Originally Posted by kittymonsters
KT Lynn, please tell me you have your kitty on thyroid replacement hormone. I-131 destroys the thyroid so they then become hypothryroid and must have hormone replacement. they should also have her T4 status monitored periodically.
I agree that 1-131 is the best treatment. One of my kitty's had a toxic reaction to the tapazole and it was damaging her liver, thus not a long term option for her.
Vets generally want to do a month or so on tapazole before irradiation because hyperthyroidism can cause kidney damage. This is because it increases blood pressure which hyperperfuses the kidneys and damages them. When the thyroid hormone levels are brought back down to normal the blood pressure also decreases, then the kidney damage shows up.
If your kitty is caught early the likelihood of kidney damage so soon is minimal. Long term prognosis is good. This is one of the common kitty diseases that are readily treatable.
Where are you getting your information about thyroid replacement hormones? The majority of hyperthyroid cats treated with I-131 do not
need supplementation with thyroid hormones. Radioiodine targets the hyperactive thyroid cells, destroying them. The normal thyroid cells (which are not destroyed in most cases) usually begin to function on their own in 1-3 months, though in some cases it takes 6 months, and occasionally supplementation is needed if the cat's normal thyroid cells don't kick in.This study
indicates that depending on where the tumor is located, 60-83% of cats were not hypothyroid. In this larger study
[note: this is a Word document], however, only 2.1% of cats actually needed supplementation with thyroid hormones--not all hypothyroid cats required supplementation since asymptomatic hypothyroidism is not dangerous like hyperthyroidism. Please note the following statement from this study: "In addition, because hypothyroidism may be transient, thyroxine treatment should be withheld until clinical signs of hypothyroidism develop."
For Mutty's human, definitely proceed with the additional testing, but please consider early treatment. Treatment with radioiodine is most effective when done early, before the thyroid tumor has grown substantially and before the excess thyroid hormone has had time to damage the heart, liver, and kidneys. I wish I had had the procedure performed on Spot when I first found him rather than waiting 9 months. Spot had been hyperthyroid a long time by then (he was already hyperthyroid and thin when I found him), and his thyroid resisted the treatment. By the time we tried the second treatment, his heart condition (which was probably not caused by the hyperthyroidism but may have been made worse by it) had worsened and I lost him. Early treatment is the best bet in giving you many more happy healthy years with your cat. While it is expensive up front, the long-term testing and medication is even more so.