Long-term follow-up studies on iodine-131 treatment of hyperthyroid Graves' disease based on the measurement of thyroid volume by ultrasonography.

In the present series of studies, the long-term (four year) effect of 80 Gy of 131I treatment was evaluated in patients with hyperthyroid Graves' disease whose thyroid volumes have been accurately estimated with a high resolution ultrasound scanner. One year after 131I treatment, 23.1% (3 out of 13 patients) remained hyperthyroid, 69.2% (9 out of 13) became euthyroid, and 7.7% (1 out of 13) were in a hypothyroid state. Since three patients in a hyperthyroid state one year after treatment were subsequently treated with either antithyroid drugs or additional 131I treatment, the remaining ten patients (9 euthyroid and 1 hypothyroid patients) have been followed up for three more years. Two patients developed a hypothyroid state three years after treatment and one patient four years after treatment. Overall, 60% (6 out of 10 patients) were in a euthyroid state and 40% (4 out of 10) in a hypothyroid state, four years after 80 Gy 131I treatment. There was no significant difference between eu- and hypothyroid groups in the sex ratio, age, radiation dose, therapeutic dose, thyroid gland volume, 24-hr 131I uptake, the effective half-life of 131I in the thyroid or the duration of hyperthyroidism. In our preliminary studies, the incidence of late hypothyroidism in our 131I treatment is similar to those previously reported. These suggest that uncertain factor(s), such as inhomogeneity of iodine distribution in the thyroid, unequal sensitivity of the thyroid cells to the radiation, and/or persistent destructive effects of the autoimmune process may influence the long-term effect of 131I treatment of Graves' disease.