Hyperthyroidism in Cats
Written by Small Door's medical experts
Hyperthyroidism is an endocrine (hormonal) disorder that occurs most commonly in older cats. Cats with hyperthyroidism produce excessive amounts of thyroid hormones, which affects their metabolic rate and can cause potentially dangerous side effects.
In This Article
Endocrine disorders like hyperthyroidism can lead to severe problems, like congestive heart failure. Being aware of the signs and symptoms of hyperthyroidism will help getting an accurate diagnosis as soon as possible, and understanding the treatment and management protocols will better prepare you for managing it.
Symptoms of hyperthyroidism in cats are directly related to increased metabolic rates. These symptoms include:
Enlarged thyroid gland
More poop than usual
Cardiomegaly (enlarged heart)
Increased heart rate
Congestive heart failure
Increased metabolic rates speed up your cat’s bodily processes, which means that all their systems are essentially working overtime and can lead to physical changes like weight loss, changes in their gastrointestinal system, and even cardiovascular changes. Some of these changes are easier to observe than others.
Weight loss, for instance, can be seen and felt, but you might not notice that your cat is experiencing higher volumes of urine and poop unless you scoop the litter box on a daily basis. Weight loss in cats should always be taken seriously, as it is a noticeable sign of health problems.
Symptoms of hyperthyroidism worsen over time. If left untreated, you may notice more serious signs as your cat’s condition progresses, such as sudden blindness caused by high blood pressure induced retinal detachment and congestive heart failure.
Cats develop hyperthyroidism most commonly in the middle to old age. In most cases, benign growths on the thyroid gland or glands, which enlarges the gland and stimulates increased production of thyroid hormones, causes hyperthyroidism.
Benign thyroid adenoma (growth)
Over 70% of cases of hyperthyroidism in cats involves the enlargement of both thyroid glands. In most cases, these growths are benign, but in rare cases (1-2% of cases), they could be caused by thyroid carcinoma. Both benign and cancerous growths cause increased production of thyroid hormones, which elevates hormone levels in their bodies and increases their metabolism.
Hyperthyroidism in cats is diagnosed by measuring the level of thyroid hormones in the cat’s blood serum. If your veterinarian suspects that hyperthyroidism could be a cause of your cat’s symptoms, he or she will take a blood sample from your cat to measure the high basal serum total thyroid hormone concentration. Levels outside normal limits confirm the diagnosis.
Sometimes, cats in the early stages of hyperthyroidism or with concurrent illnesses that suppress high total T4 concentrations may present with normal thyroid levels. These cats may need additional diagnostic tests, like a free T4 concentration, to confirm hyperthyroidism as well as any other conditions.
Your veterinarian will also look for problems potentially caused by hyperthyroidism. Heart problems can arise in advanced stages of the disease, and your veterinarian may recommend additional tests, like ultrasounds and echocardiography, to determine the seriousness of the heart disease.
Liver and kidney disease are also common in older cats, and veterinarians often recommend tests to measure white blood cell count, potassium, liver and kidney function, and blood pressure. Benign growths cause most cases of hyperthyroidism, but if your veterinarian suspects thyroid cancer, additional testing like a biopsy or fine needle aspirate to determine the cause of the growth may be recommended.
Several treatment options are available for hyperthyroidism, including medications, surgery, radiation, and dietary changes. The best treatment plan will depend on your cat’s health, your budget, and treatment availability.
Medication therapy for hyperthyroidism controls thyroid levels with medication. Methimazole is the most common drug used and comes in a pill or a compounded paste form. Your veterinarian will need to track your cat’s thyroid levels to determine the best dosage and to make adjustments over time. Your vet will also monitor your cat for signs of medication side effects, which can include low white blood cell counts, low platelet counts, and liver problems.
Surgery to remove one or both thyroid glands will resolve high thyroid levels. However, cats with both glands surgically removed will then be considered hypothyroid and will require thyroxine supplementation to keep their thyroid levels within a normal range.
Iodine radiation therapy is another possibility, as long as the cat’s kidneys are functioning normally. However, this therapy is one of the more expensive options and is not available in all hospitals.
Some cats respond well to a change in diet. Prescription diets that restrict iodine levels, like Hills y/d Feline Thyroid Health, provide an iodine deficient diet that reduces thyroid hormone levels, and ideal for cats not eligible for other treatments.
However, owners must be cautious not to allow cats access to table scraps, treats, or other food, as even trace amounts of iodine can make the diet ineffective, and dietary changes may not work for cats with severe cases of hyperthyroidism.
Is There a Cure for Hyperthyroidism?
Surgically removing affected thyroid glands will cure hyperthyroidism in cats. However, surgery is not always an option. Other treatments will control hyperthyroidism but not cure it.
Is Hyperthyroidism Contagious for Humans or Other Pets?
Hyperthyroidism is not a contagious disease and cannot be spread to humans or other pets.
What Is the Cost for Treating Hyperthyroidism?
The cost of treating hyperthyroidism in cats will vary depending on the treatment option chosen, differing rates between veterinary practices, and complications that may arise following treatment. Talk with your veterinarian for the best way to get an accurate estimate for the cost of treating your cat’s hyperthyroidism and be sure to communicate any financial concerns you may have.
Managing a hyperthyroid cat will require different protocols depending on the treatment option. Medical management, for instance, will need regular monitoring every few months with your veterinarian to correct the dosage. Recovering from surgery, on the other hand, may require a few days of rest plus a possible prescription for thyroxine, and iodine radiation necessitates a hospital stay until the radiation has been fully excreted from your cat’s body.
Dietary treatment plans will require the most management, as they need the most vigilance. Any other source of food, including predation, can affect the treatment, and owners must take great care to prevent their cats from accessing alternate food sources. Cats fed a prescription diet will still require veterinary monitoring to ensure the treatment is working.
Hyperthyroidism in cats cannot be prevented. However, regular wellness exams can help veterinarians catch hyperthyroidism before the disease progresses, reducing the chances of your cat eventually developing heart disease or retinal detachment.
Is There a Vaccine for Hyperthyroidism?
Hyperthyroidism is not a viral condition. There is no vaccine for hyperthyroidism in cats.
Hyperthyroidism in cats is a disorder where excessive amounts of thyroid hormones are produced, increasing their metabolic rate. Common symptoms include weight loss, increased appetite and thirst, and increased urination. If untreated, hyperthyroidism can have serious effects, so it’s important to take your cat to the vet as soon as you notice symptoms. While hyperthyroidism cannot be prevented, it is a manageable condition. With monitoring and veterinary care, cats with hyperthyroidism can live healthy, active lives.