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The Bad Weight Loss Program: Thyroid Disease in Cats


The thyroid gland, located on the underside of the neck in animals, can be a source of problems for pet owners. Cats and dogs each tend towards opposite end of the spectrum with thyroid disease. Cats tend to get thyroid tumors, which produce too much thyroid hormone, leading to significant weight loss. Dogs tend to have under-active thyroids, causing weight gain. Either problem can have significant health effects for pets.


Our feline companions commonly grow benign thyroid tumors, which produce excessive thyroid hormone, causing a cat’s metabolism to go into overdrive. These cats typically become voraciously hungry, and can eat almost constantly and still lose weight. Affected cats may also drink excessive water, vomit, have diarrhea, and become more vocal at night, waking up their owners with yowling. Left untreated, a persistently high thyroid level can cause heart damage, kidney damage, weakness and lethargy and severe high blood pressure, which can lead to blindness and further organ damage.


Detecting a high level of thyroid hormone, often called T4, is done through a simple blood test. May veterinarians now recommend screening older cats yearly for this disease, since the symptoms can be subtle in the early stages. On physical exam a veterinarian may notice an elevated heart rate, high blood pressure, a heart arrhythmia or feel a thyroid nodule, which will increase the level of suspicion.


One reason thyroid tumors are becoming much more common in cats is because of the proliferation of flame retardants. Chemicals, called PBDE’s, applied to upholstery and carpets may be linked to increasing the risk of thyroid tumors in cats. Luckily, the cancerous form of these tumors is uncommon.


Excessive amounts of the T4 hormone, in cats can be managed in several ways. Medication (methimazole) can bring the thyroid level down, though it then must be given for the rest of the cat’s life. Regular monitoring should be done to insure that the kitty is receiving the proper dose of medication. Surgery offers a more permanent solution. Since the thyroid gland is divided into two distinct halves, the side containing the tumor can be removed..  Another option is to destroy the tumor by injecting the cat with radioactive iodine at a specialty hospital. While both of these remedies are permanent, new tumors can appear later. More recently, Hill’s Science Diet released a prescription food that helps to regulate thyroid disease as well. The severely iodine restricted food works well, but should be the only thing a cat eats.


Thyroid disease is unfortunately very common in today’s pet cats. Luckily, when caught early, the disease is very manageable. If your cat is losing weight while eating normally, make plans to give your kitty a check up with your local veterinarian right away!


Michael J. Rumore, D.V.M.