Source: J Vet Intern Med. 2022 Jan-Feb; 36(1): 49–58.

doi: 10.1111/jvim.16319.


Hyperthyroidism is a common disease in cats, and mostly afflicts cats middle-aged and older. It is caused by the overproduction of thyroid hormone by the thyroid glands. Radioiodine (131 I) is the treatment of choice to restore euthyroidism with a single dose of radiation without producing hypothyroidism for cats receiving the treatment. However, 30% to 50% of 131I‐treated cats develop iatrogenic hypothyroidism after treatment. Besides, 5% to 10% of hyperthyroid cats fail 131I treatment and remain persistently hyperthyroid.


To identify pretreatment factors that may help predict persistent hyperthyroidism and iatrogenic hypothyroidism after treatment of cats using a novel 131I dosing algorithm. Peterson, ME and Rishniw, M conducted a study involving one thousand and four hundred hyperthyroid cats treated with 131I. Cats underwent an evaluation that included a complete physical examination, routine laboratory testing (CBC, serum biochemical profile, complete urinalysis), determination of serum thyroid hormone concentrations (total thyroxine [T4], triiodothyronine [T3], and thyroid‐stimulating hormone [TSH]), and qualitative and quantitative thyroid scintigraphy.


Pretreatment predictors (clinical, laboratory, scintigraphic, 131I dose, 131I uptake measurements) of treatment failure or iatrogenic hypothyroidism were identified by multivariable logistic regression analysis. In conclusion, Age, sex, serum TSH concentration, bilateral and homogeneous 99mTc‐pertechnetate uptake on scintigraphy, severity score, and percent 131I uptake are all factors that might help predict outcome of 131I treatment in hyperthyroid cats.


Forest plots showing odds ratio and 95% CI of pretreatment factors contributing to persistent hyperthyroidism (treatment failure). Multivariable logistic regression indicated the following 3 predictors: younger age; bilateral thyroid disease; higher 131I severity score; and low 131I thyroid uptake (<16%). CI, confidence interval

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