Cats w/ Hyperthyroidism & I-131 Therapy (Need advice)

j_eden

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Hey guys,

Posted here a few days ago and our vet visit revealed that our guy Xiao Hua (little mix in Chinese) has hyperthyroidism. The vet has him on Methimazole for a month to see how he responds, and if all goes according to plan the vet suggested the radioactive iodine therapy for him.

It sounds scary to me, especially since your cat comes home still being radioactive. We also have two cats, so I'm just worried about how all that will work out. I've done a bunch of research on this procedure but I'd really love to hear first hand experiences. Did you have your cat go through with I-131 and what did you guys think of the experience? 

Thanks.
 

Geoffrey

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I am a human Physician in internal medicine, not a Veterinarian and any comments that I make about cats should be checked by a vet.  However I have considerable experience of using Radio-active Iodine for hyperthyroidism in humans.   

As I see it, just as there are three treatment options in humans, there are also three treatment options in feline medicine, but your vet can advise you of any others.   

1. Your cat can take Methimazole indefinitely, probably for the rest of the cat's life, the thyroid function tests will be monitored by your vet and the dosage of Methimazole adjusted accordingly. 

However, according to a study by Mark Peterson et alii in the Journal of Veterinary Internal Medicine 1988; 2:150-157,181 cats were given Methidazole preoperatively before thyroidectomy.  81 cats with hyperthyroidism were given long term Methimazole; 48, had significant side effects including loss of appetite, irritation of the face and neck causing scratching of these areas, and 10 of the 362 had severe and potentially life-threatening side effects including jaundice due to liver problems and the dangerous  agranulocytosis (or destruction of the bone marrow).  Incidentally agranulocytosis is a side effect of the same treatment in human medicine.

2..Surgery, removing the thyroid gland, a procedure known as thyroidectomy.  This may well be curative although there is a risk that your cat will have myxoedema, or underactive thyroid function.  This can be easily treated by giving thyroid extract in tablet form, however lifelong treatment will be necessary.

3. Radio-active iodine with I-131:I would not worry about the radioactivity, your vet will know the dangers of this and will keep the cat until it is safe.  From my experience in humans, this is a day only procedure and discharge the same day causes no problems. 

Your vet will monitor the thyroid function tests following the radio-active Iodine, the cat should not be aware of any problems.  In humans, and probably in feline medicine -  discuss this with your vet - there is a strong likelihood that the patient will be rendered hypothyroid  ie. will have underactive thyroid function (or myxoedema) in time and will have to take life-long thyroid extract tablets.

Whatever treatment you take, there is a likelihood that you will have to give your cat lifelong treatment.  But, if it were my cat, long term Methimazole is out because of the risk of side effects and surgery would be out because of the pain and stress that the surgery would cause the cat. 

That leaves radio-active iodine and this option is likely to have the least risk to the cat.  The most likely side effect is under-active thyroid function, requiring thyroid extract tablets - your vet will advise you of the risk of this, and how often the tablets will need to be taken. 

Radio-active Iodine therapy is therefore the treatment that I would choose.

I hope that the above will be useful to you,

With kind regards,

Geoffrey
 
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Geoffrey

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There is a typo in the above post where I wrote 362, in red  in the article by Peterson et alli:

However, according to a study by Mark Peterson et alii in the Journal of Veterinary Internal Medicine 1988; 2:150-157,181 cats were given Methidazole preoperatively before thyroidectomy.  81 cats with hyperthyroidism were given long term Methimazole; 48, had significant side effects including loss of appetite, irritation of the face and neck causing scratching of these areas, and 10 of the 362 had severe and potentially life-threatening side effects including jaundice due to liver problems and the dangerous  agranulocytosis (or destruction of the bone marrow). 

This figure in red, should of course have been 262 (cats), not 362 !  I apologise for the mistake.

Geoffrey
 
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maggiemo

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I foster a sixteen year old cat with hyperthyroidism. Her owner was unable to care for her and the cat was very thin, lost most of the fur on her rear end and tail, and permanently hungry. She has now been on Methimazole for a year and seems to be doing really well on it. Luckily it suits her. We were not given the radioactive iodine option so I can't offer advice on that. Good luck. I hope the treatments work well for you.
 

ruthm

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If you have not already done so, I highly recommend you join the Yahoo group for Feline Thyroid;there are many experienced caregivers, plus Dr. Peterson occasionally posts as well.

My girl Tiger was 16 when she was diagnosed diabetic and hyper-T. She did not tolerate Tapazole and was already too skinny and throwing up, so I was very lucky to find the Cats Exclusive clinic about 30 minutes from our home. She was there 3 days, the people there and the vet were super nice and caring. We only had to collect and hold her litter for 2-3 months and this was no problem at all. I have heard some people are afraid their cat will be too stressed but truthfully, I think it's the human that stresses over it, I have absolutely no regrets for having the I-131.  

There is always the possibility that Hyper-T is masking the early stages of CKD;so your vet will need to do bloodwork once your cat has been taking methemiazole for a few weeks.  And there is always the possibility that some kitties will end up being hypothyroid after the treatment. My girl was both of these- but she was only in the earliest stages of CKD, easily managable, and coincidentally, we both were diagnosed hypothyroid at the same time and we both took the lowest dose of Levothyroxine with absolutely no ill effects. Tiger's med was compounded into a tasty chicken flavor that she never minded taking. She lived to be close to 18 years of age before I lost her to cancer.
 
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