The Diagnostic Value of 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Differentiated Thyroid Cancer Patients with Elevated Thyroglobulin/Thyroglobulin Antibody Levels and Negative Iodine Scintigraphy: A Systematic Review and Meta-Analysis

Background: The objective of this study is to evaluate the diagnostic accuracy of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in detecting recurrence in patients with differentiated thyroid cancer (DTC) who have negative whole-body scans (WBSs) but elevated serum thyroglobulin (Tg) or thyroglobulin antibody (TgAb) levels. Methods: This systematic review/meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis for Diagnostic Test Accuracy criteria (International Prospective Register of Systematic Reviews registration number: CRD42022340924). A comprehensive search of the MEDLINE, EMBASE, and Cochrane databases identified articles reporting the diagnostic accuracy of FDG PET/CT for the detection of recurrence in patients with DTC with negative WBS and elevated serum Tg or TgAb levels published between January 2012 and June 2023. Meta-analyses were performed to determine the diagnostic accuracy of FDG PET/CT on the total target population as well as on subgroups stratified by serum Tg or TgAb, and thyrotropin (TSH) stimulation status at the time of FDG PET/CT. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) framework was applied to evaluate the quality of evidence and the strength of recommendations to facilitate translation of the meta-analysis results into practical recommendations for clinical guidelines. Results: A total of 24 studies involving 1988 patients were included for analysis. The overall pooled sensitivity and specificity values were 0.87 (95% confidence interval [CI] = 0.83-0.92; I² = 75%) and 0.84 (CI = 0.80-0.89; I² = 44%), respectively. Subgroup analyses revealed no significant differences in the diagnostic accuracy of FDG PET/CT in patients stratified by serum Tg or TgAb levels, and TSH stimulation status at the time of PET/CT. Treatment plans were changed following FDG PET/CT imaging in 40% (CI = 34-47%; I² = 39%) of cases. The quality level of evidence for using FDG PET/CT was moderate in both sensitivity and specificity according to the GRADE system. Conclusion: There is moderate quality evidence demonstrating the high diagnostic accuracy of FDG PET/CT in detecting recurrence in patients with DTC with negative WBS and elevated serum Tg or TgAb levels. This evidence corroborates the current guidelines' endorsement of FDG PET/CT as a diagnostic tool in such patients.