I can't help with your specific questions, but why can't the cat take medicine to slow down the thyroid? I was diagnosed hyperthyroid in 2002, and didn't want the radioactive cocktail, so I was put on PTU. It worked, and over time my dose was lowered until finally I don't have to take it anymore. Obviously I am not a cat, but it is worth exploring.

Here is a link that might be useful: google results - cats & PTU

I also wish I had answers for you, but don't.

My old kitty is hyper-t and takes medication. She's old and has some kidney issues, so she's not really a prime candidate for I-131. The medication for her is relatively inexpensive (the vet writes and RX and we get it at Walmart) and it's really not that bad giving it to her twice a day- we use a pill syringe, which makes it so much easier. Perhaps you could try the medication route and see how he does, and it would also buy you some time to research this and make other decisions.

Again, I don't know a tremendous amount about feline thyroids, but my cat needs a medication adjustment just about every 3 months. I don't know if that is unusual to have a thyroid that is ever changing- perhaps that sort of thing is what has happened to your cat and the I-131 that was done is just not enough to control his thyroid anymore.

I'm sorry this happened. You sound so frustrated, particularly in your other post. Hope you find some answers.

Wow, that really stinks. I totally guessed he had a different problem, but being hyperthyroid is better than my guess (which was cancer).

It's really rare for a cat to need a second I131 treatment, but then again it's really rare for such a young cat to become hyperT4. I suspect most older cats die of something else before having a chance to become hyperT4 again. I did a quick google scholar search and couldn't find anything about stats for younger cats and recurrence of hyperthyroidism. I did find a reference for an 8 month old hyperthyroid cat, and during my time as a tech for RadCats we treated an 18 month old cat. But nothing was written in the literature about long-term follow up for the young cat, except her became hypothyroid after treatment. And I don't know about the young guy we treated except he made it through fine and had a normal T4 the following year.

As far as why he's hyperT4 again, he just grew another thyroid tumor, either a benign adenoma or a malignant carcinoma. The I131 destroys all active thyroid tissue, which in theory, is all the diseased thyroid tissue (benign or malignant, doesn't matter). However it cannot destroy *future* tumors.

As far as why cats become hyperthyroid to begin with, most if the research now is focusing on environmental and food toxins. There was some research into an autoimmune problem, and some about a genetic reason, but most likely the cause is multfactorial. I went to a talk about hyperthyroidism in cats while in school, and from what I remember, she was talking about metals in fish and canning materials that suppressed thyroid tissue long-term and basically wreaked havoc on the autoregulation of thyroid hormone, eventually resulting in hyperthyroidism. The research is still on-going, and unfortunately it's hard to get grant money for it because 1) cats in general don't earn as much research money as dogs and 2) hyperthyroidism can be managed relatively easily. Here's an abstract from the AVMA journal that says cats who eat fish or giblets foods tend to be hyperT4 more than control cats:
http://avmajournals.avma.org/doi/abs/10.2460/javma.2000.217.853

Here's a review article about hyperthyroidism
http://ecommons.library.cornell.edu/bitstream/1813/11446/1/2006%20Lynn.pdf

As mentioned before, methimazole can be used to suppress thyroid hormone, as long as your cat doesn't have a reaction to the medication. It's available for oral and transdermal administration. So not being able to do a 3rd I131 treatment doesn't mean your cat can't be treated.

I couldn't find any specific studies done on the effect of radioactive I131 in cats. I know that having treated cats for many years, and being exposed to several doses every week, I never was even close to legal radiation limits. Of course I also never injected myself with it either! I linked a general article on I131 below; it has some references. You can also google beta particles and gamma rays for information on the type of radiation I131 produces. Only the beta particles stay in the cat, and they only penetrate up to 5mm tissue.

I found another abstract regarding survival times. On the good side, cats treated with I131 live longer than cats treated with methimazole. On the bad side, the younger the cat is, the more quickly it died regardless of treatment.
http://avmajournals.avma.org/doi/abs/10.2460/javma.228.4.559 Of course cats with pre-existing renal disease didn't fare too well no matter what treatment was used.

I hope Basil beats the odds and has a long happy euthyroid life after this treatment.

meghane, I really appreciate your answers! After the initial shock last week, I've made the decision to go with the second I-131 for Basil: he's admitted this coming Friday. Thank you so much for the article links: I will read them all. I guess Basil really is a rarity: I posted a message on the yahoo Feline hyper-t site and very few answered. I'm still searching for information. This is very distressing, but I'm hoping upon hope that this second round does the trick.

Just to report that Basil is home from his second round of radiation (I-131). He went in with a T value of 26, and came home two weeks later with a T value of 4. He is much more subdued--he was yowling and literally bouncing off walls when he went in. His appetite is excellent although he is still quite thin. His "job" now is to be a lazy, loved cat with lots of food. I'm so glad to have him back and I am really praying that this second round did the trick.

Marita, did they give you a price discount for the second round?

Yes, a major discount: the vet did the second round for $175. (the cost of the drug). He "guarantees" his work. The first round was about $1200. That's why I really couldn't turn the deal down.

Marita, it is great to hear an update! I would not have turned down that second round either- not at that price. I bet your guy feels a whole lot better now. You must be relieved too.