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Hyperthyroidism in cats is a common metabolic problem in senior cats, and it is often hard to make a decision as to how to treat this condition given the age of cats at diagnosis. We review the three most common treatment options, medication, surgery and radioactive iodine therapy for cats. Managing hyperthyroidism correctly can make a world of difference to your senior cat’s quality of life.
Understanding Hyperthyroidism in Cats
Hyperthyroidism in cats arises from overactivity of the thyroid gland. This is usually due to non-cancerous ‘growth’ of the gland. We don’t yet know what triggers this growth to occur. The thyroid gland is responsible for controlling metabolism, therefore excessive activity of this gland causes symptoms associated with an increased metabolic rate. You may have heard people talk about weight gain and lethargy due to an underactive thyroid, it is the opposite for hyperthyroidism.
The most common signs observed in cats with hyperthyroidism include:
- weight loss despite a good or ravenous appetite
- hyperactivity displayed as restlessness
- vocalisation or aggression
- increased thirst and therefore increased urination
- unkempt coat due to poor grooming
Diagnosing Hyperthyroidism in Cats
At this point you may be thinking, “that sounds similar to signs of kidney disease or diabetes” and you would be correct. It is virtually impossible to differentiate hyperthyroidism from chronic kidney disease (which also commonly occurs in older cats) based on clinical signs alone.
Diabetes however, usually occurs in younger animals and many diabetic cats are weak rather than restless. Hyperthyroidism in cats is diagnosed by blood and urine tests (which will also differentiate between hyperthyroidism, chronic kidney disease and diabetes) after a careful clinical exam by your veterinarian. The blood test will detect elevated levels of thyroid hormone in the blood in the case of hyperthyroidism, although levels may be normal in very early cases or if there is another serious illness.
Why it is Important to Treat Hyperthyroid Cats
Although the clinical signs of hyperthyroidism in cats don’t sound that bad, hyperthyroid cats should be treated since it is the signs you don’t see that are affecting your cat’s quality of life. That overactive metabolism is causing all sorts of havoc internally:
- the heart is racing and therefore has to work harder, leading to heart enlargement
- blood pressure may be elevated to dangerous levels causing retinal detachment and subsequent blindness
- the body is burning up energy, which is worsened by having to produce more red blood cells to carry more oxygen to ‘overactive’ tissues
- there may be osteoporosis leading to weak bones.
With your cat’s body running in overdrive, eventually their energy reserves are used up (hence the weight loss) and there is no energy to put into bodily functions like maintenance of the immune system, thereby increasing susceptibility to infections. Many older cats may already have bad dental disease, increasing this risk.
Although I would never put a cat to sleep based on a diagnosis of hyperthyroidism if the owners refused to treat, I do think treatment is warranted to maintain quality of life.
Treatment of Hyperthyroidism
There are three categories of treatment for hyperthyroidism in cats:
- medical treatment
- or radioactive iodine therapy.
Medical treatment of feline hyperthyroidism only manages the disease while surgery and radioactive iodine therapy can cure the disease.
The major caveat for treatment is whether or not there is concurrent chronic kidney disease – one of the benefits of hyperthyroidism is that it improves blood circulation through the kidneys which may compensate for diseased kidneys. Therefore treating the thyroid disease may lead to overt kidney failure or significant worsening of pre-existing kidney disease. It is a delicate balance in cats that have both conditions to balance the thyroid treatment with the kidney disease to minimise the adverse effects of both, and in many cases it may not be worth treating the thyroid disease in this situation.
I always recommend treating newly diagnosed hyperthyroid cats medically for one or two months and closely monitoring kidney function, and only if the kidneys are stable after this time would I proceed to surgery or radioactive iodine therapy.
Medical Treatment for Hyperthyroid Cats
Anti-thyroid medications are most frequently given as tablets and this can be very challenging in some cats, especially as they may require tablets multiple times a day for the rest of their lives. Side effects are uncommon but include vomiting, inappetence and lethargy. More serious side effects are rare.
An alternative option is a cream that is applied to the inside of the ear and the medication is absorbed through the skin. This is much easier to give and has fewer side effects but is unfortunately is also more expensive. Note: you should wear gloves when applying this medicinal cream to your cat, since it is designed to be absorbed through the skin!
In the first few months of treatment, it is important that a vet closely observes your cat by watching clinical signs and conducting blood and urine tests to monitor the levels of thyroid hormone and to check the kidney status. As a result of this monitoring, the first few months of treatment can be expensive. However, once stable, blood tests can often be done once or twice a year to check that your cat’s thyroid hormone levels remain normal.
Surgery can cure hyperthyroidism in cats, but is a technically challenging procedure and you will likely be referred to a specialist surgeon. Therefore surgery is an expensive option – however it only needs to be done once. As with all surgical procedures, there are a number of risks associated with surgery and anaesthetic (remember heart disease is common with hyperthyroidism). You should discuss the risks in detail with your veterinary surgeon before the procedure.
