Hyperthyroidism in the cat: ten cases

In ten neutered crossbred cats 10 to 14 years old and of both sexes, hyperthyroidism was evidenced by hyperactivity, weight loss despite increased appetite, frequent defecation with bulky stools, thirst, polyuria, moderately elevated temperature, increased heart rate and size, sometimes with murmurs and arrhythmias, and palpable enlargement of one or both thyroid lobes. The diagnosis of hyperthyroidism was confirmed on the basis of high serum concentrations of thyroxine (T4) and triiodothyronine (T3). In seven cats (6 treated by total thyroidectomy, 1 studied at necropsy), both thyroid lobes were variably enlarged, mottled, cystic, or nodular; in three cats, only one lobe required removal. Adenomatous goiter was diagnosed microscopically in all. In two, there also were foci of adenocarcinoma and in two others, foci suggestive of adenocarcinoma. Three of the nine cats having surgery were treated preoperatively to stabilize cardiac function. Most cats recovered from surgery rapidly and without complications but although every effort was made to spare at least one parathyroid gland in cats having bilateral thyroidectomies, two cats had transient signs of hypoparathyroidism, requiring careful monitoring of serum electrolytes and treatment with calcium and vitamin D2. All having bilateral thyroidectomies were subsequently maintained on treatment with l-thyroxine or, in one case, liothyronine (triiodothyronine).