Feline Hyperthyroidism is a disorder that occurs when the feline thyroid gland produces an excess of thyroid hormone. An excess of thyroid hormone affects all of the cat’s organ systems. Feline Hyperthyroidism can occur in cats as young as 2 years old, but it’s more common in senior cats. Both male and female and all breeds are equally at risk.
The thyroid gland is butterfly-shaped and is located in the neck region of the cat. Hyperthyroidism is caused by a tumor in this gland that produces excessive amounts of thyroid hormone. Ninety eight percent of these tumors are benign (adenoma) and two percent are cancerous (carcinoma).
Seventy percent of cats have both lobes of the thyroid gland affected. Symptoms of Feline Hyperthyroidism in cats may include: weight loss, changes in behavior, anxiety or nervousness, excessive appetite or decreased appetite, increased water drinking, hyperactivity or lethargy, excessive shedding, hair loss (alopecia), poor coat condition, diarrhea or vomiting, increased urination, cardiac symptoms, rapid heart rate or arrhythmia.
Your Veterinarian will make a diagnosis of hyperthyroidism when your cats level of thyroid hormone is higher then normal. Most hyperthyroid cats have very high levels of thyroid hormone. Thyroid hormone levels can vary over time so it may be necessary to check blood levels several times or perform a test called a T3 suppression test. Sometimes the thyroid gland can be so enlarged that is felt in the neck. If the thyroid levels are not too high and a diagnosis is not obvious by blood tests, a nuclear medicine scan of the thyroid glands can be performed at certain specialty veterinary practices.
The scan is performed by injecting your cat with a small dose of a radioactive Iodine. Thyroid glands are sponges for iodine, so the radioactive iodine (RAI) is quickly absorbed by the thyroid gland. You cat’s scan will take a picture of your cat and the size and shape of the thyroid gland will be easily seen. Hyperactive thyroid tissue will absorb more of the compound than a normal gland. If a tumor is present it will show up clearly in the nuclear scan. Because your cat will be radioactive for a few days, the cat must be hospitalized while it clears the RAI from its body.