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

Background: The aim of this work was to describe late permanent hypothyroid ism after iodine-131 or surgery, and to seek predictive factors of hypothyr oidism for the two treatments. Material: From 1979 to 1994, 462 patients with Graves' disease hyperthyroid ism underwent definitive treatment. Three hundred and fifty-five patients w ere treated with low calculated doses of iodine-131, and 107 patients with subtotal thyroidectomy. Life-table analysis was performed and the cumulativ e incidence of hypothyroidism was calculated by Kaplan-Meier's method, and survival (euthyroidism) within the groups was compared by the Mantel-Cox me thod. Results: Of the 355 patients treated with one dose of 6.6 +/- 1.9 mCi of io dine-131, 246 became euthyroid after one dose, and 109 needed 2 or more dos es. 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 ag e, 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 o f hyper thyroidism, duration of antithyroid treatment, weight of thyroid re sected, did not influence the final outcome. The weight of the thyroid remn ant 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. Conclusions: There is no ideal dose of iodine-131 that would correct hypert hyroidism in Graves' disease without risk of hypothyroidism. Surgery is an alternative definitive treatment with a risk of hypothyroidism within the 2 first years, an acumulative risk of hypothyroidism lower than with iodine- 131.