Open AccessPredicting outcomes in hyperthyroid cats treated with radioiodine
Author(s) -
Peterson Mark E.,
Rishniw Mark
Publication year - 2021
Publication title -
journal of veterinary internal medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.356
H-Index - 103
eISSN - 1939-1676
pISSN - 0891-6640
DOI - 10.1111/jvim.16319
Subject(s) - medicine , cats , confidence interval , odds ratio , gastroenterology , prospective cohort study , logistic regression , thyroid , radioactive iodine , iodine , endocrinology , materials science , metallurgy
Background Radioiodine ( 131 I) is the treatment of choice for cats with hyperthyroidism. After 131 I, however, euthyroidism is not always achieved, with 5% to 10% of cats remaining persistently hyperthyroid and 20% to 50% developing iatrogenic hypothyroidism. Objectives To identify pretreatment factors that may help predict persistent hyperthyroidism and iatrogenic hypothyroidism after treatment of cats using a novel 131 I dosing algorithm. Animals One thousand and four hundred hyperthyroid cats treated with 131 I. Methods Prospective, before‐and‐after study. Pretreatment predictors (clinical, laboratory, scintigraphic, 131 I dose, 131 I uptake measurements) of treatment failure or iatrogenic hypothyroidism were identified by multivariable logistic regression analysis. Results Cats that developed iatrogenic hypothyroidism were more likely to be older (odds ratio [OR] = 1.10; 95% confidence interval [CI], 1.04‐1.17; P = .001), female (OR = 2.04; 95% CI, 1.54‐2.70; P < .001), have detectable serum thyroid‐stimulating hormone (TSH) concentrations (OR = 4.19; 95% CI, 2.0‐8.81; P < .001), have bilateral thyroid nodules (OR = 1.57; 95% CI, 1.19‐2.08; P < .001), have homogeneous, bilateral distribution of 99m Tc‐pertechnetate uptake (OR = 2.93; 95% CI, 2.05‐4.19; P < .001), have milder severity score (OR = 0.62; 95% CI, 0.49‐0.79; P < .001), and have higher 131 I uptake (OR = 2.40; 95% CI, 1.75‐3.28; P < .001). In contrast, cats remaining persistently hyperthyroid were more likely to be younger (OR = 0.81; 95% CI, 0.72‐0.92; P < .001), have higher severity score (OR = 1.87; 95% CI, 1.51‐2.31; P < .001), and have lower 131 I uptake (OR = 3.50; 95% CI, 1.8‐6.80; P < .001). Conclusions and Clinical Importance Age, sex, serum TSH concentration, bilateral and homogeneous 99m Tc‐pertechnetate uptake on scintigraphy, severity score, and percent 131 I uptake are all factors that might help predict outcome of 131 I treatment in hyperthyroid cats. Cats with persistent hyperthyroidism had many predictive factors that directly contrasted those of cats that developed 131 I‐induced hypothyroidism.