Hyperthyroidism is one of the most common health problems in older cats. It happens when a cat’s thyroid glands make too much thyroid hormone, resulting in your cat’s body working too fast.
The good news is that hyperthyroidism can have a positive prognosis. Many cats can go on to have a good quality of life for many years after their diagnosis.
What Is Hyperthyroidism in Cats?
To understand hyperthyroidism, you need to know what the thyroid glands actually do. There are two small thyroid glands located in the neck that produce T3 and T4 hormones. These hormones affect a bunch of different things in the body, including the heart, digestive system, and metabolism.
Cats with hyperthyroidism have an enlarged thyroid gland that produces excessive amounts of thyroid hormone. Since these hormones regulate metabolism, too much makes your cat's body use energy more quickly.
Hyperthyroidism can affect male and female cats of any breed, but it most often occurs in middle-aged and older felines. Research searching for possible links between hyperthyroidism and diet or chemicals in the environment is ongoing, but so far a specific cause is unknown.
Although the root cause of feline hyperthyroidism is unclear, in most cases, an adenoma (a benign tumor) causes the enlargement. However, thyroid cancer is also a possibility, although this is not as common in cats.
Common Signs of Feline Hyperthyroidism
The signs of hyperthyroidism in cats can be easy to miss at first. Some pet parents may simply think their cat is getting older. However, changes in appetite, weight, thirst, or behavior can be important clues.
Therefore, if you ever notice any of these symptoms in your cat, don’t ignore them. The earlier you see a vet, the better. A speedier hyperthyroidism diagnosis means treatment begins sooner, improving the odds of your cat avoiding serious complications.
Weight Loss
One of the most common signs of hyperthyroidism is weight loss even though your cat is eating normally or eating more than usual. Since your cat’s metabolism is working faster, they burn more energy.
Increased Appetite
Your cat might seem hungry all of the time, and yet, they continue to lose weight. Your cat may beg for food, scarf down meals, or act as though they’re never full.
Increased Thirst and Urination
If your cat drinks more water and urinates more often, it could be a sign of hyperthyroidism. However, these changes can also occur with other illnesses, such as kidney disease or diabetes, which is why you should always address the issue.
Vomiting or Diarrhea
A cat with hyperthyroidism may vomit more often or develop diarrhea. You may also notice that your cat produces larger amounts of stool.
Restlessness or Hyperactivity
Your cat’s behavior is another good indicator that something isn’t quite right. Hyperthyroidism can make your cat unusually active, restless, nervous, or vocal. For example, your normally calm cat is now pacing around the house, being more demanding, or meowing constantly.
Changes in the Coat
Any changes in your cat’s coat are also worth paying attention to. When things aren’t quite right, cats might not self-groom as usual, leading to greasy or matted fur.
Fast Heart Rate or Breathing Problems
Excessive amounts of thyroid hormone can affect the heart. A veterinarian may notice a very fast heart rate, a heart murmur, or other heart changes. Some cats might also have trouble breathing or have high blood pressure.
Keep in mind that not every cat with hyperthyroidism will show signs of all these issues. Some might even show opposite signs, like appetite loss or fatigue, especially in the later stages of the disease.
So don’t wait until you notice more than one symptom. Even one clue should be enough to get you on the phone with the vet.
How Do Vets Diagnose Hyperthyroidism?
If your veterinarian suspects hyperthyroidism, they’ll start with a physical exam and ask about changes you have noticed at home. The vet might feel your cat's neck to check for an enlarged thyroid gland and check heart rate, blood pressure, weight, and overall condition.
A blood test is usually what confirms the diagnosis. One important test measures the amount of T4 in the blood to look for elevated levels.
Sometimes a cat shows signs of hyperthyroidism, but a T4 test falls within the normal range. This can happen, especially early in the disease. In these cases, the veterinarian may recommend another thyroid test or additional testing. Also, they’ll look at your cat’s entire health picture, history, and consider clinical signs.
Your veterinarian may also recommend blood work and a urine test to assess kidney function and other organs. This is important because hyperthyroidism can occur at the same time as other health problems. Treating hyperthyroidism can also reveal kidney disease that was hidden by the effects of the overactive thyroid.
What Is the Treatment for Hyperthyroidism in Cats?
There are four main treatment options for feline hyperthyroidism:
- Radioactive iodine therapy
- Anti-thyroid medication
- Surgery
- A prescription iodine-restricted diet
The best treatment choice depends on your cat's health, age, and other medical conditions. Also, your vet will consider how well your cat takes medication and your family's circumstances. It’s best to discuss all options with your vet to determine which one is the best fit for your feline friend.
Radioactive Iodine Therapy
Radioactive iodine, also called radioiodine or I-131 therapy, is often the preferred treatment when it’s available. It targets the overactive thyroid tissue while causing little damage to other parts of the body.
One major advantage is that radioactive iodine treatment can reverse many cases of hyperthyroidism within several months. Your vet will recommend a facility equipped to handle radioactive materials, and your cat will likely need to stay there for a designated period after treatment due to radiation safety rules.
Anti-Thyroid Medication
Medications such as methimazole help lower thyroid hormone produced by the thyroid gland. However, this only controls the disease; it does not remove the underlying thyroid growth. Therefore, if this is your only treatment option, your cat will most likely remain on the medication for the rest of their life.
Consequently, your cat will need regular blood tests to make sure everything’s working properly and to look for potential side effects. Side effects could include vomiting, appetite loss, tiredness, and skin problems.
In rare cases, your cat may experience liver or blood issues. Always contact your vet immediately if your pet develops any strange symptoms when they’re on medication.
Surgery
Surgery to remove the affected gland is another option and can offer a long-term or permanent cure for cats with hyperthyroidism. However, it requires general anesthesia, which can be riskier for older cats or those with heart, kidney, or other health problems.
Other surgical risks include trouble with the parathyroid glands. These glands help regulate calcium levels in the body. Therefore, do your research and make sure to find a veterinarian experienced with the procedure.
Prescription Iodine-Restricted Diet
A special prescription diet with very low iodine can help control hyperthyroidism by reducing hormone production. However, for it to work, you need to feed your cat this special diet exclusively and for life. If your cat eats treats, table food, pet food, or even prey, they could get iodine, which can make the diet less effective.
Why Treatment and Monitoring Matter
Untreated hyperthyroidism could lead to extra stress on your cat’s heart and other organs, and increase the risk of heart disease and high blood pressure. Your cat may also have kidney disease at the same time that goes unnoticed because of the overactive thyroid.
After treatment begins, your veterinarian will monitor your cat. Monitoring helps veterinarians identify possible problems and adjust treatment as needed. They’ll check kidney function, blood pressure, and run blood tests to show whether thyroid hormone levels are returning to a healthy range.
In some cats, treatment can cause thyroid hormone levels to become too low. This condition is called hypothyroidism, which can cause tiredness, weight gain, and an unhealthy coat.
Recognizing Hyperthyroidism in Cats
Hyperthyroidism is common in older cats, but it’s also treatable, especially when you catch it early. Therefore, know the signs, and don’t assume changes are simply because your cat is aging.
Seek veterinary care right away to get your cat on the most appropriate treatment plan. Proper diagnosis, treatment, and follow-up care can give many cats with hyperthyroidism a chance to live comfortable, active lives.
Check out more of the Neater Pets blog for other helpful pet-parenting tips, tricks, and tidbits.