Hyperthyroidism in Cats (Symptoms, Causes & Treatment)

Hyperthyroidism is an extremely common condition in cats. It’s estimated that over 10% of all senior cats will develop the disorder.¹ hyperthyroidism occurs when a cat’s thyroid gland overproduces thyroid hormones. The increase of thyroid hormones sends your cat's body into overdrive, pushing their metabolism, heart rate, and other metabolic functions to the max.

Hyperthyroidism is extremely hard on your cat’s body and is a serious condition. If left untreated, it can be deadly. The good news is that there are not just one but several effective methods of treatment and , in some cases, the disease can be completely cured.

Looking to learn more about hyperthyroidism in cats? Read on to learn all about this common disease, its causes, signs, treatment, and more. Use the links below to jump ahead to a section of your choosing.

• What is Hyperthyroidism?
• Symptoms of Hyperthyroidism in Cats
• What Causes Hyperthyroidism?
• Diagnosing Hyperthyroidism in Cats
• Treating Hyperthyroidism in Cats
• FAQS
• Final Notes

What is Hyperthyroidism?

In order to understand hyperthyroidism, it’s important to first understand what a thyroid is and the role it plays. All mammals have a thyroid gland. It plays an essential role in producing hormones that affect metabolism, growth, heart rate, weight, reproduction, the nervous system, and more. The thyroid affects nearly every organ in the body and is central to your cat’s health and wellbeing.

Hyperthyroidism in cats is a condition characterized by an enlarged thyroid. When enlarged, the thyroid produces excess thyroid hormone, acting like a gas pedal for your cat's metabolic rate, influencing many bodily processes. When your cat’s thyroid hormones increase, the rate of their metabolism spikes, along with heart rate, activity levels, and more.

Signs of Hyperthyroidism in Cats

When it comes to cat skin allergies, it’s usually not hard to spot a problem. Hyperthyroidism is quite different. One of the tricky things about hyperthyroidism is the potential difficulty in diagnosing it.

The signs of feline hyperthyroidism can be so similar to a host of other conditions, making its identification challenging. Additionally, signs of hyperthyroidism usually begin subtly and can initially be hard to miss. As the condition progresses, your cat’s signs will become more severe.

There are a few common signs that cat owners can keep an eye out for. If your cat is eating more but losing weight, that may be a sign of hyperthyroidism. You may also notice that your cat is drinking and urinating more than normal. Your cat’s coat may also be an indication of thyroid issues. Cats with hyperthyroidism often have greasy, unkempt-looking coats.

Hyperthyroidism can also have a significant impact on your cat’s heart health. The condition causes your cat’s heart to pump more quickly, spiking your cat’s blood pressure. Your cat’s heart muscles then must thicken to keep up with its demands, which can lead to heart failure when left untreated. In serious cases, blood pressure may spike so significantly that the retina detached from the back wall of the eye, causing sudden blindness.²

Additional signs of feline hyperthyroidism may include:

• Increased heart rate
• Vomiting
• Diarrhea
• Restlessness/hyperactivity
• Aggressive behavior
• Difficulty breathing
• Weakness
• Mood changes/depression

If you suspect your cat may have hyperthyroidism, the best thing you can do is to consult your vet. They can evaluate your cat’s health and help determine whether they may be suffering from hyperthyroidism.

What Causes Hyperthyroidism?

Experts seem to have a few theories about what may cause hyperthyroidism. In most cases, the thyroid gland becomes enlarged due to a tumor on one or both of their thyroid glands. Of these, 97% are benign tumors known as adenomas, while the remaining 3% are cancerous tumors.³ Research has also identified certain dietary or chemical factors that may play a role in hyperthyroidism.⁴

As far as breed goes, there is also little correlation with hyperthyroidism. Cats of all breeds can experience hyperthyroidism, and the numbers are similar across most breeds with the exception of Siamese cats, Burmese, Persian, Abyssinian, and Himalayan cats. These cats tend to have lower cases of hypothyroidism.

as far as experts can tell. In addition, there is some evidence that Kinkalow cats have higher rates of hyperthyroidism.

