iodine.
Sometimes they throw another curveball because while the thyroid is usually in the throat, you can have extra thyroid tissue inside the thorax where you can neither see nor palpate it. this may require some fancy imaging to detect.
If radioactive iodine didn’t reduce his levels, if those levels keep growing, there is something odd going on and that next scan might be enlightening.