Changes in the Thyroid Technetium-99m Scintigram after Antithyroid and Subsequent Radioiodine Treatment for Solitary Autonomous Nodules

In patients with solitary autonomous thyroid nodules, the treatment of choice is radioiodine (¹³¹I) therapy, eventually preceded by antithyroid drugs to avoid aggravation of hyperthyroidism. The aim of this study was to evaluate the scintigraphical results of ¹³¹I treatment when using antithyroid pretreatment. Twenty-four patients having a solitary autonomous thyroid nodule were studied. A technetium-99m (^99mTc) pertechnetate scintigraphy was performed at the time of diagnosis, when serum thyrotropin (TSH) had been normal for about 3 months on antithyroid drug treatment, and finally when serum TSH was normalized after ¹³¹I treatment. The primary scintigram showed suppression of ^99mTc pertechnetate in the paranodular thyroid tissue in all patients. The second scintigram showed normal uptake in the paranodular tissue in 22 patients and a continuing suppression of the paranodular tissue in 2 patients. The third scintigram showed a solitary adenoma in 14 patients with none or almost no uptake in the paranodular tissue, resembling the first scintigram. In 6 patients an adenoma was still present, but uptake was seen in the paranodular tissue; in 3 patients a homogenous uptake without any sign of the previous nodule, and in 1 patient very low uptake in the gland was seen. Four patients developed hypothyroidism in the follow-up period of approximately 1 year. Pretreatment with antithyroid drugs induced an increase in serum TSH, stimulating the paranodular tissue. ¹³¹I will therefore be distributed in the whole thyroid gland, and not only in the autonomous solitary nodule. After ¹³¹I treatment, we continuously found a solitary nodule with low uptake in the paranodular tissue in 20 of 24 patients.