Effects of an Iodine-restricted Food on Hyperthyroidism in Client-owned Cats

Feline hyperthyroidism (Ht) is a common disease in middle-aged and elderly cats. Cur- rently, three treatment options are available: anti-thyroid medication, thyroidectomy and radioiodine therapy.

Recently, iodine-restricted foods were shown to be safe and effective in decreasing cir- culating total thyroxine (tt4) concentrations and manage feline Ht in a research colony of cats (1).

The objective of this study was to evaluate the effects of an iodine-restricted food* on circulating tt4 concentrations and clinical parameters in client-owned cats with Ht.

A prospective, multi-center, non-controlled, open-label study was performed. two hun- dred and twenty-five cats were enrolled in the study and transitioned to the iodine-re- stricted food*. Data from physical examinations, questionnaires completed by veterinar- ians and owners and plasma tt4, urea and creatinine concentrations were recorded at weeks 0, 4 and 8.

The study group included 136 female and 89 male cats (median age 15 years, range 4-21). one group had been on previous anti-thyroid medication (n=113) and the other group included newly diagnosed cats (n=112). plasma tt4 concentrations were signifi- cantly higher in the latter group at baseline (p=0.009), but at weeks 4 and 8, no signifi- cant differences were found between these groups. plasma tt4 concentrations decreased significantly to within the reference range at week 4 (p<0.001) and did not change significantly from week 4 to 8. Clinical parameters (vomiting, pu/pD, hyperactiv- ity, polyphagia, weight loss and hair coat quality) improved at 4 weeks (p<0.001). plasma urea and creatinine concentrations did not significantly change at any time point. a negative correlation was found between plasma tt4 concentrations and com- pliance at week 4 (p=0.015). the most common reason for dropout was poor palatabil- ity of the food.
In conclusion, in client-owned cats with Ht an iodine-restricted food is a valuable man- agement option to decrease plasma tt4 concentrations and improve clinical signs of Ht in 4-8 weeks. no short term side effects have been detected.

*Hill’sTM prescription DietTM y/dTM feline (containing on average 0.14 and 0.19 ppm iodine in the wet and dry forms, respectively)