Thyroid Echogenicity Predicts Outcome of Radioiodine Therapy in Patients with Graves’ Disease

Abstract

Despite accounting for variations in gland size and iodine kinetics, the success of radioiodine therapy in patients with Graves' disease remains moderately common and unpredictable. We hypothesized that hypoechogenic glands, with large, densely packed cells, are more radiosensitive than normoechogenic glands, in which much radiation is wasted on more abundant colloid. We evaluated this hypothesis in a cohort of patients with Graves' disease. This was a prospective trial of patients recruited during 4 yr and followed up 1 yr after radioiodine therapy. This trial was held in a university hospital-outpatient clinic. A total of 177 consecutive patients with first presentation of Graves' disease (28 males), 23-76 yr old, who relapsed after antithyroid therapy were included in the study. The patients were assigned to an ablative target-absorbed dose of 200 Gy (n = 78) or randomly to 100 or 120 Gy of nonablative dose (n = 99). The measures were incidences of hyperthyroidism, euthyroidism, and hypothyroidism at 12-month follow-up. At follow-up there were 25 hyperthyroid, 44 euthyroid, and 108 hypothyroid patients. Compared with 96 patients with a hypoechogenic gland, in 81 patients with a normoechogenic gland, there were more hyperthyroid (22 vs. 7%) and euthyroid (41 vs. 11%), but less hypothyroid outcomes (37 vs. 81%; P < 0.0001). The other independent predictor of increased radioresistance was the large gland volume. In patients with Graves' disease, normoechogenic and large glands are associated with increased radioresistance.