Hyperthyroidism in cats

Hyperthyroidism is when the thyroid glands in your cat’s neck produce too many hormones. This can cause the glands to enlarge and make your cat’s neck look swollen. Thyroid hormones help regulate metabolism, so hyperthyroidism can cause a lot of other symptoms and conditions. 

Most of the time, enlarged thyroid glands are caused by​ the growth of​ a ​benign​ tumour​ or growth​ called​ an adenoma​. But there are some very rare cases of malignant tumours ​(tumours that spread to other parts of the body) ​that can cause hyperthyroidism.  

Other factors such as diet and environment have also been thought of as potential contributors to hyperthyroidism, but no one knows why this happens. 

Early symptoms can be very subtle, but it’s always worth keeping your paw on the pulse as these will often get worse as the disease progresses.  

Main symptoms include: 

• weight loss 
• increased appetite 
• increased thirst 
• hyperactivity and vocal behaviour 
• vomiting and diarrhoea  

Less common symptoms are: 

• one or two lumps in the​ upper part of the​ neck 
• a fast heartbeat 

​​Vet Dr Corinne says “The symptoms of hyperthyroidism can be vague and similar to many other conditions we see in old age, like renal disease or diabetes. This is why a vet check and blood tests are so important to find the exact cause. As a veterinarian I always recommend a yearly health check and blood test in any patient over eight years old.”

If you think your cat has a problem with their thyroid, speak to your vet. They’ll be able to perform ​a health check on your cat​ to see how likely that is.  

A physical examination might include: 

• checking your cat’s neck for enlarged thyroid glands 
• taking their blood pressure and checking their heart rate 

If hyperthyroidism is suspected, ​the most common form of diagnosis is a blood test to measure high levels of thyroid hormones.  ​ 

​​If your vet isn’t sure about the results of the blood tests, they can refer your cat to get a technetium scan. This can find exactly where the gland is enlarged.​ 

Your vet might also do more tests to check your cat’s general health as the thyroid can affect the whole body. This may include looking at kidney and liver functions and ​an ​echocardiogram for their heart.​ These are important when thinking about which treatment option is best for your cat. ​ 

There are four main types of treatment for cats with hyperthyroidism. But every cat is different, so your vet will be able to advise the best course of action for your feline friend. 

Oral medication 

Anti-thyroid drugs slow down your cat’s thyroid glands so they don’t produce and release as many hormones. These are most often taken twice daily, which can be difficult to keep up with, especially as it’s a lifelong treatment. Your cat will also need regular blood tests done​ for the rest of their life​. This is to make sure the medication is working and not having negative side effects on their kidneys. 

Outlook

Treatment with anti-thyroid medication can be adjusted depending on how effective it is. Your cat should experience a reversal of any hyperthyroid symptoms for as long as they stay on the medication.​ If you stop the medication, or give too low a dose, the symptoms will come back. ​ 

Surgery 

Surgery – called a thyroidectomy – involves removing the enlarged gland tissue. This can mean a permanent cure (or at least a long-term cure) as the tissue is no longer there. It can re-develop later down the line if any remaining tissue becomes infected.  

With surgery comes risks as your cat will have to be put under a general anaesthetic. So it might not be the best route for older cats or those with additional health needs. There’s also the possibility of damaging the parathyroid gland which sits right next to the thyroid. This might leave your cat needing ​lifelong ​treatment for low calcium levels​, and this medication is expensive​.​ Another risk with surgery is that removal of the whole gland can cause thyroid levels to drop too low, and supplementation with tablets are needed. ​ 

Outlook

After surgery your cat shouldn’t show any signs of hyperthyroidism. There is a small risk that if just one gland was removed that the other gland may show signs later down the line. Your cat ​still needs to have regular​ blood test​s​ to make sure their thyroid hormones stay at normal levels.  

Radioactive iodine therapy 

Radioactive iodine therapy may sound daunting, but it’s a safe and effective treatment. 

A vet injects a small dose of iodine under the skin, which is absorbed directly by the thyroid without affecting other organs. This targets and inactivates the overactive thyroid tissue. 

For most cats, a single injection can provide a long-term cure. While not all vet clinics offer this treatment, your vet can refer you to a specialist clinic within a reasonable distance. 

Outlook

Many cats experience a complete reversal of symptoms after one radioactive iodine injection and can go on living their adventurous lives. Occasional blood tests may be recommended to check symptoms have not returned.  

Dietary therapy 

A​nother​ treatment for hyperthyroidism is a low iodine diet, which prevents the thyroid from becoming overactive. This is usually available on prescription from your vets.  

Outlook

If your cat is fed an exclusively low iodine diet, then they shouldn’t show symptoms of hyperthyroidism. If you change their diet, then symptoms may come back.  

If they are a hunter, or snack on anything other than their special diet, a low iodine diet may not be enough to control their thyroid levels.  

This treatment is normally best suited to indoor cats. As with medications, regular blood tests are recommended to make sure the thyroid hormones are in the normal range.  

We’re on a mission to kick pet prejudice to the curb, so Petgevity will consider all conditions when offering cover for your cat.  

We’ll need to know: 

• what medical conditions they’ve had in the last two years 
• their current health status ​​     ​ 

Find out more about Petgevity’s cat insurance for pre-exsting conditions.