Kidney Insufficiency After Treatment for Feline Hyperthyroidism

Riensche, M. R., T. K. Graves, et al. (2008). "An investigation of predictors of renal insufficiency following treatment of hyperthyroidism in cats." J Feline Med Surg 10(2): 160-6.

Renal insufficiency is a common finding in older cats, affecting about 30% of cats over age 15. Hyperthyroidism is the most common endocrine disorder in cats, and it appears to be increasing in incidence over time. Hyperthyroidism can mask underlying renal disease by causing an increase in the glomerular filtration rate (GFR). Treatment of hyperthyroidism leads to a decrease in GFR and an increase in blood urea nitrogen (BUN). Different treatments exist for hyperthyroidism in cats, including reversible (methimazole) and irreversible (thyroidectomy, radioiodine) options. The ability to predict which cats will develop renal insufficiency after treatment for hyperthyroidism would help guide treatment decisions. The purpose of this retrospective study was to determine if routine pre-treatment clinical data can be used to predict the development of overt renal insufficiency following treatment of feline hyperthyroidism. Medical records were reviewed for 39 nonazotemic cats undergoing treatment for hyperthyroidism at the College of Veterinary Medicine, University of Illinois. The records were reviewed for for signalment, clinical signs, and serum biochemical, hematologic and urinalysis findings before and after treatment for hyperthyroidism. Cats that developed renal insufficiency within 6 months after treatment (n=20) were compared to cats that did not (n=19). No significant differences could be detected between the groups with respect to the parameters measured. The study suggests that the results of routine pre-treatment clinical data cannot be used to predict renal function after treatment for hyperthyroidism, and that a trial of methimazole therapy is indicated before choosing irreversible treatment such as radioiodine.
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Related articles:
Boag, A. K., R. Neiger, et al. (2007). "Changes in the glomerular filtration rate of 27 cats with hyperthyroidism after treatment with radioactive iodine." Vet Rec 161(21): 711-5.
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