Predicting outcomes in hyperthyroid cats treated with radioiodine

Abstract

Background: Radioiodine (131I) is the treatment of choice for cats with hyperthyroidism. After 131I, however, euthyroidism is not always achieved, with 5% to 10% of cats remaining persistently hyperthyroid and 20% to 50% developing iatrogenic hypothyroidism. Objectives: To identify pretreatment factors that may help predict persistent hyperthyroidism and iatrogenic hypothyroidism after treatment of cats using a novel 131I dosing algorithm. Animals: One thousand and four hundred hyperthyroid cats treated with 131I. Methods: Prospective, before-and-after study. Pretreatment predictors (clinical, laboratory, scintigraphic, 131I dose, 131I uptake measurements) of treatment failure or iatrogenic hypothyroidism were identified by multivariable logistic regression analysis. Results: Cats that developed iatrogenic hypothyroidism were more likely to be older (odds ratio [OR] = 1.10; 95% confidence interval [CI], 1.04-1.17; P =.001), female (OR = 2.04; 95% CI, 1.54-2.70; P