Compensated low-dose 131I therapy of Graves' disease.

To minimize the high rate of residual thyrotoxicosis encountered in low-dose 131I therapy of Graves' disease, we have treated 62 patients with a low-dose 131I protocol that includes a compensation for thyroid size. Dose varied between 40 muCi retained/g for glands of normal size to 100 muCi/g for glands of 100 g or greater. Mean dose was 51.9 muCi/g. At 1 year after therapy, 66.1% of subjects were euthyroid, 9.7% hypothyroid, and 24.2% hyperthyroid, a significant improvement (P less than 0.01) over our previous experience using 50 muCi/g independent of gland size. Several factors, other than 131I dose, which might influence the outcome of therapy, were investigated. Initial free thyroxine index observed before therapy was found to have prognostic significance. Hypothyroidism developed only in patients having an initial free thyroxine index of 22.5 or less (about 2.5 times the upper limit of normal in our laboratory).