Hyperthyroidism is the most common endocrine (hormone) disorder that affects cats. It creates a wide range of signs resulting from the overproduction of thyroid hormone made by the thyroid gland.
Causes of Hypothyroidism in Cats
If the thyroid gland produces excess amounts of the thyroid hormones, the condition called hyperthyroidism results. The most common cause is a benign (non-cancerous) increase in the number of cells in the thyroid gland. Groups of these abnormal cells form small nodules on the thyroid gland and are termed adenomas. Multiple adenomas may form in the same lobe, and in approximately 70% of the cases, both lobes are involved. Only 1-2% of hyperthyroid conditions in cats are caused by malignancy (cancer).
The incidence of hyperthyroidism in cats has increased remarkedly in the last 25 years. The reason for this is unknown, but probably due to multiple factors. The ingredients and types of foods fed, immunological factors, and environmental influences may be involved.
Which cats are Most Likely to become Hyperthyroid?
Hyperthyroidism occurs most commonly in middle to old-age cats with a reported range of onset between 4 and 22 years. The median age for acquiring the disorder is just under 13 years. Only 5% of hyperthyroid cats develop the disease before 8 years of age. There does not appear to be a breed or sex predilection.
Treatment for Hypothyroidism in Cats
Rapid heart rates are common in cats with hyperthyroidism, and heart murmurs and high blood pressure can also occur. Cats with hyperthyroidism that are not treated often develop a heart condition called hypertrophic cardiomyopathy, in which the muscle of the heart becomes excessively thick. This can lead to heart failure and death.
There are currently three ways to treat hyperthyroidism in cats:
1. Medical treatment with the anti-thyroid drug, methimazole
2. Surgical removal of the affected gland
3. Treatment with radioactive iodine
