Hyperthyroidism is a very common disease of the middle aged to older cat. A tumor (which is almost always non-cancerous) on the thyroid gland starts producing too much thyroid hormone. Symptoms are usually weight loss in spite of a great appetite, and vomiting. Other signs you might see are diarrhea, a dull and flaky hair coat, and personality changes. Hyperthyroidism often can cause heart disease and high blood pressure. This disease usually can be easily diagnosed with a blood test.
There are three basic methods of treatment: An oral medication called methimazole (Tapazole); radioactive iodine treatment; or surgery. For most cats the oral medication works well.
There is also a new pet food out on the market from Science Diet that controls your pet’s thyroid level by diet alone. This food is the only food that your pet can eat however, so in some households it may not work well, but it is a great alternative for treating a pet that doesn’t like oral medication. Your veterinarian will need to check blood work after starting the diet to be sure it is working.
The disease of hyperthyroidism can actually help the kidneys, and can sometimes mask underlying kidney disease. If the cat has both kidney disease and hyperthyroidism, it is not a candidate for radioactive iodine and the dose of Tapazole may need to be adjusted. Kidney function must be monitored when a cat is being treated for hyperthyroidism.