Journal of Korean Endocrine Society 1999;14(2):330-338.
Published online January 1, 2001.
Effect of Radioactive Iodine Therapy in Patients with Scan-Negative, Thyroglobulin-Positive Thyroid Cancer.
Eun Sook Kim, Seok Jun Hong, Jin Yub Kim, Young Ki Song, Jin Sook Ryu, Dae Hyuk Moon, Ki Soo Kim, Sang Wook Kim
Abstract
BACKGROUND
After total thyroidectomy the presence of detectable serum thyroglobulin(Tg) concentration is an index of residual or metastatic thyroid tissue and is usually well correlated with positive I whole body scan. However, it is not rare to find a patient with detectable serum Tg levels but without any uptake on I whole-body scan. At present it is not certain how to manage such patients. We performed whole body scan after administration of therapeutic dose of 131I to evaluate the usefulness of radioactive iodine therapy in the above setting. METHODS: Fifteen patients (4 males and 11 females, ranging in age from 17 to 74 years) were studied. They had been previously treated with total thyroidectomy for papillary thyroid cancer followed by therapy with 131I for ablation of their thyroid residue. Tg levels were determined by immunoradiometric assay method. 131I (100-200 mCi) therapy was administered and whole body scan was performed. 99mTc MIBI scans were taken in 9 patients. Follow up data of Tg were available in 12 patients at time interval of 6 12 months from the first study and treatment. RESULTS: Tg(on) levels of these patients were in a range of 2.2210 ng/mL (mean 36.1 +/- 59.1 ng/mL) and Tg(off) levels were 17.3 1,592 ng/mL (mean 197.3 +/- 400.3 ng/mL). After radioiodide therapy, Tg(on) levels were in 1.48.5 ng/mL (mean 11.0 +/- 13.5 ng/mL), Tg (off) were 11.9 478.0 ng/mL (mean 159.3 +/- 159.8 ng/mL). The Tg (on) levels were decreased significantly after RAI therapy, but Tg (off) levels had no significant difference, In 8 of the 15 patients (53.3%), posttreatment whole body scan showed definite positive uptakes which were not evident in pretreatment diagnostic scan. There were local recurrence in 3 cases, regional lymph node metastasis in 4 cases, and lung in I case. Diffuse hepatic uptake was definitely seen in 7 cases. The MIBI scan showed abnorml uptakes in 4 of 9 cases. CONCLUSION: The therapeutic usefulness of 100 to 200 mCi of 131I treatment in patients with 131I scan-negative and Tg-positive was unclear. And the MIBI scan was only partially effective. Further studies with other diagnostic and therapeutic approachs are required to evaluate the exact lesions and to improve prognosis.
Key Words: Differentiated thyroid carcinoma, Thyroglobulin-positive


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