Hyperthyroidism in cats is a common metabolic problems affecting senior cats. Because it usually occurs in older cats, it can be difficult for cat owners to decide how best to treat this condition. We review the three most common treatment options – medication, surgery and radioactive iodine therapy – and explain how managing hyperthyroidism correctly can make a world of difference to your senior cat’s quality of life.
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Understanding hyperthyroidism in cats
Hyperthyroidism in cats occurs when the thyroid gland becomes overactive, usually due to a non-cancerous ‘growth’ of the gland. The cause of this growth is still unkown. Since the thyroid gland controls metabolism, excessive thyroid activity causes symptoms associated with an increased metabolic rate.
You may have heard that humans with an underactive thyroid gain weight and become lethargic – hyperthyroidism is the opposite. Cats with this condition often lose weight and seem constantly restless.
Common signs of hyperthyroidism include:
- weight loss despite a good or ravenous appetite
- restlessness or hyperactivity
- increased vocalisation or aggression
- excessive thirst and increased urination
- unkempt coat due to poor grooming
- vomiting or diarrhoea.
Diagnosing hyperthyroidism in cats
At this point you may be thinking, “that sounds similar to signs of kidney disease or diabetes” – and you’d be right. It is almost impossible to differentiate hyperthyroidism from chronic kidney disease (which also commonly occurs in older cats) based on clinical signs alone.
Hyperthyroidism in cats is diagnosed through blood and urine tests after a full clinical exam by your veterinarian. The blood test will detect elevated levels of thyroid hormone in the blood, although levels may be normal in very early cases or if there is another serious illness present. These tests also help rule out kidney disease and diabetes, which can mimic some of the same symptoms.
Why it’s important to treat hyperthyroid cats
Even thought the visible signs of hyperthyroidism in cats might not seem alarming, hyperthyroid cats should be treated since it is the signs you don’t see that affect your cat’s quality of life. That overactive metabolism is causing all sorts of havoc internally and puts multiple organs under stress:
- the heart races and has to work harder, leading to heart enlargement
- blood pressure can rise to dangerous levels, risking blindness from retinal detachment
- the body burns up energy, causing muscle wasting and weight loss
- bone strength may weaken due to osteoporosis.
With your cat’s body running in overdrive, it impacts their immune system, making them move susceptible to illness and infections. Treating hyperthyroidism in cats not only extends lifespan but dramatically improves comfort and wellbeing.
Treatment options for hyperthyroidism
There are three main treatments for hyperthyroidism in cats:
- medication
- surgery
- radioactive iodine therapy.
Medication controls thyroid hormone levels but does not cure the condition, while surgery and radioactive iodine therapy can be curative.
The main challenge in treating hyperthyroidism in cats is when there’s also chronic kidney disease. Hyperthyroidism actually improves blood flow through the kidneys, which can help them work a little better if they’re already damaged. When the thyroid problem is treated and the metabolism slows back down, that extra blood flow disappears – and the underlying kidney disease can suddenly become much more obvious or even worsen.
For cats living with both conditions, treatment has to be carefully balanced to support the kidneys while controlling the thyroid. In some cases, especially when the kidney disease is advanced, it may not be in your cat’s best interest to fully treat the thyroid disease.
I always recommend treating newly diagnosed hyperthyroid cats medically for one or two months and closely monitoring kidney function. Only if the kidneys are stable after this time would I suggest 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, loss of appetite 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.
Surgical treatment for hyperthroidism
Surgery can cure hyperthyroidism in cats, by removing the affected thryoid tissue, but it’s a technically challenging procedure and usually performed by 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). So, make sure you discuss the risks in detail with your veterinary surgeon before the procedure.
Radioactive iodine therapy for cats
This is often the best treatment option for hyperthyroid cats, especially if they’re diagnosed while still relatively young (around 10–12 years old). The main alternative – lifelong daily medication – can be challenging to manage.
Radioactive iodine therapy (I-131) usually requires referral to a specialist, as most veterinary clinics don’t have the facilities to perform it. The treatment is given as a single dose (often in tablet form) that specifically targets and destroys the overactive thyroid tissue without harming healthy areas.
This procedure is very safe and highly effective, though it typically involves a short hospital stay of about a week for monitoring. Like surgery, it can be expensive upfront, but since it’s a one-time treatment, the total cost is often comparable to – or even less than – the ongoing expense of medication and regular blood tests over a cat’s lifetime.
Learn more about radioactive iodine therapy for cats, including what to expect before, during and after I-131 treament.
Prognosis for cats with hyperthyroidism
The prognosis for both managing and curing hyperthyroidism in cats is excellent, provided there’s no underlying kidney disease. Symptoms usually improve quickly once treatment begins, and the body starts to return to normal – even the heart can recover in early cases.
Final thoughts
I firmly believe that treating hyperthyroidism makes a huge difference for senior cats – and for their owners too. It often means less vomiting, diarrhoea, yowling, aggression, and even fewer litter box accidents.
While some older cats can live with hyperthyroidism, treatment greatly improves their comfort and quality of life. It can be hard for vets to explain everything in a short 15-minute consultation, so hopefully this helps answer some of the questions you might have if your cat has been diagnosed with hyperthyroidism.
Have you cared for a cat with hyperthyroidism? Tell us about your experience – what treatment option did you decide on, and what helped your cat?
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?
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?
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.
Thank you for providing this important information. I had no idea of all the complications hyperthyroidism can cause in a cat’s body.