What is hyperthyroidism?

Hyperthyroidism is a chronic and progressive condition caused by the thyroid gland developing overactive tissue, resulting in the production of too much thyroid hormone. This extra thyroid hormone speeds up the metabolism, producing an often rather dramatic set of symptoms including:

  • Increased appetite (voracious in some cases!)
  • Increased thirst & urination
  • Weight loss and muscle wasting
  • Vomiting and diarrhoea
  • Altered behaviour (grumpiness, irritability, confusion)
  • An unkempt coat

The overactive tissue is usually benign however in some cats, especially those who have had the condition for some time, the growth can become a malignant cancer although this is uncommon. In most cases, the growth is palpable as a thyroid goitre, however sometimes the overactive tissue hides out in the chest where we can’t feel it (called ‘ectopic’ tissue).

How is it diagnosed?

If we suspect your cat may be suffering with an overactive thyroid gland then we will recommend a blood and urine test to diagnose this. The blood test can tell us the specific level of thyroid hormone in the body, along with any changes in the liver, kidneys and red & white blood cells. As the signs of hyperthyroidism can be similar to diabetes or kidney disease, a comprehensive blood and urine test will help to rule these things out as well. High blood pressure can also develop alongside hyperthyroidism, so we recommend testing for this as well.

Occasionally we may pick up on very early thyroid disease on routine blood testing and in this case treatment may not yet be warranted. In most cases, however, treatment is essential to maintain a good quality of life. Not treating the condition is not an acceptable option due to the stress the excess thyroid hormone puts on the body (often resulting in heart failure) and the fact that affected cats are often unsettled, uncomfortable and insatiably hungry despite eating a lot.

How is hyperthyroidism treated?

Once a diagnosis of hyperthyroidism has been established, there are four options for treatment, each varying by success rate, owner effort, patient comfort and financial outlay. With all forms of treatment, there is the potential for underlying kidney disease to be ‘unmasked’. This is because in the hyperthyroid state, blood flow to the kidneys is increased. Once the thyroid level is decreased, the blood flow to the kidneys can drop to a more normal level, making pre-existing (but often previously undiscovered) kidney disease more apparent. As a result, it is important to run blood & urine tests periodically when your cat is receiving treatment, particularly during the initial stabilisation period.

There are four main approaches to managing hyperthyroidism:

1) Radioactive iodine therapy

What’s involved?

A single subcutaneous injection (like a vaccination) of radioactive iodine is given at a specialist centre in Winchester or North London. Due to radiation health and safety, the typical hospital stay is 9-13 days in feline-friendly boarding facilities specifically designed to minimize stress.

Advantages

  • Gold standard treatment with a 95% cure rate requiring no further medication
  • No anaesthetic or surgery is required, making it a very safe option for cats with concurrent heart disease
  • Just a single injection is required in most cases for rapid resolution of symptoms
  • A virtually pain-free, tablet-free method of treating an otherwise chronic and debilitating disease
  • In most cases, beyond a few post-treatment blood tests, there are no further treatment costs
  • Although stabilization on medication prior to treatment is recommended, this is not always necessary so ideal for cats that cannot tolerate the oral medication
  • Minimal risk of the thyroid gland becoming cancerous
  • Minimal risk of recurrence due to ectopic tissue as this is also treated

Disadvantages

  • Occasionally a second treatment is required and in a small number of cats, the thyroid level drops too low requiring additional medical treatment
  • Only a few facilities in the UK are licensed to perform this treatment so some travel is required
  • Some owners find the thought of a long hospital stay troubling (although the vast majority of cats tolerate hospitalization far better than their owners anticipate!)
  • Treatment is irreversible and therefore not recommended for cats with significant pre-existing kidney disease
  • A large upfront payment may not be possible for some owners

Can it cure the disease?

Yes

Cost

Upfront cost is high, overall cost is moderate.

2) Surgical removal of the thyroid gland

What’s involved?

A general anaesthetic is required, so your cat must be stabilized on medication first for several weeks, followed by surgery in our mobile operating vehicle so your cat can return home the same day. Risks and recovery time as per any other surgical procedure. The thyroid gland is in 2 parts – only the overactive half is removed to minimize the risk of dangerous complications.

Advantages

  • Surgery can cure the disease, so it is a good option for younger cats and those that do not tolerate medical treatment
  • We can perform the procedure in our mobile operating theatre outside your home so no travel is required and recovery can take place at home
  • The surgery results in a rapid resolution of symptoms
  • Minimal risk of the thyroid gland becoming cancerous

Disadvantages

  • A general anaesthetic and surgical procedure are required, both of which carry risks especially for cats with concurrent health problems
  • In most cases, 2 surgeries are required, usually 1-2 years apart, as the other half of the thyroid gland also becomes overactive with time
  • Some pain associated with a surgical procedure, but this can be managed with post-operative medications and recovery is usually quick and straightforward
  • Treatment is irreversible and therefore not recommended for cats with significant pre-existing kidney disease
  • Once both glands are removed, there is a small chance that the thyroid level will drop too low requiring additional medical treatment
  • Rarely, the surgery can result in temporary or permanent low calcium levels which can be very dangerous for your cat
  • Although recurrence is rare for cats that have had both halves of their thyroid gland removed, the presence of ectopic tissue may result in ongoing hyperthyroidism

Can it cure the disease?

