What is Hyperthyroidism?
A brief description
Cats with hyperthyroidism have a thyroid gland that is producing excessive amounts of thyroid hormones. This causes a dramatic increase in the body's metabolic rate.
Hyperthyroidism occurs when the thyroid gland over–produces thyroid hormones. Your cat's thyroid gland is located in its neck. It is divided into two parts called lobes which lie on either side of the windpipe (trachea).
When a cat has hyperthyroidism either one or both of the thyroid lobes become enlarged (both lobes are affected in 70% of cases). This leads to excessive production of the thyroid hormones T4 (also known as thyroxine) and T3 (also known as triiodothyronine).
These hormones:
- Are essential to proper growth of body cells and the development of these cells for specific roles in the body.
- Help regulate the metabolism of protein, fat and carbohydrate by cells.
- Are involved in the regulation of heat production and oxygen consumption and therefore a wide–range of metabolic processes.
As a result, an excess of thyroid hormones affects the function of virtually every organ system.
Excess thyroid hormones
In cats with hyperthyroidism the excess of T4 and T3 in the blood causes a large increase in the metabolic rate. As the metabolism of each cell increases they require more energy to function. This means that a cat with hyperthyroidism has to eat a lot of food to provide this energy.
As the condition progresses it becomes increasingly difficult for a cat to eat enough to provide the huge amount of energy required so they start to lose weight. This is why the most common clinical sign in cats with hyperthyroidism is weight loss despite a ravenous appetite.
The increased metabolic rate also causes other signs including restlessness and a rapid heart rate.
