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Dr. Kara
Dr. Kara, Veterinarian
Category: Cat
Satisfied Customers: 18130
Experience:  Over 20 years of experience as a veterinarian.
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My cat (female, approx. 17-20 yrs old) recently

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My cat (female, approx. 17-20 yrs old) recently had both over-active thyroid glands in her neck removed (but the nodes to do with calcium were left). Shortly after, I noticed a lump on her lower spine on one side and one on the back of her neck. Both seem fused to her inner structure and do not move. She had an x-ray about 2 and a half weeks ago and it showed that the lump on her spine had not invaded the spinal column. The vet said she couldn't be sure what it is without taking a biopsy and if it told us it's cancer it would be too beyond reason to put an elderly cat through what would be intensive spinal surgery to remove it. Since then both lumps have practically doubled in size and she has almost completely lost her appetite, she still drinks a bit. I find the timing of finding these lumps soon after her op a little coincidental. Could they be linked? Could it be something other than cancer? Also, I have a friend who had over-active thyroids and she said when humans have them removed, they have to be put on drugs to replace a normal level of the hormones produced by thyroid glands. Is this the same with cats (she was not put on any meds after the op)? My friend thought this might have some link with her lost appetite. Also, over roughly the last week, she has increasingly lost control over her hind legs, to the point where she can't really walk as they just fold under her, she more drags them, than uses them, if at all. She has also lost a huge amount of weight since an initial increase in weight after the op.

Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your girl has been through so much recently with surgery to remove her thyroid glands and now firm, well attached masses near her spine that are growing rapidly.
I honestly do not believe that the masses are related to her surgery. I think it is an unfortunate coincidence that she developed them so soon after surgery. The location of these lumps, their firm make-up and their rapid growth make me think that she has vaccine associated fibrosarcomas. These tumors are thought to be stimulated to develop as a reaction to something in the vaccine. They are relatively uncommon (1 in 10,000 vaccines will stimulate a tumor) but they are highly aggressive, fast growing tumors. As your veterinarian told you diagnosis is achieved via a biopsy, and treatment must be extremely aggressive to have any chance of a cure. In many cases even with aggressive treatment the tumor returns. That is likely more than your girl can handle now especially with an already poor appetite.
If you'd like to read more about these tumors please look at this link:
It is true that people must go on thyroid replacement hormones after treatment for thyroid tumors. This is very, very rarely the case in cats. They seem to have other sources of thyroid hormones that take over once the tumors are removed or treated with radioactive iodine. We suspect that, unlike us, they have small clusters of thyroid tissue cells near the primary glands that act as replacement glands should anything happen to their primary thyroid glands.
Her decreased appetite may have to do with the sudden drop in hormone levels. Though they are at normal levels now her body is used to being hyperstimulated. It is also possible that she has other metabolic disease processes (like kidney disease) that were masked by her hyperthyroidism and are now becoming apparent. Hyperthyroid kitties commonly have kidney disease too that only becomes apparent when the thyroid hormone levels drop.
Her weakness in her rear legs could be due to changes in electrolyte or mineral balances due to metabolic diseases, like kidney disease, affecting her muscles or it may be due to the firm masses. Though they are not affecting her bony vertebrae in the location they are in they can still affect nerve roots leaving the spinal cord.
At this point I recommend repeat blood tests and a urinalysis as well as a T-4 to evaluate her organ function and electrolyte and mineral balances.
I would also recommend trying an appetite stimulant like mirtazapine to try to get her to eat better.
Please let me know if you have any further questions.
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Customer: replied 3 years ago.

Thank you very much for your answer, I really appreciate your advice.

You are very welcome. Please let me know how things go for your girl or if you have any follow-up questions, Dr.Kara.