Hyperthyroid disease increases the metabolic rate and the blood pressure. Both of these processes are damaging to the kidneys and heart.
Hyperthyroidism will increase the blood pressure and force the kidneys to work harder, making the kidneys appear as though they are doing a better job clearing toxins than they are capable of doing when the blood pressure is normal. This means that after your cat is treated for hyperthyroidism, his recheck blood work may demonstrate elevated kidney values.Yet even though the kidneys may appear "worse" after treatment for hyperthyroidism, as long as your cat has reasonable function remaining, your cat's kidney function will last longer as the damaging effects of hyperthyroidism have been removed.
Hyperthyroidism tends to increase the metabolic rate, and frequently causes the heart to beat harder and faster than normal, leading to hypertrophic cardiomyopathy, were the walls of the heart become thickened, resulting in decreased efficiency of the pumping of the heart. If the condition is severe, stress or sudden exertion can cause animals to suddenly decompensate and develop life threatening abnormal heart contractions and rhythm.
There are multiple ways to treat hyperthyroidism. On initial diagnosis we will start your cat on an oral medication or diet that will help to lower the T4 level in your cat. This allows us to check for any underlying kidney disease. If severe kidney disease is uncovered we may want to try to preserve a mild state of hyper thyroidism to continue to maintain a degree of kidney function.
Methimazole is a drug which eats away thyroid tissue, decreasing the levels of the thyroid hormone responsible for the increased metabolism. Methimazole is usually a life-long medication that requires daily administration. The most common side effect is vomiting. While on Methimazoel we recommend monitoring of blood levels of thyroid and kidney values every 6-12 months.
Another method is a relatively new diet manufactured by Hill's called y/d. It is greatly reduced in iodine, which is necessary for the body to form thyroid hormone. Because most other diets and treats contain iodine, it must be fed to the cat as a sole diet and no other food or treats. It is also a life-long treatment and will require monitoring thyroid and kidney numbers similar to the monitoring required for Methimazole.
If after achieving an appropriate dose of the medication called Methimazole and determining the underlying kidney health of your cat we can either maintain your cat on the oral medication or discuss more permanent forms of therapy that do not require daily medicating. Methimazole does not control the physiologic symptoms of hyperthyroidism as well as the radio-iodine treatment, but it is certainly preferable to no treatment.
The most preferable method is with an injection of radiolabeled iodine. This is usually a one-time treatment and it usually controls the physiologic problems, especially cardiac problems, very well. If this is not an option then the oral medications must be given for the rest of the cat's life.