Iatrogenic hypothyroidism in a hyperthyroid cat treated with 131I

Abstract

A thirteen-year-old, male, castrated, non-azotemic European Shorthair was presented for treatment of hyperthyroidism. Thyroid scintigraphy using Tc99m showed bilaterally enlarged thyroid glands with an increased thyroid to salivary (T/S) ratio. The cat was treated with an intravenous injection of 4.84 mCi (179MBa) 131I. One year later, the cat showed clinical deterio-ration, including lethargy, weight loss and a louder heart murmur; iatrogenic hypothyroidism was diagnosed. Concurrently, renal parameters were elevated compared to the pre-treatment values. Supplementation with levothyroxine was started. Four months later, the cat was euthyroid and improved creatinine values were noted. In this case report, the diagnosis and management of iatrogenic hypothyroidism in cats and the interplay with renal function are described. An algorithm with recommendations regarding diagnosis, monitoring and treatment of these cats is presented.