A "hyperthyroid cat" is a cat that has a medical condition called hyperthyroidism. This means that the cat's thyroid gland produces too much thyroid hormone, which can cause various symptoms and health problems. Full definition
For example, in the case of hyperthyroid cats with high blood pressure, weight loss (in spite of a voracious appetite) and hyperactivity may be the major clinical signs. (icatcare.org)
Broome MR, Peterson ME: Use of L - thyroxine supplementation after radioiodine therapy helps blunt the worsening of azotemia in hyperthyroid cats with pre-existing kidney disease. (animalendocrine.com)
The long - term prognosis for hyperthyroid cats treated with radioiodine is excellent. (animalendocrine.com)