Is empiric 131I therapy justified for patients with positive thyroglobulin and negative 131I whole-body scanning results?

Abstract

The long-term monitoring of patients with differentiated thyroid carcinoma (DTC) is essential throughout the patient's life after total or nearly total thyroidectomy followed by 131I remnant ablation and thyroid hormone suppression of thyroid-stimulating hormone (TSH). Sensitive surveillance for DTC recurrences and metastases includes radioiodine diagnostic whole-body scanning (DWBS) and measurement of serum thyroglobulin (Tg) levels after endogenous or exogenous TSH stimulation. Serum Tg levels during thyroid hormone withdrawal usually are correlated well with the results of DWBS. In general, Tg levels undetectable by DWBS suggest complete remission, whereas detectable or elevated Tg concentrations are suggestive of the presence of 131I uptake in local or distant metastases. However, DTC patients with a positive Tg test and negative 131I DWBS results (Tg+ DWBS-) have been observed in follow-up studies. The management of these cases begets controversy.

Methods: We electronically searched Medline (1966-2004.3), Embase (1984-2003), the Cochrane Library (2004, 2nd edition), CNKI (1994-2004), and CBM-DISC (1978-2004). We also manually searched the Chinese Journal of Isotopes, Radiologia pratica, and the Chinese Journal of Endocrinology and Metabolism.

Results: Ten serial observations and 3 nonrandomized controlled trials were found. The available data showed that of 314 patients who were treated empirically with 131I, 194 (62%) of 314 displayed pathologic uptake in the thyroid bed, lung, bone, mediastinum, and lymph nodes. In studies with Tg-on and Tg-off data, 171 (63%) of 271 patients achieved a decrease in Tg.

Conclusion: On the basis of data from recent studies, 131I therapy should be individualized according to clinical characteristics. More significantly, a decrease in Tg levels was achieved in 63% of DTC patients with Tg+ DWBS-, suggesting that 131I therapy does have a therapeutic effect when the Tg level is considered an index of tumor burden. The 62% positive posttherapy whole-body scanning results also indicated that a therapeutic dose of 131I could reveal approximately one half of previously undiagnosed lesions in some patients. Therefore, 131I therapy may be justified in patients with Tg levels of > 10 microg/L and DWBS- and who are at high risk of any recurrence.