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| Feline HypertHyroidism: diagnosis & tHerapeutic modalities Long-Term Monitoring Once a euthyroid state is achieved, it is appropriate to continue patient monitoring indefinitely. • For stable patients without concurrent disease, evaluations (including T4) can take place every 6 months during the recommended wellness examination. • However, clinicians may schedule more frequent monitoring based on clinical judgment of individual patients/ owners. • Hyperthyroid cats with concurrent diseases generally should be evaluated at least every 3 to 4 months. IN SUMMARY Hyperthyroidism is the most common endocrine disease of older cats worldwide. While pathogenesis is unclear, several effective management options are available, including thyroidectomy, radioactive iodine therapy, and antithyroid medications. In addition, feeding a limited-iodine food is now an available option for management of hyperthyroid patients. All options should be discussed with pet owners to allow the best option to be selected for individual patients and their owners. n cKd = chronic kidney disease; dmB = dry matter basis; free thyroxine by equilibrium dialysis = ft4ed; gFr = glomerular filtration rate; gi = gastrointestinal; thyroxine = t4; tsH = thyroid-stimulating hormone References 1. Broussard JD, Peterson ME, Fox PR. Changes in clinical and laboratory findings in cats with hyperthyroidism from 1983 to 1993. JAVMA 1995; 206:302-305. 2. Peterson ME, Melian C, Nichols R. Measurement of serum concentrations of free thyroxine, total thyroxine, and total triiodothyronine in cats with hyperthyroidism and cats with nonthyroidal disease. JAVMA 2001; 218:529-536. 3. Peterson ME, Graves TK, Cavanagh I. Serum thyroid hormone concentrations fluctuate in cats with hyperthyroidism. J Vet Intern Med 1987; 1:142-146. 4. Wakeling J, Moore K, Elliott J, et al. Diagnosis of hyperthyroidism in cats with mild chronic kidney disease. J Small Anim Pract 2008; 49:287-294. 5. Peterson ME. Radioiodine for feline hyperthyroidism. In Bonagura JD,Twedt DC (eds): Kirk's Current Veterinary Therapy (Small Animal Practice). Philadelphia: Elsevier, 2008, pp 180-184. 6. Mooney CT. Hyperthyroidism. In Ettinger SJ, Feldman EC (eds): Textbook of Veterinary Internal Medicine. St. Louis: Elsevier, 2010, pp 1761-1779. 7. van Dijl IC, Hof AJ. Treatment of feline hyperthyroidism with radioactive iodine-131. Tijdschr Diergeneeskd 2008; 133:54-62. 8. Peterson ME, Becker DV. Radioiodine treatment of 524 cats with hyperthyroidism. JAVMA 1995; 207:1422-1428. 9. Theon AP, Van Vechten MK, Feldman E. Prospective randomized comparison of intravenous versus subcutaneous administration of radioiodine for treatment of hyperthyroidism in cats. Am J Vet Res 1994; 55:1734-1738. 10. Meric SM, Hawkins EC, Washabau RJ, et al. Serum thyroxine concentrations after radioactive iodine therapy in cats with hyperthyroidism. JAVMA 1986; 188:1038-1040. 11. Mooney CT. Radioactive iodine therapy in feline hyperthyroidism. Vet Rec 1990; 127:555. 12. Nykamp SG, Dykes NL, Zarfoss MK, et al. Association of the risk of development of hypothyroidism after iodine 131 treatment with the pretreatment pattern of sodium pertechnetate Tc 99m uptake in the thyroid gland in cats with hyperthyroidism: 165 cases (1990-2002). JAVMA 2005; 226:1671-1675. 13. Williams TL, Elliott J, Syme HM. Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism. J Vet Intern Med 2010; 24:1086-1092. 14. Hill KE, Gieseg MA, Kingsbury D, et al. The efficacy and safety of a novel lipophilic formulation of methimazole for the once daily transdermal treatment of cats with hyperthyroidism. J Vet Intern Med 2011; 25:1357-1365. 15. Peterson ME, Kintzer PP, Hurvitz AI. Methimazole treatment of 262 cats with hyperthyroidism. J Vet Intern Med 1988; 2:150-157. 16. Sartor LL, Trepanier LA, Kroll MM, et al. 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Wedekind KJ, Kirk CA, Nachreiner R. Methods for preventing feline hyperthyroidism in a cat and composition comprising limited iodine. World Intellectual Property Organization, 2004, pp 1-29. 29. Ranz D, Tetrick M, Opitz B, et al. Estimation of iodine status in cats. J Nutrition 2002; 132:S1751-S1753. 30. Boag AK, Neiger R, Slater L, et al. Changes in the glomerular filtration rate of 27 cats with hyperthyroidism after treatment with radioactive iodine. Vet Rec 2007; 161:711-715. 31. Adams WH, Daniel GB, Legendre AM. Investigation of the effects of hyperthyroidism on renal function in the cat. Can J Vet Res 1997; 61:53-56. 32. Adams WH, Daniel GB, Legendre AM, et al. Changes in renal function in cats following treatment of hyperthyroidism using 131I. Vet Radiol Ultrasound 1997; 38:231-238. 33. Graves TK, Olivier NB, Nachreiner RF, et al. Changes in renal function associated with treatment of hyperthyroidism in cats. Am J Vet Res 1994; 55:1745-1749. 34. Elliott J, Rawlings JM, Markwell PJ, et al. Survival of cats with naturally occurring chronic renal failure: Effect of dietary management. J Small Anim Pract 2000; 41:235-242. 35. Ross SJ, Osborne CA, Kirk CA, et al. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. JAVMA 2006; 229:949-957. 36. Becker TJ, Graves TK, Kruger JM, et al. Effects of methimazole on renal function in cats with hyperthyroidism. JAVMA 2000; 36:215-223. 37. Williams TL, Peak KJ, Brodbelt D, et al. Survival and the development of azotemia after treatment of hyperthyroid cats. J Vet Intern Med 2010; 24:863-869. 38. Williams TL, Elliott J, Syme HM. Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism. J Vet Intern Med 2010; 24:1086-1092. 39. Wakeling J, Rob C, Elliott J, et al. Survival of hyperthyroid cats is not affected by post-treatment azotemia. ECVIM-CA Congress Proc, 2006, p 1523. David Bruyette, DVM, Diplomate ACVIM, is the medical director at West Los Angeles Animal Hospital and a clinical professor in the Department of Radiation Oncology at University of California—Los Angeles. Prior to his current positions, he was an assistant professor and head of internal medicine at Kansas State University and director of its Analytical Chemistry Laboratory. Dr. Bruyette received his DVM from University of Missouri and completed an internship at Purdue University and residency in internal medicine at University of California—Davis. He then became a staff internist at West Los Angeles Veterinary Medical Group and member of the Department of Comparative Medicine at Stanford University.