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.