Radioactive Iodine Therapy for Cats
In my opinion, this is the best treatment option for hyperthyroid cats, particularly if diagnosed ‘young’ (e.g. 10-12 years old) since the alternative is daily medication for life. Radioactive iodine therapy will usually require referral to a specialist as most veterinary clinics don’t have the facilities to perform this procedure. The medication is given as a tablet and specifically targets the overactive thyroid tissue and destroys it. The radioactive iodine therapy procedure is very safe and effective but usually requires a stay in hospital of a week or so. Like surgery, this procedure is expensive but is only done once, so the overall cost needs to be compared against the cost of ongoing medication and monitoring including blood tests.
> Learn more about the risks associated with radioactive iodine therapy for cats with hyperthyroidism.
Prognosis for Cats with Hyperthyroidism
Prognosis for both management and cure of hyperthyroidism in cats is EXCELLENT as long as there is no concurrent kidney disease. Symptoms are reduced very rapidly and the body starts to return to normal, including the heart in early cases.
I firmly believe treatment of hyperthyroidism makes a huge difference for our senior cats, and for owners too by reducing the vomiting, diarrhoea, yowling, aggression and sometimes inappropriate urination that are symptoms of this disease.
Although older cats can live with hyperthyroidism, treatment significantly improves their quality of life. It’s often hard for a vet to explain all of this in a short 15 minute consultation so hopefully this answers some of the questions you might have if you are living with a cat with hyperthyroidism.
Marcy Matasick says
My cat is living proof that hyperthyroidism can be successfully treated with a low-iodine diet. My cat was diagnosed with hyperthyroidism at age 13, after a year and a half of eating a cat food that was “guaranteed” to cause weight loss. Yes, he had lost weight on that stuff, but he’d become very ill, too: he was vomiting several times a day, anxious and yowling all the time, drinking and peeing great volumes of water, was too weak to jump up on a sofa, he even got aggressive with me. The vet also said his heart rate was dangerously fast, and he was dehydrated despite all the water he drank. I learned later that the weight-loss cat food he’d been eating contained excessive iodine, which likely over-stimulated his thyroid gland and caused thyroid tumors. When the vet told me the treatment options I balked: either surgically remove his thyroid gland and give him thyroid hormone supplements the rest of his life, or give him anti-thyroid medication the rest of his life. Either would require many expensive vet visits to adjust his thyroid hormone levels until he was stable. I said no to both. I decided instead to restrict the iodine in his diet. As soon as I changed his diet he stopped vomiting, and over the next several months all his other symptoms cleared up. The iodine-restricted diet meant no fish or seafood, no salted human foods because table salt is usually iodized, and no cat food containing iodine supplements in the form of potassium iodide, calcium iodate, or kelp. I read all the cat food labels and at first I could not find ANY cat food that didn’t contain either fish or iodine supplements, or both. So I fed him raw poultry and unsalted bone broth. (My reasoning was that cats evolved eating whole animals including bones, and raw meat was only muscle, so I assumed bone broth should contain some of the nutrients in bones that he needs.) Eventually I found Hill’s prescription low-iodine YD food, and this is mainly what he’s been eating for almost 2 years. I also give him raw ground chicken sometimes, and unsalted bone broth because he loves it. He’s now 15 — and in perfect health! He recently had blood work done and all his blood levels are normal, including his thyroid hormone level. The vet said she’d never heard of treating hyperthyroidism with diet alone, but said I should keep doing what I’m doing because it’s clearly working.
Please consider that the cause of so much hyperthyroidism in cats may be the iodine supplements in cat foods. And please recommend that your clients try a low-iodine diet before more drastic treatments.
Thank you so much for your info. I just a bought a bunch of new cat food with no fillers or iodine and will feed mainly meat and poultry from now on.
My 14 year old cat has recently been diagnosed with hyperthyroidism and we’ve started medication. Sometimes I’m out of the house for a long time…does it matter if I’m late with a dose or miss one?
Dr Robyn says
It’s probably best to confirm with your vet in case your cat has other conditions that influence the hyperthyroidism but as a general statement in my opinion, the occasional skipped or late dose is not a big deal. The effects of hyperthyroidism occur due to persistently elevated levels of thyroid hormone. If levels creep up for for a few or 12 or even 24 hours it is not going to cause all the chronic changes we talked about. Hope your kitty is feeling better on his/her medications 🙂
This is a really informative post! I’m curious whether certain breeds of cat are more likely to develop hyperthyroidism than other breeds and at what age the disease most commonly develops?
Dr Robyn says
There is no strong evidence showing that any particular cat breeds are predisposed to hyperthyroidism. One study stated that non-pure bred cats were at a higher risk of developing hyperthyroidism but another study said domestic shorthairs were less likely to develop the disease. So I don’t believe there is a strong genetic predisposition.
Hyperthyroidism is a disease of older cats. The average age at diagnosis is 13 years old, but cases have been reported over a wide age range e.g. 4-22 years old. Only about 5% of cats diagnosed with hyperthyroidism are less than 10 years old.
My cat is 17 and was diagnosed with hyperthyroidism almost 2 years ago. We started using the tablets and then switched to the cream applied to the inside of the ear, alternating left and right ear morning and night as advised by our vet. He has lost some weight, but he’s doing ok. Thanks for the informative article it has helped me understand his condition a bit better.
Sharon S. says
Thank you for providing this important information. I had no idea of all the complications hyperthyroidism can cause in a cat’s body.