- Not a substitute for professional veterinary help.
You want your cat to feel happy and healthy long into their golden years. We want that for your cat, too. That’s why we wanted to cover an important disorder that cat owners need to be aware of—hyperthyroidism in cats.
Hyperthyroidism is an endocrine disorder that affects a significant portion of the feline population. Cats are increasingly at risk as they age.
But what is hyperthyroidism in cats? What are the symptoms? Most importantly, if your cat has hyperthyroidism, how can you treat the disorder? We’ve answered that and more to ensure your cat goes on to live a long, healthy life.
Before we dive into how to spot hyperthyroidism in your cat (and, more importantly, how to treat it), let’s quickly cover what hyperthyroidism is.
“Feline Hyperthyroidism is one of the most common endocrine diseases in cats, and affects over 10 percent of cats 10 years or older in the United States,” says Turnera Croom, DVM, a veterinarian with a mobile veterinary practice in Southwest Michigan.
When it comes to what causes hyperthyroidism in cats, there are no definitive answers. “Unfortunately, we do not completely understand the origin of hyperthyroidism in cats; it is most likely that there are multiple influencing factors,” says Robin Downing, DVM, veterinarian and hospital director of The Downing Center for Animal Pain Management in Windsor, CO. “That said, there has been a linkage described between certain fire retardants used in carpet and upholstery and an increased risk of hyperthyroidism. Another theory is that BPA, which is often used to line metal food cans, may serve as an endocrine disruptor and have a toxic effect on the thyroid gland.”
Diet may also play a role. “We know that many, if not most, cat foods (especially those with fish as the primary protein source) have very high levels of iodine,” says Dr. Downing. “Increased intake of iodine over a lifetime may contribute to the development of hyperthyroidism in certain [cats].”
Initially, hyperthyroidism in cats can be hard to spot. Symptoms may be mild at the beginning of the disorder, and certain symptoms can mimic other issues. For example, vomiting can be a sign of hyperthyroidism in cats—but it can also be a sign of indigestion or cat hairballs. That’s why it’s so important to know exactly what to look out for. If you have hyperthyroidism symptoms on your radar, you can keep an eye on your cat—and get them the proper veterinary attention as soon as they start exhibiting potential signs of hyperthyroidism.
According to PetMD, symptoms of hyperthyroidism in cats include:
- Increased appetite
- Weight loss—despite increased food intake (“A cat with hyperthyroid will eat voraciously, but will still lose weight over time,” Dr. Croom explains.)
- Increased thirst and water intake
- Increased urination
- Restlessness (“A common client complaint is that these cats [with hyperthyroidism] are restless at night, wandering the house and vocalizing,” Dr. Downing adds.)
- An unkempt or greasy coat
Hyperthyroidism can cause serious health issues for your cat. “If left untreated, a kitty with hyperthyroidism will continuously lose weight from the circulating thyroid hormones,” says Dr. Croom. “[They] will routinely have increased body temperature, heart and respiration rates, and hyperactivity, which could lead to hypertension.”
And hypertension brings its own set of challenges. “Hypertension can be so severe that they actually detach their retinas and become blind,” says Dr. Downing. “Hypertension can [also], in turn, lead to kidney disease and pathologic changes in the heart muscle.”
Bottom line: if you suspect your cat might be struggling with hyperthyroidism or they’re exhibiting even minor symptoms, it’s important to get them to the vet and on a proper treatment protocol ASAP.
While your vet will likely want to perform a physical examination to look for signs of hyperthyroidism (like a rapid heartbeat or enlarged thyroid gland), the only way to diagnose hyperthyroidism in cats is through a blood test that measures the level of thyroid hormones (T4) in your cat’s blood.
If the test returns with elevated T4 levels, your cat has hyperthyroidism. If your cat’s thyroid hormone levels are on the border between normal and high, your vet may order additional tests before offering a diagnosis of hyperthyroidism.
While the initial T4 test will be used to diagnose your cat with hyperthyroidism, you’ll also need to get periodic blood tests to check their thyroid hormone levels and adjust treatment as necessary.
