Hyperthyroidism: What Cat Owners Need to Know
What is hyperthyroidism in cats?
Hyperthyroidism in cats is similar to hyperthyroidism in humans. It is an endocrine disease because it affects the organs that make and secrete hormones. The significant difference between human and feline hyperthyroidism is the available treatment options.
The thyroid gland is found in the necks of people and cats alike. It is often described as “butterfly-shaped” because it has a lobe on each side of it. The thyroid gland is super important because it regulates your body’s metabolism and your metabolism controls a lot of critical processes in your body. So it’s pretty important that it functions properly.
In hyperthyroidism for cats, the thyroid gland is overactive and produces too many thyroid hormones, known as T3 and T4. A hyperthyroid gland works at double or triple the speed of a normal thyroid.
In almost 99% of feline hyperthyroidism cases, the disease is caused by a non-cancerous tumor on the thyroid gland called an adenoma. These tumors are benign and rarely spread, but they cause an abnormally high metabolic rate and negatively affect almost all of your pet’s organs. The other 1% of hyperthyroidism in cats is rare and caused by malignant tumors known as thyroid adenocarcinomas.[1]
The most significant factors that affect the future of your cat’s health are early detection and how well your pet responds to treatment. Luckily, the prognosis for hyperthyroidism in cats is ultimately good!
Is hyperthyroidism common in cats?
Hyperthyroidism occurs in about 10 percent of cats over the age of 10 and is the most common endocrine disease in cats. The average age of affected cats is 12 and only 5% of hyperthyroid cats are younger than 10.[2]
As of now, no known breed has a higher risk of developing feline hyperthyroidism. But Siamese, Burmese, Persian, Abyssinian, and Himalayan breeds appear to have a somewhat decreased incidence of hyperthyroidism compared to others.[3]
Causes for Hyperthyroidism in Cats
It is still unknown what causes hyperthyroidism in cats, but we do suspect dietary deficiencies or excesses are at the root of the problem. Research shows that cats who consume large amounts of commercial fish-flavored food are more likely to develop the disease than cats with a cleaner, more holistic diet.[4]
How do I know if my cat has hyperthyroidism?
Across the board, veterinarians agree the most common sign to look for with hyperthyroidism in cats is weight loss despite an increased appetite.[5] This symptom shows in up to 98 percent of affected cats, so it’s the one that most people notice first.[4] Weight loss is due to the increased metabolism associated with hyperthyroidism in cats.
Other common signs include:
Rapid heart rate
Vomiting or diarrhea
Hyperactivity
Drinking and urinating more than usual
Unkempt hair coat
Increased crying or irritability
With recent advancements in veterinary medicine and more knowledge about feline hyperthyroidism, routine hyperthyroid screenings are now regular practice for middle-aged to older cats. Because cat hyperthyroidism is so common, many veterinarians diagnose it earlier than ever before.
In most cases, symptoms of hyperthyroidism in cats are easy to miss early on because it develops so gradually, and even a small percentage of hyperthyroid cats may not exhibit any obvious disease signs at all.[4]
But if your cat is displaying more than one of the above signs, reach out to your veterinarian to schedule a thyroid test ASAP. It’s crucial to catch the disease early to help mitigate the potentially fatal effects of late-stage hyperthyroidism.
Symptoms of Late Stage Hyperthyroidism in Cats
Thyroid hormones affect nearly all of the organs in the body and because of their pervasive nature, thyroid disease often causes secondary problems. If an adequate diagnosis isn’t performed early enough, serious issues arise.
About 25% of cats with hyperthyroidism develop high blood pressure (hypertension).[6] Fortunately, after hyperthyroidism is successfully treated, high blood pressure will often resolve and may not require further treatment.
But it is known that a severe problem in cats with chronic high blood pressure is sudden blindness. In these dire cases, the animal’s blood is pumping so hard and fast it causes a cat’s retina to detach from the back of the eye. If this detachment isn’t treated right away, permanent blindness can occur.
High blood pressure has the potential to cause damage to other organs as well, including the heart, brain, and kidneys. It is common to find that after treating hyperthyroidism in your cat, hidden kidney failure will be uncovered and require separate treatment.
