What are the signs of hyperthyroidism in cats?

Feline hyperthyroidism is a common condition in senior cats where the thyroid glands are overactive and produce excessive amounts of thyroid hormones. Early clinical signs can be subtle, but it’s important for cat owners to recognize these signs of illness in their older pets. Read on to learn:

• What is hyperthyroidism, and how does it affect cats?
• What are the symptoms of hyperthyroidism in cats?
• How is feline hyperthyroidism diagnosed and treated?
• What should I do if I think my cat has hyperthyroidism?

Weight loss is a common symptom of hyperthyroidism and not a normal sign of aging in cats. Other symptoms, like appetite changes, increased thirst, and changes to the skin and coat, are common in cats with hyperthyroidism. With proper treatment and control of hyperthyroidism, your affected cat can live a normal lifespan and have a good quality of life.

Hyperthyroidism is the overactivity of the thyroid glands, leading to the overproduction of thyroid hormones. Cats have two thyroid glands located in the neck that release hormones to control bodily processes, such as metabolism and the absorption of calcium. When thyroid hormone levels are too high, these processes can be affected. Hyperthyroidism is a common disease in cats and the most common endocrine disease, which are disorders that affect the endocrine system, in cats over the age of ten.

Overproduction of thyroid hormones affects multiple organs throughout the body, resulting in a variety of symptoms. Common signs of hyperthyroidism in cats include:

• Weight loss
• Increased appetite
• Excessive thirst
• Excessive or frequent urination
• Increased energy levels or restlessness
• Increased heart rate
• Vomiting or diarrhea
• Unkempt, matted, or greasy coat
• Dry skin
• House soiling
• Aggressive behaviors

Hyperthyroidism results in an increase in metabolic rate, which is the amount of energy a body uses up, and this typically leads to weight loss in cats despite a good appetite. As the disease progresses, vomiting and diarrhea usually develop, primarily because the cat is eating so much, and litter box accidents are common. As the metabolic rate continues to go up, increased energy can also lead to restlessness, aggressive lashing out, pacing, increased vocalization, and irritability.

Early symptoms of hyperthyroidism are mild, and the disease may progress over many months or years, making the signs easy to miss. “Since hyperthyroid cats usually have lots of energy and eat well, they  don’t seem sick,” says Dr. Jo Myers, a veterinarian on the Vetster platform. “As a result, it’s easy to overlook early signs or attribute them to aging. Getting skinny, however, is not a normal part of getting older for cats.”

Hyperthyroidism is most common in cats over the age of ten. Advanced age is the biggest risk factor for the development of hyperthyroidism in cats. While indoor cats seem to have a slightly higher risk of developing the condition, veterinarians have yet to identify a specific cause of hyperthyroidism related to being indoors.

Cats with hyperthyroidism often have an elevated heart rate and blood pressure as well as an enlarged thyroid gland. A diagnosis is made using a blood test that measures levels of hormones related to thyroid activity. Hyperthyroidism, like many other hormonal disorders, doesn’t show up on routine blood work. The specific test used to diagnose hyperthyroidism is most commonly performed during wellness screens on senior cats or when hyperthyroidism is suspected.

A definitive diagnosis is needed to treat hyperthyroidism. Cats with hyperthyroidism need proper treatment from a veterinarian to protect their quality of life and to prevent complications such as heart failure. Treatment options for feline hyperthyroidism include:

• Topical or oral medication
• Radioactive iodine therapy
• Surgical treatment

Radioactive iodine therapy is the most effective treatment of hyperthyroidism in cats, but it isn’t always practical or accessible. Only certain facilities are certified to handle the radioactive iodine, and treatment can be very expensive. Afterwards, cats need to be kept isolated for several days in a hospital. Radioactive iodine therapy often cures hyperthyroidism, and once a cat’s hyperthyroidism is cured, no other treatments are necessary.

When radioactive iodine treatment isn’t an option, medication is the most common alternative. Given daily as an oral pill or a topical compound put on the ear, medication can manage the condition. Once your cat is prescribed medication for hyperthyroidism, they must continue taking the medication for the duration of their life, and regular blood tests and monitoring are also required to ensure your cat’s thyroid hormone levels remain normal.

If thyroid tumors are causing elevated levels of thyroid hormone, surgery might be an option. Surgery is typically less expensive than radioactive iodine treatment and medications in the long run. However, surgical treatment has its own set of advantages and disadvantages, including the possibility that thyroid hormones drop too much afterwards, resulting in hypothyroidism, and cats that have undergone thyroid surgery may still need additional surgery or medication in the future.

Can hyperthyroidism be cured?

Radioactive iodine therapy is the most effective treatment and is most likely to cure hyperthyroidism, though it’s not always available and can be expensive. While surgical treatment has the potential to be curative, additional treatment is often necessary. Cats treated with thyroid medications are not “cured” but can have very well-managed hyperthyroidism and live normal lives. The prognosis for well-managed hyperthyroidism is excellent for the majority of cats.

Talk to a vet any time you notice changes in your cat’s behavior or physical health. Cats with hyperthyroidism often have subtle symptoms in the early stages of the disease that can be easily overlooked. Clinical signs of hyperthyroidism are similar to other medical conditions and endocrine disorders that require treatment by your vet. Diagnosing hyperthyroidism involves diagnostic tests to rule out other conditions. Be patient and work with your vet towards a definitive diagnosis so the right treatment can be given. If you’re worried your cat may have hyperthyroidism or another hormonal disorder, you can talk to a vet for advice in an online virtual care appointment through Vetster.

How do I know if my cat has hyperthyroidism?

Clinical signs of an overactive thyroid gland in cats include weight loss, increased appetite, high energy levels, and changes to the skin and coat. Cats with hyperthyroidism may also become irritable or restless, or may need to urinate frequently. Symptoms can be subtle in the beginning stages of the condition.

How long does a cat with hyperthyroidism live?

Cats with well-managed hyperthyroidism can live a normal lifespan. However, if hyperthyroidism is left untreated, the condition can become deadly and lead to organ and heart failure.

What happens if hyperthyroidism in cats is left untreated?

Without treatment, cats with hyperthyroidism experience a continued increase in metabolism, causing weight loss and stress on the heart. They also typically eat increasingly larger amounts of food and frequently vomit or have diarrhea, often missing the litter box. Untreated hyperthyroidism is eventually fatal, but most cats experience severe weight loss and deteriorating quality of life before it reaches that point.