Treatment Options and Considerations for Hyperthyroid Cats

The underlying cause of the thyroid tumors (adenomatous hyperpla­sia, adenoma, or carcinoma) associated with feline hyperthyroidism is not known. Because sponta­neous remission of hyperthyroidism in cats does not occur, the aim of treatment is to control the excessive secretion of thyroid hormone from the adenomatous thyroid gland.

The 4 Treatment Options 

In cats, hyper­thyroidism can be treated in four ways — surgical thyroidectomy, radioactive io­dine (131-I), chronic administration of an antithy­roid drug, or lifelong feeding of an ultra-low iodine diet. Each form of treatment has advantages and disadvantages, which must be considered when formulating the best treatment plan for the individual hyperthyroid cat.

Formulating the Best Form of Treatment for Each Cat

The treatment of choice for an individual cat depends on several factors, including the age of the cat, presence of associated cardiovascular dis­eases or other major medical problems (e.g., chronic kidney disease), availability of a skilled surgeon or radioiodine treatment facility, and owner's preference.

The cost of therapy is a major consideration for many cat owners. Medical treatment or use of low-iodine dietary therapy costs far less initially. However, the cost of ongoing monitoring can exceed that of thyroidectomy or radioiodine therapy over a period of many months to years.

Cure versus Control of Hyperthyroidism

Of the four forms of treatment avail­able, it must be emphasized that only surgery and radioactive iodine remove and destroy the thyroid tumors, respectively, and thereby "cure" the hyper­thyroid state.

Use of an antithyroid drug (e.g., methimazole or carbimazole) will block thyroid hormone synthesis. And chronic feeding of an iodine deficient diet will reduce the production of T4 and T3 by the thyroid tumor. However, because antithyroid drugs and low-iodine diets do not de­stroy the hyperthyroid cat’s thyroid tumor(s), hyperthyroidism will recur once antithyroid drugs or dietary therapy is discontinued.

Outline of Treatment

Over the next few weeks, I’ll be discussing each of the four treatment options for hyperthyroidism in some detail. In my next post, however, l will review a frequently neglected but very important part of any of the treatment options — that is, providing the hyperthyroid cat with proper nutrition and adequate amounts of water.

Hyperthyroid cats develop many muscle wasting as well as many metabolic complications because of their disease. Therefore, they have special dietary needs and require a high-quality nutrients in their daily diet including adequate amounts of water, protein, fat, vitamins, and minerals.

References

1. Birchard SJ, Peterson ME, Jacobson A:  Surgical treatment of feline hy­perthyroidism:  Results of 85 cases.  Journal of the American Animal Hospital Association 1984;20:705-709.
2. Peterson ME, Kintzer PP, Hurvitz AI: Methimazole treatment of 262 cats with hyper­thyroidism. Journal of Veterinary Internal Medicine 1988;2:150-157.
3. Welches CD, Scavelli TD, Matthiesen DT, Peterson ME: Occurrence of problems after three techniques of bilateral thyroidectomy in cats. Veterinary Surgery 1989;18:392-396.
4. Peterson ME, Becker DV: Radioiodine treatment of 524 cats with hyperthyroidism. Journal of the American Veterinary Medical Association  1995;207:1422-1428.
5. Peterson ME: Radioiodine treatment for hyperthyroidism. Clinical Techniques in Small Animal Practice 21:34-39, 2006
6. Peterson ME: Hyperthyroidism, In: Ettinger SJ, Feldman EC (eds): Textbook of Veterinary Internal Medicine: Diseases of the Dog and Cat (Fifth Edition). Philadelphia, WB Saunders Co. 2000; pp 1400-1419.
7. Peterson ME: Hyperthyroidism in cats. In: Melian C (ed): Manual de Endocrinología en Pequeños Animales (Manual of Small Animal Endocrinology). Multimedica, Barcelona, Spain, 2008, pp 127-168.
8. Peterson ME: Radioiodine for hyperthyroidism. In: Bonagura JD, Twedt DC  (eds): Current Veterinary Therapy XIIII.  Philadelphia, Saunders Elsevier, 2009, pp 180-184.
9. Mooney CT, Peterson ME: Feline hyperthyroidism, In: Mooney C.T., Peterson M.E. (eds), Manual of Canine and Feline Endocrinology (Fourth Ed), Quedgeley, Gloucester, British Small Animal Veterinary Association, 2012; in press
10. Baral R, Peterson ME: Thyroid Diseases, In: Little, S. (ed), The Cat: Clinical Medicine and Management. Philadelphia, Elsevier Saunders, 2012; in press.
11. Peterson ME: Hyperthyroidism in cats, In: Rand, J (ed), Clinical Endocrinology of Companion Animals. New York, Wiley-Blackwell, 2012; in press.