Forty years ago, this disease was unknown in cats but over time, it has become the most common endocrine disease affecting our feline friends. Hyperthyroidism is a disease that affects the production of thyroid hormones known as T3 and T4. They circulate around the blood stream and affect every organ in the body controlling their metabolism (that is how fast the body uses energy). The heart is especially affected by these hormones. An increase in these T3 and 4 hormones increases the heart rate, causes irregular heart-beats and possibly heart failure. Kidney disease is often seen in conjunction with hyperthyroidism, but it is not directly caused by an overactive thyroid gland. Rather, treatment of hyperthyroidism reveals other diseases that had previously been masked by the excessive hormones.
So, what are the signs of a cat suffering from hyperthyroidism? Think of a cat that is “hyper”, so it becomes skinny losing a lot of body muscle; it is vocal and more active or restless than normal; your cat also has increased hunger and thirst. Usually, your cat is over seven years of age as this is not a disease of younger cats. Although the clinical signs suggest hyperthyroidism, it does need to be diagnosed by blood testing.
The disease first appeared in the 80’s and 90’s and quickly spread around the globe. Because of its recent appearance, it is assumed that hyperthyroidism must be man-made, either due to diet or environment but, as yet, no definitive cause has been established.
There are four methods of treating the disease, each with a variable success rate. As the thyroid relies on the uptake of iodine to function, eliminating iodine from the diet can reduce the output by the thyroid gland. There are prescription diets that do this but are only successful in single cat households, where your pet does not go outside. In areas close to the sea, there is too much natural iodine around for this method work.
Daily medication with drugs to reduce the thyroid gland output work well. Tablets or liquids are given once or twice a day and are effective, but regular blood tests are required to monitor the treatment and ensure other diseases are not present.
Surgery to remove the overactive gland is highly effective but does carry risks especially of damaging the tiny parathyroid glands next to it.
The most recent development in treatment therapy is radioactive iodine. This has shown to be highly effective, safe and only one dose is needed to permanently treat the disease. The radioactive iodine targets and kills the abnormal cells. However, it is expensive and needs hospitalisation for several days. As more specialist referral services offer this procedure, the costs have reduced, and a one-off treatment is comparable in price to lifelong daily medication.
Future research may reveal the cause of this disease, but in the mean- time there are effective treatments available so if your cat is losing weight, please get it checked.