Cats with hyperthyroidism have a thyroid gland that is producing excessive amounts of thyroid hormones. An overactive thyroid causes a dramatic increase in the body’s metabolic rate, leading to weight loss among other symptoms.
Hyperthyroidism, or ‘overactive thyroid’, 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:
As a result, an excess of thyroid hormones affects the function of virtually every organ system.
The reasons for the change in the thyroid gland are not fully known.
In 98% of cases, the enlargement of the lobe(s) is benign and non-cancerous. In these cases, diagnosis and treatment are both straightforward and successful. In the remaining 2% of cases, the enlargement is due to a malignant cancerous growth of the thyroid gland.
Whatever the cause of the enlargement, the result is the same – more thyroid hormones are released.
