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Hyperthyroidism is not usually a painful condition in cats.

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Hyperthyroidism in cats

By Dr Holly Graham BVMedSci BVMBVS MRCVS Veterinarian

Updated on the

Is your cat losing weight, but eating more? Increasingly restless? Then it's possible your pet has hyperthyroidism.

Hyperthyroidism, which is due to an increase in the production of thyroid hormones from an enlarged thyroid gland in a cat’s neck, affects a lot of our feline friends, particularly as they get older. But what is it and how does it affect them? This article will help you understand this condition.

What are the symptoms of hyperthyroidism in cats?

Symptoms of hyperthyroidism can be subtle. Most hyperthyroid cats are middle-aged or older, and mild symptoms can become more noticeable over time. Signs of the condition include:

● Weight loss

● An increased appetite

● Drinking more than usual (and maybe urinating more because of this)

● Restlessness and hyperactivity

● Increased vocalisation

● A poor and scruffy coat

● Mild diarrhoea

● Vomiting

If the disease is severe, you may notice your cat’s heart is beating faster than normal, and they may pant or breathe harder if stressed. Uncommonly, some cats may be weak and have a poor appetite.

Is hyperthyroidism in cats painful?

Hyperthyroidism is not usually a painful condition in cats. The symptoms of hyperthyroidism may cause mild discomfort – for example if diarrhoea is very persistent, but the majority of cats with an overactive thyroid gland are not in pain because of this condition.

What is the prognosis for hyperthyroidism in cats?

The prognosis for most hyperthyroid cats is good, provided it is treated and well controlled. The majority of cats that are treated either medically or surgically will make a complete recovery and live for a long time. It’s important to take your cat to a vet for regular check-ups once diagnosed, as if the treatment isn’t working as it should be, they may become unwell again. Treatment (if not treated surgically) is lifelong.

Do cats need a special diet for hyperthyroidism?

Most cats with hyperthyroidism are fed their normal diet and, if being managed medically or following surgery, don’t require any special diets. If your cat has lost lots of weight prior to treatment, they may require extra food to help them regain some of that weight. Special prescription diets are available for hyperthyroid cats, and this can be used as a treatment option.

These hyperthyroid diets contain restricted levels of iodine, which is used to make thyroid hormones. If the levels are kept lower in the diet, the body should only be able to make the correct levels of thyroid hormones. This can be successful in controlling disease in some cats, but most owners opt to treat their cat with drugs or surgery.

How can I help my cat with hyperthyroidism?

The best thing you can do for your cat, if you think they are hyperthyroid, is to take them to the vet. This condition won’t resolve on its own. Book an appointment with a vet as soon as you can. There are lots of different treatment options available, and it’s up to you to decide which one you think would suit your cat best.

What is late-stage hyperthyroidism in cats?

Early signs of hyperthyroidism in cats can be subtle and more cats are picked up further into the disease. If the disease has been left untreated for a long time, other organs may be affected and there may be complications. Uncontrolled hyperthyroidism can cause cardiac problems, including an increased heart rate and thickened muscular walls in the heart. This can be fatal if not treated successfully. Hypertension is another issue linked to hyperthyroidism and can damage the eyes, heart, kidneys and brain. If you think your cat may be hyperthyroid, get them checked out by a vet as soon as you can.

What happens if hyperthyroidism in cats is left untreated?

While an overactive thyroid gland itself isn’t fatal, the effects of excessive amounts of thyroid hormones on other organs can be. Persistently high thyroid hormones affect the heart, causing it to beat faster than normal and making the muscle wall of the heart thicker. After a while this can cause heart failure. The effects of the hormones can cause hypertension (high blood pressure), which can damage the eyes, kidneys and brain. If left untreated, there are numerous problems that are much more difficult to treat than hyperthyroidism.

When should I put a cat with hyperthyroidism to sleep?

Most cats with hyperthyroidism, once controlled, live happy lives and can live for a long time following their diagnosis. If you think your cat isn’t doing very well once treatment has begun and you’re worried their quality of life isn’t very good, speak to a vet. It may be that there are complications, such as hypertension, or that the dose of their medication isn’t quite right.

These things can be managed and you may notice a huge improvement. But as most cats with this disease are diagnosed as older cats, sometimes there are other things going on as well. If you think your cat is suffering or is no longer enjoying life, sometimes the kindest thing you can do is to let them go.