The one thing that seems to be a fairly common factor when it comes to hyperthyroidism in cats is age. Most cats who experience hyperthyroidism are on the older side, with the average age of cats who have hyperthyroidism being 12 and only about 5% of cats with hyperthyroidism are younger than 10 years old.

Diagnosing Hyperthyroidism in Cats

If you notice signs of feline hyperthyroidism in your cat, the first step to take is to contact your vet. They can help to properly assess your cat’s health and determine whether action is needed.

The following exams and tests may help your vet determine whether your cat has feline hyperthyroidism:

• Physical exam: Checking the size of your cat’s thyroid is a good way to gauge its function, so this is a common first step for vets. The thyroid gland is located in the neck, which means your vet can perform a physical exam to see if there’s anything obviously wrong with your cat’s thyroid. They may feel around your cat’s neck and throat area or look for any signs of enlargement. If they do spot signs, further testing is needed. An enlarged thyroid gland can be a sign of a goiter, which doesn’t necessarily mean your cat has a thyroid problem.
• Blood test: While an ear infection may be diagnosed with physical tests, hyperthyroidism can only be diagnosed using a blood chemistry panel. Your vet will run tests on your cat’s blood to determine thyroid hormone levels. If your cat’s blood shows high levels of thyroid hormone, it’s possible they’re suffering from feline hyperthyroidism.
• Urine test: While there is no direct urine test for hyperthyroid. Testing your cat’s urine can provide valuable information. Cats with hyperthyroidism often have protein in their urinary. This could be an indication of concurrent kidney disease. As both conditions are typically occur in older cats, it is common for a cat to have both conditions.
• Heart ultrasound: Hyperthyroidism can impact heart health significantly, causing the heart rate to increase and the heart to enlarge. A veterinarian may look for signs of this using an ultrasound.

If hyperthyroidism is suspected, your vet may preemptively check other vital organs, too. Because hyperthyroidism puts your cat’s body into overdrive, and organs like the kidneys can be seriously affected. Checking these organs can help your vet determine any secondary signs that need to be addressed during treatment.

Treating Hyperthyroidism in Cats

Good news: there are plenty of options when it comes to treating hyperthyroidism in cats. Just like an itchy cat can be cured with skincare and avoiding allergenic foods, hyperthyroidism can be treated with several options.

Medication

Thyroid medications can offer an extremely effective first line of defense against hyperthyroidism. These drugs, known as antithyroid drugs, work by lowering the amount of thyroid hormones released by the thyroid gland. They do so thanks to a drug known as methimazole, an antithyroid medication for humans and cats alike.

Antithyroid medications do not cure hyperthyroidism. However, they can either be given long-term, or can be used to lower thyroid hormone levels before another treatment is administered.

Common types of antithyroid medication include:

• Felimazole
• Felanorm

Your vet will give you specific instructions on how to administer these drugs. It’s also generally recommended that your vet perform quarterly blood tests while your cat is on the drug as well as monitor your cat’s blood pressure.²

Common side effects of methimazole include:

• Decreased appetite and weight loss
• Lethargy
• Skin issues and hair loss
• Anemia
• Vomiting
• Diarrhea

It’s also recommended that your vet pay special attention to your cat’s kidneys while they are being administered methimazole. While hyperthyroidism can cause kidney disease, its secondary signs like increased blood flow can also help your cat’s kidneys continue to function even with kidney disease. Once methimazole helps their bodies function normally, blood flow to the kidneys will decrease and kidney function may worsen.

