The Additive Clinical Value of 18F-FDG PET/CT in Defining the Recurrence of Disease in Patients With Differentiated Thyroid Cancer Who Have Isolated Increased Antithyroglobulin Antibody Levels

AIMThe aim of this study was to investigate the additive clinical value of F-FDG PET/CT in defining the recurrence of disease in patients with differentiated thyroid cancer (DTC) who have isolated increased antithyroglobulin antibody (TgAb) levels with undetectable thyroglobulin (Tg) levels and negative I whole-body scintigraphy (wbs). MATERIALS AND METHODSClinical follow-up data of 231 patients with DTC who underwent F-FDG PET/CT between June 2006 and March 2011 were evaluated retrospectively. There were a total of 48 patients who underwent F-FDG PET/CT for isolated increased serum TgAb levels. When 17 patients who have lymphocytic thyroiditis were excluded, the remaining 31 patients [27 women and 4 men; mean (SD) age, 50.29 (15.2) y] were included in this study. The inclusion criteria were undetectable serum Tg and increased TgAb levels under the condition of thyroid-stimulating hormone greater than 30 IU/mL with negative I wbs and absence of pathologic findings in neck ultrasound and thoracic CT if performed. Findings from the F-FDG PET/CT were compared with the clinical follow-up data and the results of histopathologic examinations. RESULTSResults of F-FDG PET/CT were negative in 15 and positive in 16 patients. Sixteen FDG-positive sites (15 lymph nodes and 1 bone) were seen in 16 patients who had positive findings in F-FDG PET/CT. In the comparison with F-FDG PET/CT findings and clinical follow-up data and histopathologic examination results, 4, 12, 2, and 13 patients were false-positive, true-positive, false-negative and true-negative retrospectively. In the receiver operating characteristic analysis, a 5.4 cutoff SUVmax value was calculated with 82% sensitivity and 81% specificity in distinguishing malignant and benign lesions. As a result, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of F-FDG PET/CT in the detection of recurrent disease were calculated as 75%, 76%, 75%, 86%, and 80%, respectively. CONCLUSIONSIsolated increased TgAb levels might be a predictor of the recurrent DTC and F-FDG PET/CT might be an additive imaging method in detecting the recurrent disease in patients with DTC who have increased TgAb levels with undetectable Tg levels and negative I wbs.