The role of 18F-FDG PET/CT in the follow-up of well-differentiated thyroid cancer with negative thyroglobulin but positive and/or elevated antithyroglobulin antibody.

Thyroglobulin measurement is the most sensitive and important indicator of persistent and/or recurrent disease in the follow-up of well-differentiated thyroid cancer (DTC) after total thyroidectomy and radioiodine ablation therapy. However, positive or elevated thyroglobulin autoantibody (TgAb) interferes with the accurate measurement of serum thyroglobulin and may mask the presence of a recurrent and/or metastatic disease. It was reported that persistently positive TgAb could be viewed as evidence of the continued presence of functional thyroid cells, either benign or malignant, and elevated TgAb might indicate the recurrent and/or metastatic disease and could be used as an alternative of the tumor marker for DTC. However, the clinical application and usefulness of TgAb for the follow-up of DTC are uncertain. Imaging studies such as the neck ultrasound and whole-body radioiodine are still used widely for the detection of the lesions. Although it is not used routinely in DTC, limited clinical observations showed that fluorine-18-fluorodeoxyglucose (F-FDG) PET/computed tomography could be an additive valuable imaging modality in the detection of recurrent and/or metastatic disease in these patients, with promising sensitivity and specificity. A negative F-FDG PET/computed tomography result was associated with the absence of active disease and disappearing TgAb over time, and F-FDG-avid residual/recurrent/metastatic lesions were associated with aggressive disease, poor outcome, and persistently increased TgAb levels.