Mrs Thomas hadn’t been particularly concerned about her cat, Wilson, when she booked his old-cat check up with vet Lucy. In fact, she was particularly pleased that his appetite seemed to be getting better with age rather than tailing off as had been the case with her previous cat, Hank, who’d sadly succumbed to kidney failure. Wilson did seem to be thinner than usual, but Mrs Thomas had put that down to simply old age; he was 16 after all. She’d also been considering cancelling his pet insurance; as surely he was less likely to need it now at his age?

Good news… or bad news…?

Lucy called them in and placed Wilson on the scales. What had seemed to be a bit of slimming down, was now revealed to be a drop of over 10% of bodyweight; from 4kg to 3.5kg in just a few months. As Mrs Thomas proudly told Lucy tales of Wilson eating two pouches in a sitting and even trying to swipe the toast crusts in the morning, Lucy’s mind was already ticking. 

She asked Mrs Thomas whether Wilson had become more vocal recently or had seemed more hyperactive. Now she thought about it, Mrs Thomas realised that yes, he had started coming into the bedroom at 2am and meowing loudly, then running up and down the stairs for no obvious reason. She had been quite pleased that even at his age, he was still behaving like a kitten but looking at Lucy’s face, she was beginning to understand that when combined with the weight loss despite having a very good appetite, that maybe this wasn’t normal and could be a sign of a potential issue. 

Lucy then placed her stethoscope on Wilson’s chest. She was barely able to keep up with the heart rate; but managed to calculate it to be at least 220bpm, well above the normal range. 

By now, Lucy had a pretty good idea what could be going on with Wilson. And that maybe he wasn’t quite the perfect picture of health his owner thought he was. She explained to Mrs Thomas that she thought Wilson may have a condition called hyperthyroidism. Mrs Thomas’ heart sank – that sounded serious. 

What is hyperthyroidism?

The thyroid gland is actually a pair of glands that are found in the neck, either side of the windpipe. They produce two forms of thyroid hormone, T3 and T4, which help to regulate the body’s metabolism. In older cats, sometimes one, or even both, of these glands can begin to enlarge due to a benign tumour which causes them to produce an excessive amount of these hormones. This will, in turn, increase the cat’s metabolism and produce the classic symptoms as demonstrated by Wilson. Some cats will also begin to drink more and urinate more; have an ‘unkempt’ appearance with a poor hair coat; or will have vomiting or diarrhoea. This increase in metabolism will put stress on the heart and can also raise the blood pressure. So it is important to diagnose and treat these cases as soon as possible. 

First steps

Hyperthyroidism is easy to diagnose in cats, requiring only a blood test. It is advisable to run a full blood screen initially to make sure there are no complicating factors, and also to check the kidney values. Having a high thyroid level can actually mask the signs of renal failure as it falsely increases the filtration rate through the kidneys. This means that the usual measures of kidney function on a basic blood test can appear normal. 

Even though he wasn’t particularly happy about having his blood taken, Wilson eventually allowed Lucy to do her job and the sample was sent to the laboratory that day. Mrs Thomas was given her own homework to collect a urine sample from Wilson (again, sometimes easier said than done!). And when she brought it back in the following day, Lucy had the blood results ready. 

The testing had proved Lucy right. Wilson had an excessive level of thyroid hormone in his blood, confirming a diagnosis of hyperthyroidism. Thankfully, the rest of the measurements were generally normal, bar a slight increase in one of his liver enzymes which is very common in cases of hyperthyroidism. And the kidney values were reading towards the upper end of the normal range. The urine sample showed that, for now, the kidneys appeared to be working adequately. But this would need to be monitored as Wilson’s treatment progressed. 

The next step was to discuss the treatment options for Wilson and Mrs Thomas. As Lucy began going through what was available, Mrs Thomas began to feel very thankful that she hadn’t cancelled Wilson’s insurance just yet. 

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What now?

Think of a treatment type and there is likely to be a use for it in treating hyperthyroidism! There are plenty of options to suit any case. Some are more invasive than others, but they obviously all come with their own costs. 


Oral treatment with tablets is probably the most common treatment for hyperthyroidism. The tablets are typically very small and should be dosed once or twice daily depending on the cat’s requirements. They can easily be given in food but should not be crushed, as the drug itself can potentially be damaging to certain groups of people and gloves ought to be worn when handling them. 