How to prevent hyperthyroidism in cats

Unfortunately, there isn’t much you can do to prevent hyperthyroidism. Lots of cats as they approach middle age develop the condition and noticing the signs early is important. Feeding your cat a good quality cat food with carefully measured nutrients may help.

How long does a cat with hyperthyroidism live?

Most cats diagnosed with hyperthyroidism live, on average, 3-5 years. Yet this can be longer and these years are usually very happy. Early diagnosis is important in making sure your cat can live as long as possible.

Is hyperthyroidism in cats fatal?

Hyperthyroidism in cats reduces their life expectancy and can cause problems with other organs, like the heart or kidneys. It’s usually these problems that are ultimately fatal. High blood pressure and a higher than normal heart rate cause the heart and kidneys to work harder, and can cause irreversible damage. Most cats with hyperthyroidism, if well controlled, live for at least a few years, so it’s definitely not a death sentence.

What is the best food for a cat with hyperthyroidism?

The best food for your cat depends on lots of things. If your cat is otherwise healthy, with no other problems, a good-quality cat food is all that they need. This could be wet or dry, or a combination. If your cat has other issues going on at the same time, for example kidney disease, it may be that they require special prescription diets to help manage these problems.

If your cat has lost significant amounts of weight following treament, they may need extra food while they regain the weight. If you’re attempting to treat your cat’s hyperthyroidism through diet, with iodine-restricted foods, ask a vet for a prescription diet and advice.

How can I treat my cat’s hyperthyroidism naturally?

Unfortunately, there are no natural treatments available for this condition, and your cat will require lifelong medication, surgery or a prescription diet.

How long does it take for methimazole to start working in cats?

Methimazole is one of the medications used to treat hyperthyroidism. It can be given as an oral tablet, liquid or as a transdermal gel. Unfortunately methimazole doesn’t work instantly and can take a few weeks to reduce the thyroid hormone levels in the blood. A vet may suggest a blood sample a few weeks after starting treatment and, depending on the levels of thyroid hormones, doses may need to be adjusted. Methimazole is a lifelong treatment and, if stopped, then after a few weeks you will likely notice the symptoms of hyperthyroidism returning.

What are the side effects of methimazole in cats?

Most cats on methimazole don’t show any side effects. The most common side effects are lethargy, loss of appetite and vomiting. Cats who are intolerant to methimazole may scratch at their faces – so methimazole can’t be used in these cats. The common side effects usually resolve with reducing the dose, but speak to a vet before attempting to do this yourself. Because kidney disease is often found alongside hyperthyroidism, sometimes signs of kidney disease may be seen once treatment has been started with methimazole.

How much does it cost to treat hyperthyroidism in cats?

Oral medication (tablets or liquids) can become expensive, and cats with hyperthyroidism require lifelong treatment. Surgical treatment or radioactive iodine therapy is very expensive initially – but often this is just a one-off cost. Pet insurance can be very helpful for cats with hyperthyroidism, so this is something to consider when getting a kitten or an adult cat. Speak to a vet, if you have concerns about the costs of your pet’s medication.

How is hyperthyroidism treated in older cats?

Both old and younger cats can be treated with the same methods. The options for treatment include: methimazole or carbimazole medication (tablets/liquids/transdermal gels), surgical removal of the affected thyroid gland or radioactive iodine therapy. Older cats may not be suitable candidates for surgery, so most are managed with oral medication. Older cats are more likely to have concurrent problems and, once their thyroid is successfully managed, may require medication for other things – like kidney disease.

Can a cat with hyperthyroidism gain weight?

Thyroid hormones play an important role in regulating the body’s metabolic rate. If there is an excess of these hormones, the metabolic rate is increased. This means that most cats lose weight, or find it difficult to gain weight. Once your cat’s thyroid levels are normal, it is completely possible for them to gain weight again.

Why do hyperthyroid cats yowl?

The thyroid hormones overproduced in this condition can have effects on the nervous system, causing behavioural changes in cats. Restlessness and yowling are the result of this. Once levels are brought back to normal, this should resolve.

When should I see a vet?

If you notice anything changing with your cat, whether this is behavioural or signs of ill health, consult a vet. Signs of hyperthyroidism can be subtle and could be symptoms of other problems, but a vet will be able to rule problems in or out.

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