Effect of Feeding an Iodine-Restricted Diet in Cats with Spontaneous Hyperthyroidism

BackgroundExclusive feeding of an iodine-restricted diet has been proposed as a method for controlling clinical manifestations of hyperthyroidism in hyperthyroid cats. ObjectivesTo determine the effect of feeding an iodine-restricted diet on TT4 concentrations and clinical signs in cats with spontaneous hyperthyroidism. AnimalsForty-nine client-owned cats with spontaneous hyperthyroidism. MethodsRetrospective case series. Hyperthyroid cats were exclusively fed a commercially available iodine-restricted diet. Clinical response was assessed by change in weight and heart rate and serum TT4, blood urea nitrogen (BUN), and creatinine concentrations at various times during dietary management (21-60days, 60-180days). ResultsSerum TT4 normalized in 20/48 cats (42%) and 39/47 cats (83%) at 21-60days and 61-180days, respectively. Cats in which the TT4 concentrations were still above reference range at 21-60days had a significantly higher starting TT4 than those that normalized their TT4 levels during the same time period (P=.038). Body weight did not significantly increase (P=.34) nor heart rate decrease (P=.64) during the study. There was a significant decrease in serum creatinine (P=.028). Cats in the low reference range for serum TT4 concentrations did not have a significant increase in body weight (P=.41) nor creatinine (P=.54) when compared to those with high reference range. Conclusions and Clinical ImportanceRestricted-iodine diets were effective at maintaining serum TT4 concentrations within reference ranges for a majority of cats with spontaneous hyperthyroidism over 1year, although not all clinical signs of hyperthyroidism improved.