Hyperthyroidism is a relatively common hormone disorder in older cats. It is extremely uncommon in dogs. Hyperthyroidism is caused by a tumour of the thyroid gland which creates excessive levels of thyroid hormone. Since thyroid hormone is the master control hormone for body metabolism, this causes the metabolism of these cats to be very high. One of the most significant effects of this disease in cats is the effect that hyperthyroidism has on blood pressure. Hypertension (high blood pressure) is a direct symptom of this disease which results in significant damage to the kidneys and the heart over time. These cats will classically present with a significant recent weight loss, a ravenous appetite, an abnormal coat, and signs of kidney failure (drinking excessively and urinating often).
If we have the opportunity to diagnose this condition early it is quite easily managed and our patients will do well for many years. However if the cat has been suffering with the condition for a long time they will often have kidney failure and heart problems that are very challenging to manage. Hyperthyroidism can be easily detected using a simple blood test. Cats that are diagnosed as being hyperthyroid are put on a drug called methimazole (Tapazole is the trade name) that interferes with the manufacture of the active form of thyroid hormone. This drug is even available in a “transcutaneous” form and is given to the cat by rubbing it on the inside of their ear! This rapidly restores the “normal” level of thyroid hormone to their system by reducing the level of active hormone produced by the tumour tissue. Once on their treatment these cats very quickly become more normal, both physically and mentally. They put weight back on, their blood pressure drops dramatically, their heart rates slow and their appetite decreases to normal levels. There are other methods of treating this disease as well. These include radioactive iodine therapy to actually kill the cancer as well as a new food available from Hill’s called Y/D that may be useful in controlling some cats.
It is quite common to include the blood test for hyperthyroidism in routine blood screening panels for older cats. Your veterinarian will often bring this up if they feel that your older cat has been losing weight a bit too rapidly. This is one of those diseases which requires a history of regular visits to the veterinarian to spot the weight loss as these cats age. It is also one of the diseases that older cats develop that respond extremely well to management.
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