As your cat ages, a variety of common health problems can begin to manifest. One such issue is Feline Hyperthyroidism, a serious and prevalent condition. Thankfully, with proper diagnosis and treatment, cats affected by hyperthyroidism can live normal, healthy lives.
The thyroid is a small gland found in most mammals, including cats. It is located at the base of the neck and produces the thyroid hormone thyroxine, which regulates the body’s metabolism. In dogs and humans, hypothyroidism (underproduction of thyroid hormone) is more common, leading to a slow metabolism. While cats can occasionally develop hypothyroidism, they are far more likely to develop hyperthyroidism, where the thyroid becomes overactive and produces too much hormone. This results in an accelerated metabolism. Although hyperthyroidism is typically a benign condition (not usually associated with cancer), it is serious and can lead to severe health problems or even death if left untreated.
Because the thyroid affects nearly every organ and cell in the body, hyperthyroidism can cause a wide range of symptoms and warning signs. Generally, this condition occurs in middle-aged to older cats, with no significant sex or breed predisposition.
Some of the main symptoms of hyperthyroidism include:
- Weight loss despite a ravenous appetite: As the thyroid increases the body’s metabolism, the cat may become insatiably hungry, yet may still lose weight rapidly.
- Increased thirst and urination: This can include inappropriate urination (e.g., outside of the litter box) and even blood in the urine. Excessive water intake can also put additional strain on the kidneys, potentially leading to kidney damage.
- Behavioral changes: Hyperactivity, nervousness, and irritability may occur due to the increased metabolism. However, some cats may show the opposite symptoms, becoming weak, lethargic, or experiencing “manic” periods of extreme activity followed by long stretches of lethargy.
- General appearance: Cats with hyperthyroidism may have a rough, unhealthy coat that sheds more than usual. Their nails may also become thick and brittle.
- Gastrointestinal upset: Vomiting and diarrhea are also possible symptoms of hyperthyroidism.
- Cardiovascular changes: Untreated hyperthyroidism puts significant strain on the heart and respiratory system. Many cats experience rapid breathing and a fast, strong heartbeat that can be easily felt by placing your hand on the cat’s chest. This condition, known as myocardial hypertrophy, can cause irreversible cardiac damage.
Hyperthyroidism affects many vital organs and physiological functions. If left untreated, it can lead to dangerous and even fatal consequences. In addition to routine yearly physical exams by your veterinarian, any cat showing symptoms of hyperthyroidism should be examined immediately. Your vet will review your cat’s medical history and ask for details about any changes in activity levels, behavior, or other warning signs. A physical exam may reveal signs such as an enlarged thyroid gland (a common symptom), and your veterinarian may check for heart dysfunction and measure blood pressure.
If hyperthyroidism is suspected, blood tests are one of the most effective ways to diagnose it. A Complete Blood Count (CBC) and Blood Chemistries will assess your cat’s overall health and examine organ function, such as the kidneys and liver. The CBC evaluates red blood cells, white blood cells, and platelets, helping to diagnose conditions like infections and anemia.
To specifically diagnose hyperthyroidism, a thyroxine (T4) test is performed. Elevated T4 levels strongly indicate hyperthyroidism, but false negatives can occur. To confirm the diagnosis, your vet may also perform a Free T4 (FT4) test, which is more sensitive and provides a definitive result.
If your cat is diagnosed with hyperthyroidism, your veterinarian may recommend additional diagnostic imaging (e.g., radiographs and ultrasound) to ensure there are no underlying causes, such as tumors or other forms of cancer.
The exact cause of hyperthyroidism in cats is often unknown, but treatment is typically straightforward and very successful. There are two main options: medication or radiation therapy.
The appropriate treatment depends on your cat’s individual health and condition. Several tests may be conducted before deciding on the best course of action. Once the tests are completed, a personalized treatment plan can be created for your cat.
Medication is the most common and generally the least expensive treatment. This involves giving your cat medication twice daily for life, which can be in the form of pills, liquid medication, or transdermal gels. However, treatment depends on the owner’s ability to ensure the cat takes the medication consistently, and the cat’s willingness to ingest it.
A newer treatment option is radioiodine therapy, a one-time radiation treatment. This involves injecting radioactive iodine directly into the thyroid gland, which destroys only the abnormal cells responsible for overproducing thyroxine. Often, one treatment is enough to “cure” the cat, eliminating the need for daily medication. However, this is a more invasive treatment that requires a multi-day hospital stay and a larger financial investment.
Regardless of the treatment method chosen, follow-up bloodwork is a key part of successfully managing hyperthyroidism. After starting medication or undergoing iodine therapy, your veterinarian will likely recommend several rounds of follow-up tests to adjust medication doses and confirm the success of the radiation treatment. Over time, as your cat stabilizes, blood tests may become less frequent, but all cats being treated for hyperthyroidism should have their T4 levels checked at least twice a year to ensure their treatment is still effective.
While hyperthyroidism in cats can be dangerous and potentially fatal, it is highly treatable. Cats who receive proper treatment for hyperthyroidism often develop no secondary illnesses and go on to live long, healthy lives.