Oral liquid 

As sometimes it can be difficult to get cats to take tablets, an oral formulation is available. However, it should be dosed directly into the mouth of the cat and not mixed with food. The same precautions should be taken as with the tablets. 

Transdermal gel 

This is the same drug in a gel form that is actually smeared onto the skin of the inner surface of the cat’s ear pinna. It is then absorbed through the skin and is thought to be as effective as the oral treatments. It is, however, an off-licence treatment, meaning it should only be selected when other treatment options are not possible. 


There is one prescription diet available that aims to reduce the amount of thyroid hormone produced by the body by restricting iodine which is vital in the production of the hormones. In order for it to be successful, it ought to be the only food the cat eats, meaning that cat treats, ‘human’ food, and even the local wildlife are off the menu. Long term use has yet to be investigated. 


Because hyperthyroidism is caused by a benign tumour on the thyroid gland, removal of said gland is one, very successful, treatment option. The surgery is commonly performed in first opinion practice with minimal complications. It does, however, require a general anaesthetic which in older patients does come with increased risks. It is advisable to treat potential surgical cases with medical therapy first to try to reduce the thyroid hormone level which will make them more stable to undergo surgery. 

The main benefit of surgery is that there shouldn’t be any need for daily medication afterwards. The downsides are that, fairly commonly with time, a tumour will begin to also grow in the other gland of the pair, requiring further surgery to remove this too. Up to 20% of hyperthyroid cats actually also have ‘extra-thyroidal’ tissue elsewhere in the body, often in the chest cavity, which obviously isn’t easily accessible by surgery, and which will continue to produce thyroid hormone. 

Radioiodine treatment 

This is classed as the ‘gold standard’ of treatment for many practitioners. This is a form of radiation therapy which specifically targets any tissue that is producing thyroid hormone. It is seen as the most thorough and long-lasting treatment option available, but is also the most expensive as cats must be referred to a specialist treatment unit. Because of the radiation, treated cats must also remain in the hospital for at least a week and there will be further restrictions on where they can go and how their waste must be managed at home for the first few weeks after discharge. 

Choices, choices, choices

By this point, Mrs Thomas was looking quite bewildered. Lucy reassured her that any of the treatment options would help Wilson and that most clients opt to at least start medical management with tablets, with a view to considering the more permanent treatments once he is more stable. Whatever option is chosen, it’s important to monitor repeated blood samples. She arranged to send Mrs Thomas away with a month’s worth of tablets, an appointment for the next blood sample in three weeks and estimates for surgery and referral for radioiodine treatment. 

Thankfully, it turned out that Wilson was quite happy to take his tablets, as long as they were delivered in the local supermarket’s finest roast chicken. And when Mrs Thomas presented him to Lucy three weeks later, she was very pleased with his progress. Wilson had gained some weight, his coat was glossy, and he seemed much more content at home. When the latest blood results came back, they proved that he had indeed improved, and his thyroid hormone levels were now within the normal range. 

Lucy had more good news too 

She had been speaking to the closest referral centre that could provide Radioiodine therapy and they had an opening to see Wilson in a few weeks’ time. The bill was expected to be the best part of £3000, but Mrs Thomas was thrilled. She had considered all the options available and having spoken to her insurance company, they had confirmed that Wilson’s treatment would be covered. Even though Mrs Thomas suspected that Wilson would be quite happy to carry on with the twice daily dose of chicken, she felt a more permanent solution was the better option. 

A happy ending

Wilson underwent his Radioiodine treatment, thoroughly enjoying his first class stay in the feline unit for ten whole days. He recovered very well but still required regular check-ups with Lucy, including blood samples, urine samples, and blood pressure measurements to ensure that there were no long-term complications. Six months later, Wilson had regained the weight he’d lost and was calm and content at home with Mrs Thomas. Lucy was happy with his progress, though, as his thyroid level dropped, it did unmask the early stages of renal failure. Thankfully, Wilson found he quite liked the veterinary Renal diet that Lucy suggested to help to support his kidney function. And even better, he was still occasionally allowed to indulge in his favourite treat – chicken. 

Further reading:

Some details changed to protect Mrs Thomas’ privacy