Antithyroid Drug Treatment Can Induce Remission of Hyperthyroidism in Humans But Not Cats

In humans, Graves' disease is the most common cause of hyperthyroidism in both adults and children (1). Graves' Disease is caused by the patient's immune system producing an antibody that attacks and turns on the thyroid.

One of the goals of treating patients with antithyroid medications is the hope that these drugs may cause the immune system to stop producing the antibody, resulting in the Graves' Disease going into remission (1). In a recent study of children with Graves' disease, up to 50% of these young patients experienced remission of their hyperthyroidism (2).

This is completely different than the situation we see in cats with hyperthyroidism. Cats do not develop Graves' Disease (3-8). Rather, hyperthyroidism in cats is caused by one or more thyroid tumors (see my blog post, Do All Hyperthyroid Cats Have a Thyroid Tumor?). These thyroid tumors are generally benign (adenomas) but can rarely become malignant.

Although cats frequently are treated for prolonged periods with antithyroid drugs to lower their high circulating thyroid levels and manage their hyperthyroidism, these cats will never go into remission (5-9). For more information on the advantages and disadvantages of using antithyroid drugs in hyperthyroid cats, see my blog post, Treating Cats with Hyperthyroidism: Antithyroid Drugs).

References

1. Cooper DS. Antithyroid drugs. New England Journal of Medicine 2005;352:905-917.
2. Léger J, Gelwane G, Kaguelidou F, French Childhood Graves' Disease Study Group. Positive impact of long-term antithyroid drug treatment on the outcome of children with Graves' disease: national long-term cohort study. Journal of Clinical Endocrinology and Metabolism 2012;97:110-119. (summarized here in Clinical Thyroidology for Patients).
3. Gerber H, Peter H, Ferguson DC, et al. Etiopathology of feline toxic nodular goiter. Veterinary Clinics of North America Small Animal Practice 1994;24:541-565.
4. Peterson ME, Ward CR. Etiopathologic findings of hyperthyroidism in cats. Veterinary Clinics of North America Small Animal Practice 2007;37:633-645.
5. Peterson ME: Hyperthyroidism in cats. In: Melian C (ed): Manual de Endocrinología en Pequeños Animales (Manual of Small Animal Endocrinology). Barcelona, Multimedica, 2008; 127-168.
6. Baral R, Peterson ME. Thyroid gland disorders. In: Little, S.E. (ed), The Cat: Clinical Medicine and Management. Philadelphia, Elsevier Saunders 2012; 571-592.
7. 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;92-110.
8. Peterson ME: Hyperthyroidism in cats, In: Rand, J (ed), Clinical Endocrinology of Companion Animals. New York, Wiley-Blackwell, 2012; in press.
9. Peterson ME, Kintzer PP, Hurvitz AI. Methimazole treatment of 262 cats with hyperthyroidism. Journal of Veterinary Internal Medicine 1988;2:150–157.