Hyperthyroidism in cats is primarily caused by an overproduction of thyroid hormones (T3 and T4) due to enlargement of the thyroid glands in the neck. In most cases, this enlargement is due to a benign (non-cancerous) tumor called an adenoma or hyperplasia, which causes the glands to produce excess thyroid hormone uncontrollably
. The exact cause of this thyroid gland enlargement is not fully understood, but several factors have been suggested:
- Age: It is most common in middle-aged and older cats, typically over 10 years old
- Environmental factors: Exposure to flame-retardant chemicals (PBDEs) found in some furniture and carpeting, as well as organic pollutants, may contribute to the risk
- Diet: Some reports have linked hyperthyroidism to certain fish-flavored canned foods and high dietary iodine levels
- Indoor lifestyle: Cats that live predominantly indoors may have a higher risk
Rarely (less than 1-2% of cases), hyperthyroidism can be caused by malignant (cancerous) tumors of the thyroid gland
. In summary, hyperthyroidism in cats is mainly caused by benign thyroid gland tumors leading to excessive thyroid hormone production, with age, environmental exposures, and diet as possible contributing factors. The underlying cause of the gland enlargement remains unknown in most cases