Radioactive Iodine Therapy

Radioactive iodine therapy is perhaps one of the easiest and most effective treatments for hyperthyroidism. Nearly 95% of all hyperthyroidism cases are cured within 3 months of starting radioactive iodine therapy.⁴

Radioactive iodine treatment addresses hyperthyroidism by injecting a single dose of radioactive iodine beneath the skin. It’s absorbed into the bloodstream and taken to the thyroid gland, where it can destroy any excess thyroid tissue without harming any of the primary thyroid tissue or causing any serious side effects. You can expect your cat’s thyroid function to return to normal within a few weeks of treatment.⁴

With such a simple and effective treatment, you may be wondering why other options even exist. The primary drawback of radioactive iodine therapy is its involvement of radioactive materials. To administer the therapy, a facility must be specially licensed to use radioactive materials. Plus, while radioactive iodine therapy is considered extremely safe for your cat, it may be harmful to anyone who comes into contact with your cat. That means your cat must remain isolated in a veterinary hospital until they meet certain thresholds in terms of radiation levels. This is typically a period of 3-5 days.

Surgery

Another method of treating hyperthyroidism in cats is to simply remove the problematic gland. Thyroid surgery can be a permanent cure for hyperthyroidism and is a fairly straightforward surgery. However, it can pose some risks for cats with other conditions, especially those associated with age like heart and kidney problems. Additionally, there is a minimal risk of damaging the parathyroid gland during surgery, which can have serious side effects.

Dietary changes

In some cases, treating your cat’s hyperthyroidism may be as simple as changing their food. Some research has shown that reducing iodine levels may slow down the production of thyroid hormone. Several cat food makers offer prescription diets with reduced iodine to help with signs of hyperthyroidism.

This method of treatment does have its downsides. There is some concern that restricting iodine long-term may have some negative ramifications and might even make hyperthyroidism worse.⁴ If you’re interested in trying this therapy, it’s a good idea to have a conversation about it with your vet. They can offer personalized nutritional advice and help determine whether this is the right hyperthyroidism treatment for your cat.

FAQS

How long does a cat live with hyperthyroidism?

While hyperthyroidism affects your cat’s metabolism, it also changes the way the rest of your cat’s body works. The physical changes caused by an overactive metabolism can lead to heart and kidney failure, which is why most cats who receive treatment for hyperthyroidism only live about 3 to 5 years. However, advancements in treatment for hyperthyroidism in cats mean you can make those 3 to 5 years enjoyable for your cat.

Do cats with hyperthyroidism suffer?

Left untreated, hyperthyroidism will cause several issues that affect a cat’s quality of life. Cats who experience hyperthyroidism may also experience vomiting and diarrhea, which are unpleasant side effects of this condition. Your cat may also lose weight despite eating more, and its hair may be matted and greasy as a result of a hyperactive metabolism.

With proper treatment, you can minimize this suffering and give your cat years of quality living with hyperthyroidism.

How serious is hyperthyroidism in cats?

Hyperthyroidism in cats may be common, but it’s a serious condition. If your cat has hyperthyroidism, seeking treatment as soon as possible will help you minimize their sigs and provide them with a happier life. Left untreated, hyperthyroidism can be fatal to cats, so you should always consult a vet if you notice signs of hyperthyroidism.

What is the best food for a cat with hyperthyroidism?

Some research shows that cats with hyperthyroidism may benefit from a low-iodine diet. If you’re interested in learning what a low-iodine diet can do for your cat, contact your vet for nutrition advice.

Final Notes

An estimated 1 in 10 senior cats will suffer from hyperthyroidism. As a cat owner, it’s important to stay well aware of signs that your cat may have hyperthyroidism. These include behaviors like weight loss, despite an increase in appetite, increased thirst and frequent urination, and a greasy and matted looking coat.

If you suspect that your cat may have developed feline hyperthyroidism, it’s time to speak to a vet. They can work with you to find the right treatment option. Dutch members get unlimited access to licensed veterinarians from the comfort of their own homes. Plus, all Dutch members get free shipping on all Dutch online pet pharmacy orders. Join Dutch for these perks and more.