Feline Hyperthyroidism
The thyroid is a gland that consists of two connected lobes and is situated in the neck area of cats (and dogs and humans!). The thyroid gland plays a very important role in regulating the body's rate of metabolism. Many organs are affected by the hormones released from the thyroid, including: the heart and kidneys. Hyperthyroidism is a disorder characterized by an overproduction of thyroid hormone. This is a fairly common disorder in middle aged to older cats.
The most common symptom of hyperthyroidism is weight loss despite a normal or increase in appetite. Some cats, exhibit such a profound increase in appetite that they seem overly restless or over-active. Despite the increase in food intake, these kitties just can't seem to maintain their body weight because of the excess thyroid hormone driving their metabolism. Affected cats often drink a lot of water and urinate more as well. There may also be periodic vomiting or diarrhea and a poor quality haircoat. In some cats, their appetite decreases as the disease progresses.
There are two main complications of hyperthyroidism: Hypertension (increased blood pressure) and Heart Disease. In some cats, their blood pressure becomes so high that it damages the retina of the eye causing blindness. The heart will often become enlarged and thickened, making heart murmurs, heart failure, and blood clots develop.
The most common symptom of hyperthyroidism is weight loss despite a normal or increase in appetite. Some cats, exhibit such a profound increase in appetite that they seem overly restless or over-active. Despite the increase in food intake, these kitties just can't seem to maintain their body weight because of the excess thyroid hormone driving their metabolism. Affected cats often drink a lot of water and urinate more as well. There may also be periodic vomiting or diarrhea and a poor quality haircoat. In some cats, their appetite decreases as the disease progresses.
There are two main complications of hyperthyroidism: Hypertension (increased blood pressure) and Heart Disease. In some cats, their blood pressure becomes so high that it damages the retina of the eye causing blindness. The heart will often become enlarged and thickened, making heart murmurs, heart failure, and blood clots develop.
Hyperthyroidism is diagnosed by checking on the total amount of thyroid hormone (T4) in the blood. Usually, the T4 level is so high that the diagnosis is straightforward. Occasionally, a cat suspected of having hyperthyroidism will have normal or only slightly elevated T4 levels and an additional test is needed to assess a different version of the thyroid hormone.
Blood should also be used to evaluate the cats liver and kidney function as these organs are often damaged secondary to excess thyroid hormone.
Blood should also be used to evaluate the cats liver and kidney function as these organs are often damaged secondary to excess thyroid hormone.
Management of hyperthyroidism is generally very successful. Complications of treatment can occur if there is underlying kidney disease and a small percentage (less than 2%) of cats will have a cancerous growth of the thyroid gland. Kidney disease is another common occurrence in senior cats and the beginning stages of kidney disease can be masked by hyperthyroidism. Once the thyroid level is brought under control, the cat's kidney bloodwork values should be closely monitored for increases that would require additional therapies. There are several treatment options and your veterinarian will discuss the pros and cons of each as they relate to your individual pet.
Treatment options may include:
1) Methimazole administration- this is one of the most common therapies used to treat hyperthyroidism. This is a medication that can be formulated as an oral tablet, oral liquid, or transdermal gel. Methimazole decreases the amount of thyroid hormone produced, but it is a long term medication - if discontinued, the thyroid hormone level will rise again. Generally well tolerated by most patients, bloodwork is necessary to determine the proper dose and monitor for side effects. For cat owners that wish to pursue more "permanent" therapy for hyperthyroidism such as radioactive iodine or surgical intervention, methimazole is still recommended for initial thyroid stabilization.
2) Y/d dietary therapy- this is a newer option to treat hyperthyroidism using an ultra low iodine diet. The body uses iodine in the production of thyroid hormone, so low iodine levels in the diet leads to lower thyroid hormone production. In order for this method to work, it is absolutely vital that the cat receives NO OTHER FOOD other than Y/d (which comes in dry kibble and canned). Iodine is not regulated in ANY other food / treat, so any nibble of any other source of food (pet or human) will invalidate this therapy. It is so important to avoid even residues of other diets that new food bowls are needed.
3) Radioactive iodine treatment- radioactive iodine is given by injection and it destroys all abnormal thyroid tissue without endangering other organs. Treatment requires 5 to 7 days of hospitalization at a specialty referral center such as the University of Illinois in Champaign.
4) Surgical removal of the thyroid- surgical removal of the thyroid gland is also an option, although this is the most invasive method.
Treatment options may include:
1) Methimazole administration- this is one of the most common therapies used to treat hyperthyroidism. This is a medication that can be formulated as an oral tablet, oral liquid, or transdermal gel. Methimazole decreases the amount of thyroid hormone produced, but it is a long term medication - if discontinued, the thyroid hormone level will rise again. Generally well tolerated by most patients, bloodwork is necessary to determine the proper dose and monitor for side effects. For cat owners that wish to pursue more "permanent" therapy for hyperthyroidism such as radioactive iodine or surgical intervention, methimazole is still recommended for initial thyroid stabilization.
2) Y/d dietary therapy- this is a newer option to treat hyperthyroidism using an ultra low iodine diet. The body uses iodine in the production of thyroid hormone, so low iodine levels in the diet leads to lower thyroid hormone production. In order for this method to work, it is absolutely vital that the cat receives NO OTHER FOOD other than Y/d (which comes in dry kibble and canned). Iodine is not regulated in ANY other food / treat, so any nibble of any other source of food (pet or human) will invalidate this therapy. It is so important to avoid even residues of other diets that new food bowls are needed.
3) Radioactive iodine treatment- radioactive iodine is given by injection and it destroys all abnormal thyroid tissue without endangering other organs. Treatment requires 5 to 7 days of hospitalization at a specialty referral center such as the University of Illinois in Champaign.
4) Surgical removal of the thyroid- surgical removal of the thyroid gland is also an option, although this is the most invasive method.
This cat is receiving methimazole as a transdermal gel- a low stress method to provide medication. Transdermal gels have a lotion-like consistency and when applied to the inner ear flap allows the drug to be absorbed through the skin.
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Click on the image to watch an informational video on Hill's Prescription Diet Y/d
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