| 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. |