ABSTRACT
BACKGROUND: In patients with differentiated thyroid cancer treated by surgery and radioactive iodine ablation, serum thyroglobulin(Tg) and 131I whole body scan(WBS) are recognized as being the best cooperative indicators for detection of recurrence or metastasis. However, in some cases, 131I WBS shows no specific lesions despite elevated serum Tg. Therefore, 18-Fluorine-fluorodeoxyglucose (FDG) positron emission tomography(PET) has emerged as a useful method for the detection of 131I WBS negative thyroid cancers. The aims of the present study are to evaluate the clinical usefulness of this technique in detection and to compare the results with 99mTc-MIBI scintigraphy(MIBI) in cases of final results being confirmed by histologic diagnosis and other imaging methods. METHODS: We conducted a retrospective analysis amon 131I WBS negative recurred papillary thyroid carcinoma patients(male: female ratio=9:22, median age=42 yr). FDG PET was performed in 28 patients and MIBI 28 patients, 25 of whom were common to both groups. All patients had histologically proven recurrence/metastasis and negative 131I WBS results but persistently elevated serum Tg levels. In each case overall clinical evaluations were performed including histology, cytology, thyroglobulin level, other imaging methods, posttherapy 131I WBS and subsequent clinical course, to allow comparison with the results of FDG PET. RESULTS: In 19 cases of patients with negative 131I WBS, proven recurrence/metastasis lesions were detected in FDG PET. Compared with MIBI, FDG PET was found to be superior in 8 cases(including 2 patients with distant metastases). No FDG-negative/MIBI-positive tumor was observed. One FDG PET negative and MIBI negative case was proven 3 months later to be metastatic cervical lymph nodes, Sensitivities were 94.7% in the FDG PET group and 52.6% in MIBI. Diagnostic accuracy of FDG PET was superior to that of MIBI(93% vs. 62%, respectively, p=0.003). CONCLUSION: Our results confirmed the clinical usefulness of FDG PET for detection of 131I negative differentiated thyroid cancers and suggested the value of FDG PET as an initial diagnostic step, rather than MIBI, in these cases.