Spontaneous Hyperthyroidism in the Cat: An Animal Model for Toxic Nodular Goiter

Peterson M.E. and Becker D.V.

Conference Proceedings, (1983). Proceedings of the 59th annual meeting of the american thyroid association: p.T-31


In 150 aged cats with spontaneous hyperthyroidism, the most frequent clinical signs included weight loss, polyphagia, irritability, tachycardia, polyuria, and diarrhea. Diagnosis of hyperthyroidism was based on elevated serum T4 (mean SEM = 14.7 ± 0.8 mg/dl; normal = 0.8 to 3.8 mg/dl) and T3 (mean = 296 ± 17 ng/dl; normal = 15 to 104 ng/dl). 131I thyroid uptake (RAIU) at 24 hours in 35 cats ranged from 19 to 58% (normal = 9.2±0.6%). Thyroid kinetic studies in 30 cats defined 2 groups: 13 with higher mean peak RAIU (56.8% vs 34.2%) than 17 cats with slower 131I turnover (mean = 14 vs 8.1 hours-1). Mean T4 and T3 levels in the rapid turnover group were significantly higher (P < 0.002) than the slower turnover group (T4 = 25.2 vs 10.5 mg/dl; T3 = 504 vs 220 ng/dl). Thyroid imaging showed enlargement and increased uptake in both lobes in 70% and in one lobe in 30%. Hemi- or total thyroidectomy was used as treatment in 85 cats. In 55, propylthiouracil (PTU) was given before surgery for 3 to 6 weeks to normalize serum T4 and T3. In the remaining 30 cats not treated with PTU, T4 and T3 decreased to normal within 48 hours of thyroidectomy. Histopathology revealed adenomatous hyperplasia of 1 or both thyroid lobes in all cats. In cats with 1 lobe involvement, repeat imaging after hemithyroidectomy showed return of normal function in the previously suppressed remaining lobe. In 15 cats treated with 131I (1 to 5 mCi), T4 and T3 normalized in 2 to 9 days (mean = 4.1); hypothyroidism developed in 2, while 2 relapsed necessitating retreatment. PTU was used as sole treatment in 20 cats. Serious drug reactions, including anemia, thrombocytpenia, and lupus-like reaction, occurred in 6 cats treated with PTU. In conclusion, feline hyperthyroidism is a common, easily diagnosed, and treatable disease. The frequency and analogy to human toxic nodular goiter suggest its value as an animal model for investigation of the pathophysiology and epidemiology of this disorder.