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Hyperthyroidism in Cats

Updated on April 24, 2009

Like Chronic Renal Failure, Hyperthyroidism is, unfortunately, a common occurrence in cats. If you know any people who have this condition, you know may already know the basics of what this diagnosis means: Your cat's hyperthyroid gland is working overtime, producing too much of a good thing, which will eventually lead to very bad things if not reversed in time. My 13 year old cat was diagnosed with Hyperthyroidism, but her case was not entirely textbook, as she already had diagnosis of CRF. The following is what happened with her, and may vary a bit from that which other cats experience.

Feline Hyperthyroidism Symptoms

These symptoms can vary tremendously, given that the thyroid gland can affect so many aspects of a cat's health. This list is what stood out most for my cat, but I've also included symptoms she didn't have, but which other cats often experience.

Patchy Hair Loss : This was the first major symptom I noticed. There are no images on the internet of what I saw, and I wish I'd taken photos so that others could see. The patches, in my cat's particular case, were in the neck area, at the back. It looked EXACTLY like ringworm and the vet thought that was what it was. I was quite sure it wasn't, and when the test results came back we saw that I was right.

General hair looseness : If you grabbed a bit of hair from anywhere on her body and gave it a gentle tug, 7 or 8 pieces of hair would come out very easily. These bits of hair, when examined closely, were in the telogen phase. The hair wasn't breaking off, nor was it really falling out.

Poor Coat Quality : My cat was black and had beautiful shiny fur until right about the time I noticed the other symptoms. She developed really tremendous dandruff and her coat was starting to look greasy.

Vomiting : She'd vomited off and on before her CRF was manageable. When the Hyperthyroid problem started, that vomiting came back.

Increased Appetite : During the week that I noticed these symptoms, she was eating more and being very vocal about wanting more food. My cat was quite a piggie when she was younger so I didin't think this was too strange, but in conjunction with the other symptoms it was something worth noticing.

More symptoms

Agitation : If your cat suddenly seems annoyed or agitated on a consistent basis, this may be a symptom of hyperthyroidism.

Increased Appetite/Weight Loss : This is a very common pairing with many cats. People describe a voracious appetite with inexplicable weight loss. If you see this, go to the vet immediately.

Decreased Apetite : Some cats will actually go the opposite direction and eat less, as opposed to eating more.

Heart problems  :  Untreated hyperthyroidism can result in heart failure. Fortunately, this is often a reversible condition if caught early.

Retinal bleeding  :  If you see blood in your cat's eye, this could be a sign of a retinal bleed, which could be a symptom of hyperthyroidism/increased blood pressure.

Racing heartbeat  :  Cat's have very fast heart beats normally, but a super tachy cat (usually faster than 200 bpm) could indicate hyperthyroidism.

Goitre :  If you can see or palpate a goitre, this is a good indication that a cat has hyperthyroidism.

Diagnosis and Treatment

A blood test is necessary to determine for sure whether or not a cat's thyroid is producing more hormone than it should. Once that's determined, treatment is generally quite simple and straightforward -- your vet will prescribe a hyperthyroid medication that will suppress the production of the thyroid gland until the levels are healthy.

Anti-Thyroid Tablets : My cat took half a tablet twice daily (I'd mention the name but it's not available in the US and I don't want to confuse anyone) and it worked very, very well. Her vomited stopped immediately.

Other medications : There are said to be some holisitic medications, and they may work, but I suggest discussing them with your vet first.

Surgery : If you choose to have surgery to remove your cat's thyroid tumor, be very sure your vet has a lot of experience with this -- it's not an easy procedure in cats and many of them will not want to try it as a first course of action.

Radioactive Iodine : This is not available everywhere, and it's quite expensive, but if you can afford it, this may be the best option for your cat. I encourage a lot of research before you make that decision though.

Appetite stimulators: These medications can sometimes suppress the appetite. This is serious, because your cat needs to be eating to maintain their health. If your cat stops eating, talk to your vet about this and you can determine what method to best encourage him to eat.


  • Anti-thyroid medication is forever. It's not a cure; if you give these to your cat, you will need to do it for life. The day you stop medicating is the day the illness returns in full-force. If your cat is young at the time of diagnosis, treatments which seem expensive may actually be more cost-effective in the long run -- provided, of course, the odds of survival are not worse than traditional anti-thyroid medication.

  • My cat's hair was gorgeous again within 72 hours of starting the tablets. Literally, I'm not exaggerating. Her hair grew back within 3 weeks and she looked beautiful. If the only major issue the thyroid, and if the cat tolerates medication well, you have very good odds of seeing your cat return to very good health almost immediately.

  • Her personality returned to normal and she was once again happy and purring. She tolerated the tablets well and didn't suffer from any side-effects. Unfortunately, she died from CRF complications a few months later, but I've no doubt that she'd have lived a normal long life on this medication if she hadn't had a pre-existing, and fatal, condition.


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