Results of this study were presented at the ACVIM Forum, Anaheim, CA, 2010.
Association of Iatrogenic Hypothyroidism with Azotemia and Reduced Survival Time in Cats Treated for Hyperthyroidism
Article first published online: 2 AUG 2010
Copyright © 2010 by the American College of Veterinary Internal Medicine
Journal of Veterinary Internal Medicine
Volume 24, Issue 5, pages 1086–1092, September/October 2010
How to Cite
Williams, T.L., Elliott, J. and Syme, H.M. (2010), Association of Iatrogenic Hypothyroidism with Azotemia and Reduced Survival Time in Cats Treated for Hyperthyroidism. Journal of Veterinary Internal Medicine, 24: 1086–1092. doi: 10.1111/j.1939-1676.2010.0566.x
- Issue published online: 2 SEP 2010
- Article first published online: 2 AUG 2010
- Submitted February 3, 2010; Revised April 20, 2010; Accepted June 6, 2010.
- Euthyroid-sick syndrome;
- Subclinical hypothyroidism;
- Thyroid stimulating hormone
Background: Iatrogenic hypothyroidism can occur after treatment of hyperthyroidism, and is correlated with a reduced glomerular filtration rate in humans and dogs.
Hypothesis: Cats with iatrogenic hypothyroidism after treatment for hyperthyroidism will have a greater incidence of azotemia than euthyroid cats.
Animals: Eighty client owned cats with hyperthyroidism.
Methods: Two retrospective studies. (1) Longitudinal study of 12 hyperthyroid cats treated with radioiodine (documented as euthyroid after treatment), to assess changes in plasma thyroid stimulating hormone (TSH) concentration over a 6-month follow-up period, (2) Cross-sectional study of 75 hyperthyroid cats (documented as euthyroid) 6 months after commencement of treatment for hyperthyroidism to identify the relationship between thyroid status and the development of azotemia. Kaplan-Meier survival analysis was performed to identify relationships between thyroid and renal status and survival.
Results: Plasma TSH concentrations were not suppressed in 7 of 8 cats with hypothyroidism 3 months after radioiodine treatment. The proportion of cats with azotemia was significantly (P= .028) greater in the hypothyroid (16 of 28) than the euthyroid group (14 of 47). Twenty-eight of 41 cats (68%) with plasma TT4 concentration below the laboratory reference range had an increased plasma TSH concentration. Hypothyroid cats that developed azotemia within the follow-up period had significantly (P= .018) shorter survival times (median survival time 456 days, range 231–1589 days) than those that remained nonazotemic (median survival time 905 days, range 316–1869 days).
Conclusions and Clinical Importance: Iatrogenic hypothyroidism appears to contribute to the development of azotemia after treatment of hyperthyroidism, and reduced survival time in azotemic cats.