Another common complication of hyperthyroidism in cats is heart disease. A specific type of heart disease associated with hyperthyroidism is called thyrotoxic cardiomyopathy. In this type of cardiomyopathy, the heart grows bigger to meet the increased demand for metabolic processes caused by hyperthyroidism. This heart enlargement can also cause heart murmurs and, in some cases, even heart failure.
The good news is that cardiomyopathy and hypertension are potentially reversible with appropriate treatment and an early diagnosis. While some cats with hyperthyroidism may need further treatment to control secondary heart disease, once the underlying hyperthyroidism is managed successfully, the cardiac abnormalities improve or may resolve completely.[7]
How to Diagnose Hyperthyroidism in Cats
If you suspect your cat has hyperthyroidism based on what we’ve described above, please contact your veterinarian. Your vet will ask about symptoms and behaviors your pet is showing and feel your cat’s neck, looking for the tell-tale sign of an enlarged gland. The doctor will also check your cat’s heart rate and blood pressure to see if the heart is performing as it should.
Before choosing a treatment, your vet may require an ultrasound of the heart (echocardiography). This will be determined based on your pet’s situation but is highly recommended if there is any chance of cardiomyopathy. Before surgery or radioactive iodine treatment, thyroid scintigraphy may also be recommended to see if the heart has enlarged.[8]
To confirm a diagnosis, your vet performs blood tests. These tests measure and check the hormones in your cat’s body that cause hyperthyroidism. With these tests combined, your vet is gaining a better understanding and complete look into your cat’s health - the most common tests for hyperthyroidism in cats are:
Complete Blood Count (CBC)
Blood Chemistry Panel
Thyroid Hormone Analysis
Urinalysis
In most cases, the above tests confirm if your cat suffers from hyperthyroidism. If a doctor sees an elevated level of the T4 hormone, they make a diagnosis.
But, in some frustrating cases, up to 10 percent of hyperthyroid cats may have normal T4 levels, and a diagnosis for these cats requires additional specialized testing.[9]
If your pet’s first panel of tests is not showing anything off with T4 levels, there are laboratories that offer a more comprehensive panel. This test is called the Feline Thyroid Panel and measures more than just T4. It also checks T3, free T4, and TSH - other hormones produced by the thyroid gland. A deeper look into these hormones is needed when treating a feline with many health problems, possibly more than just hyperthyroidism.
How to Treat Hyperthyroidism in Cats
This is a wide-known fact: untreated hyperthyroidism in cats is almost 100 percent fatal.[5] But we are thankful to know that since fewer than 2% of cats with hyperthyroidism have cancerous tumors on the thyroid gland, treatment is usually very successful.[8] Remember, almost 99% of thyroid tumors are benign!
The main goal of hyperthyroidism treatment is to lower the levels of thyroid hormones in your cat. You and your veterinarian choose the best choice for your cat and situation because many factors affect your decision.
There are currently three safe and available medical treatment options for feline hyperthyroidism:
Radioactive Iodine Therapy (I-131)
The most effective way to treat hyperthyroidism in cats is I-131 therapy, and it is considered a cure for hyperthyroidism in cats.
Cornell University research shows that in about 95% of all hyperthyroid cases, radioactive iodine therapy cures hyperthyroidism in cats within three months of therapy.[7] And the majority of cats treated with radioactive iodine most often have normal hormone levels within one to two weeks of treatment.
This therapy uses injections of iodine that target abnormal thyroid tissues and avoids harming other organs. Because it is so effective, it removes the need for lifelong doses of medicine.
You can generally expect your cat to be in the hospital for one or two weeks at a veterinary hospital licensed to administer I-131 therapy. The process does not require anesthesia. Your cat may need to take methimazole for a month before radioactive iodine therapy to help control existing symptoms before the procedure.
Your cat will need an outpatient diagnostic imaging center like Sage Veterinary in Round Rock, TX or Sandy, UT to receive this treatment. We are licensed to perform I-131 therapy for cats.
Medication
There is only one medication approved by the FDA to treat hyperthyroidism in cats. It is called methimazole. This highly-effective medication is only available with a veterinarian’s prescription.
Methimazole is safe and effective in cats when used according to the directions on the label. The medication can be given orally or applied to your cat’s skin. There are varying dosages based on your vet’s diagnosis and recommendation.[4]
To control hyperthyroidism with medication, your cat takes daily pills and this is a lifelong treatment. You should also expect regular blood work panels and follow-ups. Routine monitoring will help your vet understand how well your feline friend is recovering.
