As cats become older, they can develop hyperthyroidism. Find out everything you need to know about the causes, symptoms and treatment of this disease.
Feline hyperthyroidism commonly affects middle-aged or senior cats. Symptoms develop slowly, so it’s a good idea to keep a close eye on your cat as they age and speak to your vet if you’re concerned.
What is hyperthyroidism in cats?
Hyperthyroidism occurs when the two thyroid glands in a cat’s neck start to enlarge and produce excess amounts of thyroid hormones. These hormones help control metabolism, and when there’s too much of these in your cat’s bloodstream, their metabolic rate and bodily functions speed up.
What causes hyperthyroidism?
This disease is relatively common in senior cats. Usually it’s caused by benign swelling, but in rare cases it’s triggered by a cancerous growth. It’s important to be aware that because of the role the thyroid gland plays in the body, some cats may develop heart disease and high blood pressure.
However, some breeds seem to have a lower incidence of thyroid issues in cats, including the British Shorthair, Siamese, Persian, Abyssinian, Tonkinese and Burmese.
Hyperthyroidism in cats: symptoms
In the early stages of this disease, the symptoms can be very subtle and easy to miss. But early intervention increases your cat’s chances of living with hyperthyroidism.
Keep an eye out for the following five symptoms, and if you’re concerned about thyroid issues in cats, it’s always best to book a vet appointment as soon as possible.
Your cat is eating all the time, but still losing weight
Polyphagia – weight loss despite an increased appetite – is a classic sign of feline hyperthyroidism.
If your cat is always hungry and asking for more food, yet never puts on weight, hyperthyroidism may be the cause. Checking your cat’s body condition score regularly can help you keep an eye on their weight. Speak to your vet practice for more advice on how to check your cat’s body condition score.
Drinking more than normal
Excessive thirst is typical of many health conditions that affect cats, including kidney disease. But when combined with polyphagia, your vet may want to check for hyperthyroidism and feline diabetes.
An increased heart rate
An overactive thyroid makes your cat’s heart work too fast. You may feel this when you pick them up and their heart races. This is the main reason for the urgent need to diagnose hyperthyroidism as early as possible, to reduce the chances of heart failure and hypertension developing.
A ‘scruffy’ appearance
Cats with hyperthyroidism develop an unkempt and scruffy coat, which may also look dull. Longhaired cats can develop mats. You might only realise this has happened when you look back at old photographs. This may not be a sign of simply ageing, but one of hyperthyroidism.
Diarrhoea and vomiting
Cats with hyperthyroidism may develop diarrhoea, vomiting or both. Some also urinate more frequently, sometimes outside their litter tray. If you don’t know where your cat toilets, keep an extra careful eye on their behaviour for signs of diarrhoea.
Behaviour change
Affected cats often show signs of restlessness or become cranky or aggressive, so be aware of any behaviour changes, including increased vocalising, particularly at night.
How is hyperthyroidism in cats diagnosed?
If you’re concerned your cat may have hyperthyroidism, take them to the vet as soon as possible. They’ll check the cat’s neck for an enlarged thyroid gland and run some blood tests to determine your cat’s thyroid hormone levels. A second test may be needed to confirm the diagnosis.
The symptoms of hyperthyroidism in cats is similar to other conditions such as kidney disease or diabetes. Hyperthyroidism can also mask the early signs of kidney disease, so your vet may carry out further tests to rule out these conditions at the same time.
Hyperthyroidism in cats: treatment
If your cat is diagnosed with hyperthyroidism, your vet will likely recommend four possible treatment options: medication, surgery, radioactive iodine therapy or dietary therapy – as well as discuss what you can do to support them at home. Treatment will be recommended based on the age and health of your cat.
Medication
This is the most common treatment option and involves giving your cat medication up to three times per day. The medication comes in the form of tablets, or liquids applied to the skin. The medication doesn’t cure the disease, but provides either short-term or long-term control of feline hyperthyroidism by blocking excessive hormone production. It’s usually given as a tablet, liquid or gel daily.
This option requires lifelong medication and regular vet check-ups to monitor kidney function. If you forget to give your cat their medication, the symptoms return. Side effects of medication can be experienced by some cats, including vomiting, fever and lethargy.
Surgery
This removes any enlarged sections of your cat’s thyroid glands. Your vet will explain the procedure, but usually medication is needed for around three weeks before the operation. After your cat has recovered from the operation, they won’t need any ongoing treatment.
The relatively straightforward surgical procedure has a good success rate and the likely outcome is a permanent cure. However, there are risks to older cats undergoing general anaesthetic, and a risk of inadvertently damaging glands close to the thyroid that stabilise blood calcium levels.
Radioactive iodine therapy
This can be used to break down your cat’s thyroid glands without the need for invasive surgery. It cures hyperthyroidism, has no serious side effects, and doesn’t require anaesthesia.
During this treatment, radioactive iodine is injected into the body. The iodine works when it is absorbed into the thyroid gland, deactivating excessive tissue. Normal hormone levels return within a couple of weeks. Your cat will need to stay quarantined at a specialised licensed facility until the radiation levels are considered safe. Only certain locations are permitted to handle and inject a radioactive substance, but in 95 per cent of cases treated using radioactive iodine therapy, cats are cured within three months.
A low-iodine diet can also sometimes control the symptoms of feline hyperthyroidism – but you need to take care that your cat doesn’t eat any other types of food. If you have a multi-cat household, or your cat spends a lot of time outdoors, this may not be the best choice. Research is still ongoing into the effects of long-term iodine restriction on overall health, so discuss this with your vet first.
If you notice any symptoms of hyperthyroidism in your cat, it’s always best to speak to your vet straight away. If you have cat insurance with Petplan, you can speak with someone about thyroid issues in cats via our Pet Expert Chat. Just log into your My Petplan account and head to the My Support area to access.
Once their condition is diagnosed and treated, cats with hyperthyroidism can live happy and healthy lives.
Hyperthyroidism in cats: Barney’s story
Kay Thomas knew there was something wrong with her 17-year-old cat Barney when the once affectionate cat was meowing constantly and finding it hard to settle. Barney was also losing weight, despite appearing to be hungrier than ever, and he was drinking more water.
After a full health check at the vet, including blood tests, Barney was diagnosed with hyperthyroidism. ‘When we got the diagnosis, I was relieved,’ admits Kay. ‘We have human family members with thyroid issues, so I knew it could be managed.’
The vet tried medication to control the condition. The first medication had side effects which saw Barney over-grooming and vomiting. A change to a different course of medication, monitored every five to six weeks with blood tests for the first few months, brought the hyperthyroidism under control.
‘Giving the medication on an empty tummy makes him sick, so we serve a little bit of food for breakfast, then give him a tablet, then give him a bit more food,’ explains Kay. ‘Initially, we also struggled to get him to take it. We tried rolling the pill in turkey or chicken breast and mixing it with tuna, which didn’t really work. We’ve now found a cat pill pâté to roll it in, which is sticky and a bit smelly, but very effective!’
These days Barney is back to his old self. After a year of treatment and eating a diet recommended by his vet, his weight has stabilised and his fur is glossy again. ‘In all the years we’ve had him, Barney has been a lovely pet and I want to make sure he stays relaxed, healthy and comfortable in his old age,’ says Kay.
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