Williams T, Elliott J, Syme H: Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism, J Vet Intern Med 24:1086, 2010.
Within 6 months of treatment of hyperthyroidism, 17-49% of cats develop azotemia. Treatment to restore euthyroidism in cats results in a decrease in renal glomerular filtration rate (GFR) which can lead to the development of azotemia if underlying chronic renal disease (CRD) is present. Antithyroid treatment could lead to iatrogenic hypothyroidism and hypothyroidism has been correlated with reduced GFR. The authors performed two retrospective studies. The first study was of 12 hyperthyroid cats treated with radioiodine and documented as euthyroid after treatment where changes were assessed in plasma thyroid stimulating hormone (TSH) concentration over a 6-month follow-up period. The second study was of 75 hyperthyroid cats, documented as euthyroid, that were monitored 6 months after starting treatment to identify the relationship between thyroid status and the development of azotemia. Plasma TSH concentrations were not suppressed in 7 of 8 cats with hypothyroidism 3 months after radioiodine treatment. The study concluded that cats with iatrogenic hypothyroidism were more likely to develop azotemia within 6 months after treatment for hyperthyroidism than cats defined as euthyroid. Hypothyroid cats with azotemia had shorter survival times than non-azotemic cats. There was no difference in survival times of euthyroid cats with or without azotemia. [VT]
Williams TL, Peak KJ, Brodbelt D et al: Survival and the development of azotemia after treatment of hyperthyroid cats, J Vet Intern Med 24:863, 2010.