Labuc R.H. and Jones B.R.
Feline hyperthyroidism is the name given to the multisystemic manifestation of excessive concentrations of circulating thyroid hormones, thyroxine (T4) and tri-iodothyronine (T3). The most common cause is a functional thyroid adenoma involving one or both thyroid lobes. Both multinodular adenomatous hyperplasia and multinodular adenomatous goitre are acceptable descriptions for the histopathological findings. Thyroid adenocarcinoma rarely causes hyperthyroidism in the cat, and when present, seldom metastasizes.