Texas Veterinary Medical Journal, 1985. 47: p.19-25.
Hyperthyroidism (thyrotoxicosis) is a multisystemic disorder resulting from excessive circulating concentrations of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Feline hyperthyroidism occurs in middle- to old-aged cats; there is no breed or sex predilection. Functional thyroid adenoma (adenomatous hyperplasia) involving one or both thyroid lobes is the most common cause of feline hyperthyroidism. Thyroid carcinoma, the primary cause of canine hyperthyroidism, rarely causes hyperthyroidism in the cat. Although first described only six years ago, hyperthyroidism has become a common and extremely important disorder of the cat