If your cat has hyperthyroidism, it’s important to get treatment as soon as possible. Here’s what that treatment will likely look like.
Medication is an extremely effective treatment for hyperthyroidism in humans—and it also happens to be an extremely effective treatment for hyperthyroidism in cats. “Oral medication—methimazole—is [a] treatment option,” says Dr. Downing. “[It] must be given every single day, and it is a lifetime medication in these cats.”
However, while Methimazole can be extremely effective at regulating thyroid function, it’s not without its drawbacks. “Unfortunately, the medication can cause side effects of its own including incontinence, vomiting, lethargy, and liver issues,” says Dr. Downing. “Rarely it can cause severe facial itching and self-trauma.”
Before you start medication treatment, talk to your vet and make sure it’s the best option for your cat. And, if you do move forward with medication, be sure to schedule regular check-ups to allow your vet to monitor your cat’s thyroid hormone levels (which will allow them to adjust the dosage as needed).
As mentioned earlier, an overabundance of iodine in their diet may cause hyperthyroidism in cats—but interestingly, iodine is also a go-to for treating the disorder. “Just like in human medicine, radioactive iodine therapy (I-131) is an option [for treating hyperthyroidism in cats],” says Dr. Downing. “This compound is given by injection, [where it then] concentrates in the thyroid gland and destroys the offending tissue.”
While parts of the treatment process can be extreme (“Cats must be kept in the licensed facility where the I-131 is administered until the level of radioactivity of their urine and stool falls to an acceptable level,” says Dr. Downing), radioactive iodine treatment is by far the most effective for hyperthyroidism in cats. According to the Cornell University College of Veterinary Medicine, the treatment cures 95 percent of hyperthyroidism within three months. “It is considered a definitive cure, although some cats will then require supplementation with thyroid hormone,” says Dr. Downing.
Surgical removal of the thyroid gland can also be an option for treating hyperthyroidism in cats, but it’s not the ideal option. Surgery and anesthesia can cause serious health complications, especially in older cats, who are most likely to struggle with hyperthyroidism.
Before you decide to move forward with thyroid surgery, make sure to explore any and all alternative treatment options with your vet.
Changes to the cat’s diet and environment
While you’ll definitely want to get the right medical treatment for hyperthyroidism in cats, making changes to your cat’s diet and environment may also help. “As a holistic veterinarian, I typically guide my clients toward treatments such as adjusting kitty’s diet to eliminate fish products, acupuncture, and nutraceuticals,” Dr. Croom says.
Dr. Croom also recommends keeping the home free of polybrominated diphenyl ethers (or “PBDEs”), which are used as a fire retardant and have been linked to an increased risk of hyperthyroidism in cats.
Your vet might also be able to prescribe food specifically formulated to treat hyperthyroidism in cats. “There is now a therapeutic nutritional option available that, if fed exclusively, will help cats achieve remission from their hyperthyroidism,” says Dr. Downing. “It must be the ONLY food fed (no treats or human food), and it works by very precisely controlling the amount of iodine the cats ingests…It is a non-invasive, non-surgical way to achieve remission, and is generally a well-accepted food.”
Hyperthyroidism is a serious condition—and, without proper treatment, the disorder can adversely affect your cat’s lifespan. “Left untreated, hyperthyroid cats will have a shortened lifespan,” says Dr. Downing.
But there’s good news! While hyperthyroidism is a serious condition, it’s also an extremely manageable one. With proper treatment, your cat’s life expectancy (and quality of life!) likely won’t be affected by the disorder at all, Dr. Downing says.
The earlier your spot hyperthyroidism in your cat, the earlier you can get them treatment and the better their prognosis, both for overall quality of life and life expectancy.
Hyperthyroidism in cats is an extremely common endocrine disorder—but it’s also an extremely treatable one. Now that you know the ins and outs of feline hyperthyroidism (from how it’s diagnosed to the best treatment options available), you have everything you need to spot hyperthyroidism and get your cat the treatment they need to live a long and healthy life.