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-fluorodeoxyglucose positron emission tomography (FDG-PET) in the follow-up of patients who underwent total thyroidectomy and iodine-131 ((131)I) ablation therapy for differentiated thyroid cancer and presented increased thyroglobulin levels with negative (131)I and thallium-201 ((201)Tl) scans.

METHODS: Two patients with follicular carcinoma and eight with papillary tumors underwent total thyroidectomy and (131)I therapy until the (131)I scan was negative. (131)I and (201)Tl scans were performed with negative results in all cases, while serum thyroglobulin measurements were all positive with negative thyroglobulin autoantibodies. One week after the (131)I scans, all the patients underwent FDG-PET whole-body scans.

RESULTS: The FDG-PET scan detected in 4 patients, a single focal increase of FDG uptake in one lymph node metastasis (subsequently confirmed histologically); in 1 patient, multiple pathological focal uptakes in brain, neck, and chest; and in 1 patient, two mild focal uptakes in the mediastinum, close to the tracheal branch. In 2 other patients, pathological FDG uptakes in cervical spine and mediastinum were not confirmed by other imaging techniques, and in the 2 remaining patients the scan results were inconclusive. The sensitivity of FDG-PET whole-body scan for detecting metastatic thyroid cancer was 60%.

CONCLUSIONS: This study indicates that the FDG-PET whole-body scan is a useful tool in the follow-up of patients with differentiated thyroid cancer, negative (131)I and (201)Tl scans and elevated serum thyroglobulin levels. The FDG-PET scan detects metastatic disease in 60% of patients with differentiated thyroid cancer, enabling surgical therapy to be performed on accessible lesions.