Peer-reviewed veterinary case report
Survival of hyperthyroid cats after radioiodine and thyroid treatment
By Cox, Sarah E et al.·Published in Journal of veterinary internal medicine·2025·Department of Veterinary Medicine, United Kingdom·View original on PubMed →
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Original publication title: Survival of radioiodine treated hyperthyroid cats that are euthyroid and hypothyroid after treatment, and effect of levothyroxine supplementation on survival time of cats with iatrogenic hypothyroidism.
- Species:
- cat
Plain-English summary
A group of 117 cats treated for hyperthyroidism with radioiodine were studied to see how their thyroid hormone levels affected their survival. Cats that became hypothyroid (low thyroid hormone) after treatment had shorter lifespans unless they received levothyroxine (a thyroid hormone supplement). Those nonazotemic (not suffering from kidney issues) hypothyroid cats that were given levothyroxine lived longer than those who did not receive the supplement. However, the treatment did not seem to help hypothyroid cats with kidney problems. Overall, levothyroxine can improve survival in certain cats after hyperthyroid treatment.
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Abstract
BACKGROUND: Hyperthyroid cats that are azotemic and hypothyroid after surgical or medical treatment have poor outcomes, and supplementation with levothyroxine (LT4) improves survival. However, the effect of LT4 supplementation on survival of nonazotemic, hypothyroid radioiodine (RI)-treated hyperthyroid cats is unknown. HYPOTHESIS: Radioiodine treated hyperthyroid cats with iatrogenic hypothyroidism or azotemia have shorter survival times than euthyroid, nonazotemic cats and supplementation of LT4 improves survival times of hypothyroid cats. ANIMALS: One hundred seventeen RI treated hyperthyroid cats. METHODS: Prospective cohort study. Radioiodine treated cats were screened for azotemia and iatrogenic hypothyroidism using TSH stimulation test; LT4 supplementation was offered to all hypothyroid cats with decision to treat based on owner preference. The log rank test was used to compare survival times between groups, and the Mann-Whitney U test was used to compare age and renal variables. Data are presented as median [range]. RESULTS: Euthyroid azotemic cats (934 [759-2035] days) and nonsupplemented hypothyroid cats (azotemic and nonazotemic combined, 1232 [238-2363] days) had shorter survival times than euthyroid nonazotemic cats (1616 [663-3369] days, P = .003 and P = .002, respectively). Levothyroxine supplemented hypothyroid nonazotemic cats had longer survival times than nonsupplemented hypothyroid nonazotemic cats (1037 [300-2401] days vs 768 [34-1014] days; P = .027). Levothyroxine supplementation was not associated with prolonged survival times in hypothyroid azotemic cats vs nonsupplemented hypothyroid azotemic cats (771 [718-1558] days vs 152 [82-1852] days, respectively, P = .991). CONCLUSIONS AND CLINICAL IMPORTANCE: Levothyroxine supplementation in nonazotemic cats with iatrogenic hypothyroidism (diagnosed based on TSH stimulation test results) improved survival times, although randomized controlled trials are needed.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/39831449/