Hyperthyroidism

Have you noticed your older cat suddenly acting a bit more spry and energetic, eating more, yet losing weight? Well this presentation is not too uncommon, and high on the list of possibilities is an endocrine disorder known as hyperthyroidism. Whereas the most common thyroid disorder in a dog is hypothyroidism, or a low functioning thyroid, in the cat it is a high functioning thyroid. And, what is so unique to this feline problem is that the underlying problem is that of a benign, functional, thyroid adenoma, meaning the over-grown, overactive thyroid tissue is not a malignant problem, and the remaining gland itself remains totally normal.

The typical affected cat is usually on the older side-often over ten years of age, in fact one of my first cases in practice was a 17 year old cat! These cats are usually a little over-active, are eating well, but are thin, may have dry coats, faster than normal heart rates, and often have what we call palpable thyroid glands in the neck. Laboratory work will often reveal elevated liver enzymes, and increased thyroid hormone levels. There are a few thyroid tests that are typically run, the t3, t4, and the free t4 by equilibrium dialysis. Most senior feline blood panels include all three of these, but the one that many of us find the most specific is the free t4 by equilibrium dialysis, since it seems to be the most specific, and less affected by other aspects of the cat's physical state. Since other "old cat" diseases can have similar presentations, the blood test is so important to make an accurate diagnosis. Also, since this condition does seem to affect older cats, a complete senior physical including x-rays and an ECG should be a part of the minimum data base, both for diagnosis and to assess pre-treatment overall health.

If the blood tests seem to support the diagnosis of hyperthyroidism and everything else checks out, the next step is to consider a thyroid scan to confirm the diagnosis. This scan may not always be necessary, but is recommended, especially if the option of radiation treatment will be chosen.

There are a few treatment options available, though one, radiation, seems to be the favorite of most. This is the method used to treat people with the same condition, and what is so nice about it is that it is fairly non-invasive, destroys only that portion of the gland that is abnormal, and, because the normal tissue remains untouched and functional, post treatment thyroid supplements are rarely needed. The downside is the fact that the treatment is a little on the costly side (though very worth it! ), and that these cats often need to stay at the radiation facility for a few days during and after the treatment. The next method, surgical removal of the affected gland or glands, is still an option. Since the advent of the radiation treatment, surgery isn't performed nearly as often. For one thing, in the case of bilateral disease, these cats will need a thyroid supplement for the rest of their lives. Also, it is often difficult to preserve the tiny parathyroid glands which lie within the thyroid capsule, so if these are destroyed or removed, the cat will also need a supplement to help regulate calcium and phosphorous balance as well. And, of course, surgery requires anesthesia, often on a compromised cat, so one needs to consider those risks as well. Lastly, for extremely old or infirm cats, or if the other options are not affordable, an oral medication called methimazole can be used to help combat the effects of the increased thyroid hormone on the body. This treatment doesn't get to the root of the problem, but it can help with the symptoms.

Even with successful treatment, these cats need to be monitored closely. With the return to a euthyroid, or normal thyroid status, other conditions such as weakened kidneys, which may have been masked by the increased blood flow during the hyperthyroid state, may now begin to elicit symptoms of disease. Should you have any questions or concerns, make sure to see your veterinarian.