This is the scan of a normal cat. Both lobes of the thyroid gland are visible.
Hyperthyroidism is a disease of older cats that we have diagnosed with increased frequency in recent years. It is almost always caused by a benign tumor of the thyroid gland that increases the amount of thyroxine (the hormone secreted by the thyroid gland) in the bloodstream. This increase in thyroxine causes an increase in the overall metabolism of the body, leading to problems for several internal organs. Even though this disease can be diagnosed in young cats, most cats that get this problem are older. Cats 8 years of age or older should be screened for this problem when routine blood panels are run.
Cats that have Feline Hyperthyroidism commonly have other problems that need careful attention if the thyroid problem is to be treated successfully. The excess thyroxine can cause these other problems, or make them worse if they already exist. Some of these other common problems are kidney disease, heart disease, dental disease, sugar diabetes (diabetes mellitus) and high blood pressure (hypertension) leading to blindness.
The symptoms that occur depend on which internal system or systems are most influenced by the increase in thyroxine circulating throughout the bloodstream. The more common ones are:
During a physical exam some cats will appear thin and have racing heart rates and even heart murmurs (click here if you would like to hear what a murmur sounds like). In some cats we can feel an enlarged thyroid gland. You might notice our doctors palpating your cat's neck and throat during an exam to check for this enlargement. Some cats can have an enlarged thyroid gland that can not be palpated because it has slipped from its normal position at the throat and repositioned itself further down the chest.
An important tool in the diagnosis of Feline Hyperthyroidism is a blood panel. We can sometimes detect the effects of the excess thyroid hormone on the internal organs by running a routine blood panel. In addition to this blood panel we run a specific thyroid test which is frequently all we need to make the diagnosis. Since thyroxine levels fluctuate, we occasionally need more sophisticated tests to make an accurate diagnosis.
One of the most precise tests to diagnose hyperthyroidism is a scan of the thyroid gland. Not only is this test accurate in diagnosing the problem, it will let us know if some of the abnormal thyroid tissue has repositioned itself further down the chest. An additional benefit is its ability to detect a malignant cancer of the gland in the rare occasion that this occurs.
This is the scan of a normal cat. Both lobes of the thyroid gland are visible.
This cat has Feline Hyperthyroidism. It is the more common benign version, and is present in only one lobe of the gland.
There are three primary methods of treating this disease. Each has its advantages and disadvantages, and depends on your unique situation. One of our doctors will discuss all these options with you before instituting any treatment:
The treatment of choice involves the use of radioactive Iodine to selectively destroy only the part of the thyroid gland that has a problem. It has the advantage of a very high success rate and does not require anesthesia. It will also destroy the diseased thyroid tissue that has moved towards the chest. The disadvantage is the fact that your cat must be boarded at the treatment facility for up to 10 days after treatment to minimize radiation exposure to others. Approximate cost is $700. This treatment is done at a special center, and is available only on a referral by one of our doctors. The center that performs the scan to make the diagnosis is the same place that will institute this treatment.A relatively common treatment is the use of a drug called Tapazole. It is inexpensive and easy to give to most cats. Disadvantages are the fact that it never cures the problem, so a cat will need to be on it long term, and occasional cats get side effects to the drug. It is used in cats that have chronic renal failure, a common problem as cats age. In these cats the excess thyroxine circulating can actually be an advantage to the kidneys because it increases the blood flow to the kidneys. This makes them more efficient at removing waste products. If we completely destroy the excess thyroid tissue with radiation or surgery, a kidney problem that was under control can now become serious. In these situations we administer a dose of Tapazole that decreases the excess thyroxine enough to make your pet feel a little better, but not so much that it will exacerbate a kidney problem that is being masked. It is a compromise in therapy because it is an attempt to balance two problems that are occurring simultaneously.
Surgery is also used to treat this condition, and can be very effective. It has the advantage of a rapid and successful cure rate. Its disadvantages are the need for anesthesia and its inability to remove diseased thyroid tissue that is in the thorax. Some cats can also get a problem maintaining normal calcium levels after surgery.
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