Utility of fluorine-18-fluorodeoxyglucose positron emission tomography in differentiated thyroid carcinoma with negative radioiodine scans and elevated serum thyroglobulin levels

BACKGROUND: This study aimed to determine the role of fluorine-18-fluorodeo xyglucose positron emission tomography (FDG-PET) in the follow-up of patien ts who underwent total thyroidectomy and iodine-131 (I-131) ablation therap y for differentiated thyroid cancer and presented increased thyroglobulin l evels with negative I-131 and thallium-201 (Tl-201) scans. METHODS: Two patients with follicular carcinoma and eight with papillary tu mors underwent total thyroidectomy and I-131 therapy until the I-131 scan w as negative. I-131 and Tl-201 scans were performed with negative results in all cases, while serum thyroglobulin measurements were all positive with n egative thyroglobulin autoantibodies. One week after the I-131 scans, all t he patients underwent FDG-PET whole-body scans. RESULTS: The FDG-PET scan detected in 4 patients, a single focal increase o f FDG uptake in one lymph node metastasis (subsequently confirmed histologi cally); in 1 patient, multiple pathological focal uptakes in brain, neck, a nd chest; and in 1 patient, two mild focal uptakes in the mediastinum, clos e to the tracheal branch, In 2 other patients, pathological FDG uptakes in cervical spine and mediastinum were not confirmed by other imaging techniqu es, and in the 2 remaining patients the scan results were inconclusive. The sensitivity of FDG-PET whole-body scan for detecting metastatic thyroid ca ncer was 60%. CONCLUSIONS: This study indicates that the FDG-PET whole-body scan is a use ful tool in the follow-up of patients with differentiated thyroid cancer, n egative I-131 and Tl-201 scans and elevated serum thyroglobulin levels. The FDG-PET scan detects metastatic disease in 60% of patients with differenti ated thyroid cancer, enabling surgical therapy to be performed on accessibl e lesions. (C) 2000 by Excerpta Medica, Inc.