Peer-reviewed veterinary case report
Why some hyperthyroid cats still have high thyroid after iodine
By Mullowney, Deirdre et al.·Published in Journal of veterinary internal medicine·2021·Department of Veterinary Clinical Sciences, United Kingdom·View original on PubMed →
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Original publication title: Treatment failure in hyperthyroid cats after radioiodine (I-131) injection.
- Species:
- cat
Plain-English summary
A group of 121 cats with hyperthyroidism were treated with radioactive iodine (I-131), but many still had high thyroid hormone levels after treatment. About 40% of the cats became normal without needing further treatment, but those with very high levels (over 150 nmol/L) were more likely to need additional help. For the cats that did need more treatment, options included medication, surgery, or repeat radioactive iodine treatment, which worked well for most of those who received it. If your cat's thyroid levels remain high after treatment, it may be worth discussing repeat treatment options with your vet.
People also search for: cat hyperthyroidism treatment failure · radioactive iodine for cats · cat thyroid surgery options
Abstract
BACKGROUND: There is limited published information on the outcome for cats where total thyroxine concentration (TT4) remains elevated after treatment with radioactive iodine (RAI). OBJECTIVE: To determine the frequency of, and predictors for, subsequent treatment failure in cats for which TT4 remains elevated at hospital discharge, and to report clinical outcomes for cats requiring repeat treatment. ANIMALS: One hundred twenty-one cats with TT4 ≥40 nmol/L after treatment with RAI (out of an original, treated study sample of 959 cats). METHODS: Retrospective study. Data regarding signalment, weight, TT4 concentration (before RAI treatment, at discharge, and percentage change), day of sampling, and I-131 dose were acquired. Logistic regression was performed to evaluate predictors of treatment failure. RESULTS: In the 87 cats for which classification was possible, 35 (40%) became euthyroid without further treatment. All TT4 variables and weight normalized RAI dose were independently predictive of subsequent treatment failure. In multivariate analysis, TT4 concentration at discharge (P < .001) and weight normalized RAI dose (P = .04) remained in the final model. All 28 cats with TT4 concentration ≥150 nmol/L at discharge ultimately failed treatment, compared with 13/40 (32.5%) and 11/19 (57.9%) cats with TT4 concentrations of 40-100 nmol/L and 100-150 nmol/L, respectively. Of the 52 cats that failed treatment, 14 were subsequently managed medically, 12 underwent thyroidectomy (4 with carcinoma), 14 had repeat RAI treatment which was successful in 12/14 (86%) cats, and 13 had no further treatment. CONCLUSIONS AND CLINICAL IMPORTANCE: Cats with TT4 >150 nmol/L at discharge after RAI might be candidates for immediate repeat treatment.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/33999452/