Yes

Cost

Up front costs are moderate, overall costs are high.

3) Lifelong medication

What’s involved

Once or twice daily dosing of tablets or liquid, or a gel on the ear in some circumstances, is required for the rest of your cat’s life. A blood test is required every 3 weeks until levels are normal, then every 6-12 months once stable.

Advantages

  • No anaesthetic or surgery is required, making it a safe option for cats with concurrent heart disease
  • Treatment is reversible and can be titrated to the most effective dose, allowing for much greater flexibility in cats with concurrent kidney disease, making it a safe option for old, frail cats
  • No hospitalisation or travel is required
  • Giving the medication is relatively easy in most cases
  • It is possible to start with this option then decide to go for curative treatment later (although the sooner the better)

Disadvantages

  • It can take months to stabilise some cats, with increasing doses required as the gland grows bigger. Rarely cats are unable to be controlled on medication
  • Because medication is not a cure and merely masks the symptoms, the disease will continue to progress, increasing the chance of developing a malignant tumour particularly in cats that are younger at the time of diagnosis
  • If the thyroid level is not monitored regularly, incorrect dosing can result in reversible hypothyroidism or recurrent hyperthyroidism
  • Some cats do not tolerate taking medication every day and some owners are unable to give it
  • Side effects of the medication include poor appetite and vomiting (<20%), liver disease, bone marrow suppression and severe skin disease (<5%). These typically resolve once the medication is stopped but can be quite dramatic and uncomfortable at the time
  • Treatment and regular blood testing is required for the rest of the cat’s life, which can be not only frustrating for the cat, but very expensive over time.

Can it cure the disease?

No

Cost

Up front costs are low but overall costs are moderate to high.

4) Dietary management (Hill’s y/d food)

What’s involved?

Your cat is given a food which is very low in iodine, so their body is no longer able to make thyroid hormone. You must feed your cat EXCLUSIVELY this food, no other food sources at all including treats. Like the medication, periodic blood tests are required to ensure the diet is working

Advantages

  • No anaesthetic or surgery is required, making it a safe option for cats with concurrent heart disease
  • As it is just a change in diet, this method is extremely safe, making it a good option for old, frail cats
  • No hospitalisation or travel is required
  • Most cats find the food palatable, at least to start
  • It is possible to start with this option then decide to go for curative treatment later (although the sooner the better)

Disadvantages

  • This method is unlikely to work in cats that have outdoor access or those in multi-cat households (as even a little bit of normal food will prevent the special diet from working)
  • It can take months to stabilise some cats, with a significant number unable to be controlled on the diet alone
  • Because the diet is not a cure and merely masks the symptoms, the disease will continue to progress, increasing the chance of developing a malignant tumour particularly in cats that are younger at the time of diagnosis
  • If the thyroid level is not monitored regularly, incorrect dosing can result in reversible hypothyroidism or recurrent hyperthyroidism
  • Some cats refuse to eat the food, or go off of it in time
  • Not recommended if your cat has another medical condition which requires a different diet
  • There are no significant side effects in the short term, however the long term effects of chronic iodine restriction have not yet been well-studied

Can it cure the disease?

No

Cost

Up front costs and overall costs are low, but the treatment is only effective in some cats the effect may only be temporary.

Which treatment do we recommend?

There are both advantages and disadvantages for all treatment types and we will consider all aspects of your cat’s situation when recommending a treatment method. For an extremely anxious, elderly cat with significant kidney disease, we would probably recommend medication or dietary management. The same may be true for owners without pet insurance where a large lump sum simply isn’t possible, which is absolutely fine.

However, in most cases, if funds allow and especially if your cat is relatively young (i.e. under 15 years of age), we are likely to recommend radioactive iodine therapy as it is generally considered to be the gold standard treatment offering the best results for your cat. No anaesthetic or surgical procedure is required so the risks are minimal and it offers the highest chance of a complete cure, with minimal inconvenience for your cat other than having to sit in a nice hospital kennel for a while.

For owners who find the idea of their cat spending some time in hospital upsetting, we strongly urge you to consider the situation from your cat’s point of view rather than your own. Most cats, even nervous cats, settle into the hospital environment very quickly, especially with the help of specifically trained feline-friendly hospital staff. To date, all of the patients we know that have taken this treatment have coped very well and their owners are now very happy not to have to go through daily medication or regular blood testing. The choice is yours, however, and whichever option you choose we will work with you to provide the best possible quality of life for your cat.

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