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An overactive thyroid in cats

Lots of older cats have an overactive thyroid. This condition is called hyperthyroidism, which means that your cat’s thyroid gland makes too much thyroid hormone. In this article, the thyroid as an organ is explained as well as the consequences of an overactive thyroid for your cat. It’ll also go into treatment options.

Your cat’s thyroid

The thyroid is an organ with two glands, one on either side of your cat’s trachea. Located near the thyroid glands are the parathyroid glands. The thyroid regulates your cat’s metabolism.

What is an overactive thyroid?

As the word implies, the thyroid of a cat with hyperthyroidism is too active. It makes too much thyroid hormone, which causes an elevated heartrate, a blood pressure that is too high, a metabolism that is too fast (often paired with diarrhoea) or behavioural changes. Hyperthyroidism is often caused by a benign tumour in the thyroid.

Symptoms in cats

The following ae possible symptoms of hyperthyroidism:

  • Losing weight despite a good appetite.
  • Drinking and urinating more.
  • Straggly coat.
  • Behavioural changes. Many cats become more restless and active than usual. They also often find cooler places to lie down and start panting.
  • Sometimes vomiting and diarrhoea.
  • The thyroid becomes enlarged and can be felt in the neck. This is impossible with a healthy thyroid.

Because an overactive thyroid often causes a higher blood pressure in cats other symptoms my become apparent, such as a reduced heart function, reduced kidney function and even blindness.

How does the veterinarian diagnose hyperthyroidism in my cat?

The symptoms the cat displays often already indicate what is happening. When you can feel the thyroid in your cat’s neck, the diagnosis becomes even more probably. The diagnosis can be confirmed through a blood test. This tests several bodily functions, such as the liver function and the kidney function, as well as the thyroid panel.

Sometimes a cat already displays symptoms of an overactive thyroid, even though the blood test shows normal levels of the thyroid hormone. In this case, a repeat blood test after six weeks is advisable. Many veterinarians can do this test in their own surgery.

Aside from a blood test, measuring the blood pressure is also important. As mentioned before, this is often too high which can have great consequences for your cat’s physique. A too high blood pressure also needs to be treated to cure or prevent other ailments.

How can my cat be treated?

When your cat is diagnosed with hyperthyroidism, a treatment plan is created. There are several treatment options for a cat with a hyperactive thyroid. These are dependent on a few different factors, such as:

  • Your cat’s symptoms.
  • Is it a benign or a malignant tumour?
  • Is the tissue only present in the thyroid or has it spread to other places? This is called ectopic thyroid tissue. In this case, an operation will be more difficult because it’s possible not all tissue can be removed.
  • Your cat’s age.
  • Your cat’s overall health and whether there are any additional problems.
  • Whether it is easy to give your cat medication.

What are the treatment options?

  • Treatment with medication: there are tablets that lessen the production of the thyroid hormones. This is the most common treatment. Being able to administer pills to your cat is a prerequisite for this treatment.
  • Removal of (part of) the thyroid through surgery: this is a difficult operation and not every veterinarian does it. Furthermore, it is possible that not all thyroid tissue in other sports can be removed. It is advisable to perform a preliminary special examination using a contrast medium to find out where the active thyroid tissue is located. This can prevent an unnecessary operation. When removing the thyroid it is very important to leave the parathyroid glands. These serve an important function and are indispensable. A complication of the operation is the possibility of the thyroid tissue growing back or of the thyroid making too little thyroid hormone resulting in your cat needing medication anyway.
  • Treatment with radioactive iodine: this radioactive iodine ends up in the diseased (active) part of the thyroid and will destroy the diseased tissue. This is a specialised treatment and your cat will need a referral for it. After the diseased tissue is treated, the healthy thyroid tissue will become active normally again and further treatment with medication won’t be needed. Your cat will be radioactive for a couple days after treatment. Your cat will need to stay in a special room for at least eight days. This makes this treatment not suitable for cats with difficulties eating or that needed further medication. Sometimes repetition is necessary.

Thyroid cat food: Hill’s Y/D

  • Treatment with special food: there is a special cat food without iodine, Hill’s Y/D. The iodine is necessary to make the thyroid hormone. Often times it is unnecessary to combine this food with medication or another treatment. It is important that your cat only eats Hill’s Y/D. This makes it most suitable for inside cats. A drawback is that not all cats accept the food.

What should happen if my cat’s blood pressure is too high?

If your cat has both an overactive thyroid and a high blood pressure, these will need to be treated separately. Sometimes the blood pressure will normalise when the thyroid is under control, but other times lifelong medication for high blood pressure is needed.

My cat’s treatment plan has been implemented, now what?

If your cat is treated for the thyroid, it is important to take him to your vet for regular check-ups. This is the case for all types of treatment! It is imperative that your vet does the following check-ups every 3-6 months:

  • Physical examination and weight check
  • Blood test for the thyroid panel, but also a blood panel (red and white blood cells), the kidney and liver functions. Both an overactive thyroid and the treatments can affect this.
  • Blood pressure check

Do you think your cat has an overactive thyroid? Take your cat to your veterinarian for a check-up! A fast diagnosis and treatment can be the key to a long and happy life for your cat.

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