Surgery
A thyroid surgery is called a thyroidectomy. Although this surgery was once the standard treatment for hyperthyroidism in cats, it isn’t used as frequently now. It has since been replaced with radioactive iodine therapy.
Where surgery is the only option, it has a good success rate. But not all cats are the best candidates for surgery. If your vet has concerns about your cat’s age, heart, kidney, or other complications, surgery and anesthesia are not recommended. There are also rare cases where cancer may have spread too far for surgery to be the right action plan.
The advantages of surgery are it can be a permanent cure in most cats and there is no need for long-term medication. Surgery is more invasive than other treatments, so it is usually not the best option for treating hyperthyroidism because we have better options available.
Prescription Diet for Cats with Hyperthyroidism
You will discuss your options with your vet, however, no matter which method you choose, diet is an essential part of all of them. Changing your cat’s diet to deal with disease is part of a holistic approach to healthier living for your pet.
Because thyroid glands need iodine from food to make hormones, a diet with very low levels of iodine has positive effects. When diseased thyroid glands don’t get iodine, they don’t make as many thyroid hormones, and the thyroid will stop overproducing.
There is one prescription diet available used to control hyperthyroidism in some cats, made by Hill’s Pet Nutrition. The food is not medicated or iodine-free but made with a precisely controlled iodine content of 0.2 ppm - a minimal amount.[3] For best results, strict adherence to the diet is mandatory - this means no treats or other medications, including herbal medicines.
Changing your cat’s food might be the best option if other treatment options aren’t available. Research into this potential treatment option is ongoing. Discuss these issues with your veterinarian when considering a low-iodine diet as a treatment for hyperthyroidism in cats.[7]
Which treatment is the best for hyperthyroidism in cats?
When available, I-131 is the preferred treatment by doctors and patients. Because the chance of recurrent hyperthyroidism is lower in I-131 than in other treatments, the success rates are simply higher.
Surgical patients may become hyperthyroid again if abnormal cells were missed in surgery or if new abnormal cells develop. If medication stops, hyperthyroidism will definitely return. Cats exclusively fed the prescription diet will remain normal, but if the diet is stopped, they will once again become hyperthyroid.
There are pros and cons for each option. Ultimately, your choice for your cat depends on the specific situation. A pet’s overall health, the owner’s finances, and the ability to care for their pet all factor into how treatment happens. At Sage Veterinary Imaging, we help you make that decision and walk you through each step of the process.
Sage Veterinary Imaging in Sandy, Utah
Sage Veterinary Imaging in Texas and Utah Treats Hyperthyroidism in Cats
At Sage Veterinary Imaging, we perform diagnostic thyroid scintigraphy and treat feline hyperthyroidism with I-131. A licensed and board-certified radiologist performs all scintigraphy and I-131 injections in our clinics.
Since 2015, Sage Veterinary Imaging has been operating in Round Rock, Texas, and in 2022 opened a new state-of-the-art imaging center in Sandy, Utah. Advanced imaging is the foundation of veterinary medicine and the key to exceptional treatment outcomes. We help you get answers and an accurate diagnosis that leads to the most effective treatment for your best animal friend.
Look no further when you need the latest imaging technology and a board-certified radiologist. Sage Veterinary Imaging provides same-day appointments and outpatient efficiency. Combined with the highest quality diagnostic images available, you get the best treatment and the right information. Our mission is to deliver world-class outpatient veterinary diagnostic imaging to pets using cutting-edge MRI, CT, x-ray, and ultrasound technology.
References:
https://www.fda.gov/animal-veterinary/animal-health-literacy/hyperthyroidism-cats-theres-fda-approved-drug-treat-it
https://catvets.com/public/PDFs/ClientBrochures/Hyperthyroidism-WebView.pdf
https://vcahospitals.com/know-your-pet/hyperthyroidism-in-cat
https://www.fda.gov/animal-veterinary/animal-health-literacy/hyperthyroidism-cats-theres-fda-approved-drug-treat-it
https://vcahospitals.com/know-your-pet/hyperthyroidism-in-cats
https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/hyperthyroidism-cats
https://blog.petwellbeing.com/blog/cats/holistic-teatments-for-hyperthyroidism-in-cats
https://vcahospitals.com/know-your-pet/hyperthyroidism-in-cats
