Aim: The aim of this study was to investigate the additive clinical value of 18F-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 131I whole-body scintigraphy (wbs).
Materials and methods: Clinical follow-up data of 231 patients with DTC who underwent 18F-FDG PET/CT between June 2006 and March 2011 were evaluated retrospectively. There were a total of 48 patients who underwent 18F-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 131I wbs and absence of pathologic findings in neck ultrasound and thoracic CT if performed. Findings from the 18F-FDG PET/CT were compared with the clinical follow-up data and the results of histopathologic examinations.
Results: Results of 18F-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 18F-FDG PET/CT. In the comparison with 18F-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 18F-FDG PET/CT in the detection of recurrent disease were calculated as 75%, 76%, 75%, 86%, and 80%, respectively.
Conclusions: Isolated increased TgAb levels might be a predictor of the recurrent DTC and 18F-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 131I wbs.