what is hyperthyroidism called
What is hyperthyroidism? Hyperthyroidism is a very common disease afflicting primarily middle-aged and older cats. Also called thyrotoxicosis, hyperthyroidism is caused by an increase in production of thyroid hormones (known as T3 and T4) from enlarged thyroid glands in the cat's neck. In most cases, enlargement of thyroid glands is caused by a tumor called an adenoma, which is non-cancerous.