Thyroid carcinoma causing hyperthyroidism in cats: 14 cases (1981-1986)

The medical records of 14 hyperthyroid cats with thyroid carcinoma were analyzed retrospectively regarding historical, physical, laboratory, and thyroid scintiscan findings, treatment, and treatment outcome. Breed predilection was not detected, and older castrated male cats were most commonly affected. The most common clinical signs detected by owners were weight loss, polydipsia, polyuria, polyphagia, hyperactivity, and anorexia. Physical examination findings included tachycardia, palpable cervical mass, hyperactivity, cardiac murmur, and abnormal coat. Common abnormal laboratory findings were high serum thyroxine and triiodo-thyronine concentrations and high serum alanine transaminase, alkaline phosphatase, and aspartate transaminase activities. Azotemia, hyperphosphatemia, and hyperglycemia were noticed less frequently. The most common thyroid scintiscan findings were multiple nodular areas of high radionuclide uptake in the cervical region, thoracic inlet, and cranial mediastinum. The most common morphologic diagnosis was mixed compact and follicular carcinoma, with follicular and papillary carcinomas being less common. Most cats responded well to treatment of the thyroid tumor, with rapid resolution of the historical and physical examination findings. The most common necropsy findings were local tumor invasion, regional lymph node metastases, cardiomyopathy, and interstitial nephritis.