Normalization of thyroid blood flow in Graves' hyperthyroidism following radioactive iodine therapy

In a group of 12 patients with Graves' hyperthyroidism, administration of 514 +/- 43 (mean +/- SD) MBq iodine-131 was associated with a fall of superior thyroid artery (STA) blood flow in two at 6 months and in eight at 11 months. The reduction in time-averaged velocity at 11 months correlated with the reduction in FT4 (r = 0.72, P less than 0.01) and in FT3 (r = 0.64, P less than 0.025) at this time. In four patients who had persistent elevated STA blood flow, two were still hyperthyroid. The diameter of the STA was unchanged at 6 months and only half the patients had reduction of their STA size at 11 months after radioiodine (RAI) therapy. These data indicate that normalization of STA blood flow precedes normalization of STA size in patients treated with RAI. Further work is required to determine whether STA blood flow measurements are of predictive value in treatment outcome.