Hypothyroidism after iodine-131 or surgical therapy for Graves' disease hyperthyroidism

The aim of this work was to describe late permanent hypothyroidism after iodine-131 or surgery, and to seek predictive factors of hypothyroidism for the two treatments.

From 1979 to 1994, 462 patients with Graves' disease hyperthyroidism underwent definitive treatment. Three hundred and fifty-five patients were treated with low calculated doses of iodine-131, and 107 patients with subtotal thyroidectomy. Life-table analysis was performed and the cumulative incidence of hypothyroidism was calculated by Kaplan-Meier's method, and survival (euthyroidism) within the groups was compared by the Mantel-Cox method.

Of the 355 patients treated with one dose of 6.6 1.9 mCi of iodine-131, 246 became euthyroid after one dose, and 109 needed 2 or more doses. Twenty-two patients received one or more doses higher than 10 mCi. The probability of euthyroidism at 145 months after low-dose was 10. 19% and age, sex, pretreatment with antithyroid drugs, previous subtotal surgery did not influence the final outcome. Of the 107 surgically treated patients the probability of euthyroidism at 144 months was 56.1%. Age, sex, duration of hyperthyroidism, duration of antithyroid treatment, weight of thyroid resected, did not influence the final outcome. The weight of the thyroid remnant was 5.4 1.5 g and the multivariate statistical model by conditional logistic regression showed that the weight of thyroid remnant was the only variable that influenced long-term thyroid function.

There is no ideal dose of iodine-131 that would correct hyperthyroidism in Graveś disease without risk of hypothyroidism. Surgery is an alternative definitive treatment with a risk of hypothyroidism within the 2 first years, and a cumulative risk of hypothyroidism lower than with iodine-131.