Outcome following radioactive iodine therapy in Graves' disease

One hundred and fifty three patients with Graves' hyperthyroidism treated with I-131 from March 1984 to September 1988 were analyzed. The dose of I-131 was given according to the formula: 100 microCi/gm x estimated thyroid size (gm) x 100/24 hr I-131 uptake (%) The mean dose was 5.41 mCi and the maximum dose was 7 mCi. After one year of follow up, 45 patients (29.4%) were euthyroid, 35 patients (22.9%) became hypothyroid, and 73 patients (47.7%) were persistently hyperthyroid. Discriminant analysis of pretreatment variables suggested that those patients who were still hyperthyroid at the end of the first year had significantly larger goiter size, and higher serum T4 and T3 levels. Men had greater incidence of relapse. Besides, those who had received antithyroid drug before I-131 therapy had a significantly higher incidence of failure. As compared with previous studies, our report had a significantly higher incidence (22.9%) of hypothyroidism one year after I-131 therapy, which may be due to recognition of subclinical hypothyroidism through TSH assay.