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. (chai-online.org)
The condition is marked by enlarged thyroid glands and an excess of thyroxine thyroid hormone. (vetdepot.com)
(Source)(Source) Individuals with enlarged thyroid glands were found to have low levels of selenium (Source) and may be a factor for thyroid cancer risk. (groundedorganic.com)