e sse nt i al pets
T hat Crazy THYROID!
There are a lot of diseases that dogs and cats have in common with people. Diabetes, allergies, inflammatory bowel disease, and obesity, to name a few. Both species also can have thyroid gland problems. The interesting thing is dogs and cats are at different ends of the thyroid disease spectrum—cats only develop an overactive thyroid gland and dogs almost exclusively develop an underactive thyroid gland. People can have either, but not both. The thyroid gland is found in the neck. Dogs and cats have a lobe on either side of the trachea, but it can’t be felt unless it’s enlarged. Thyroid hormone (the gland that produces T4, which is converted into the active hormone T3) regulates the metabolic rate of every cell in the body. If there is more T4, the cells work faster. Less T4, and the cells slow down. Hyperthyroidism is just that—the cells are hyper and working overtime. The metabolic rate speeds up, leading to increased energy output. The affected cat is burning more calories all the time, even when sleeping, so it’s very hungry, losing weight, and shedding 38 | m a d i s o n e s s e n t i a l s
more. Overactive cells in the intestines can cause vomiting or diarrhea. Hyper cells in the heart lead to a faster heart rate and thicker heart muscles, which can eventually cause heart failure. Hyperthyroidism is the most common hormonal disease in cats and is caused by a small tumor in the thyroid gland. It’s most commonly seen in cats over 13 years of age. There isn’t an exact cause for the disease found, but it’s probably due to multiple factors. Excess iodine in the diet may play a role in development of hyperthyroidism. Iodine levels in cat foods vary widely, sometimes up to 10 times the daily recommended level. Cats who eat mostly a cannedfood diet, particularly with fish flavors or from pop-top cans, have three and a half times the risk of developing the disease over cats eating just dry food. Fire retardant chemicals (PBDEs) and persistent organic pollutants (PFAS) are found in higher levels in hyperthyroid cats. Genetics may also play a part, as some purebred cats, such as Siamese and Persian breeds, have a decreased risk of developing hyperthyroidism.
by Lori Scarlett, DVM I recently had a cat patient come in because she was losing weight and vomiting more. The owner said she was ravenously hungry, but just kept getting thinner. I looked back in the cat’s record and saw that she had been diagnosed with hyperthyroidism six months previously and started on daily medication, but the owner had only gotten a month’s worth of tablets and never followed up. When asked, the owner said she didn’t realize it was a lifelong disease. Treatment consists of either twicedaily medication, feeding a special prescription diet exclusively, or radioactive iodine treatment. Most people choose to medicate their cat daily. Methimazole blocks the production of T4, which decreases the amount in the body, slowing down the metabolism. It works well and doesn’t have too many side effects, but periodic blood work is needed to make sure the dose is correct and the cat isn’t becoming hypothyroid. The prescription diet Hill’s Y/D is formulated to be very low in iodine, containing just enough so that the cat
