Positron emission tomography-computed tomography with 18F-fluorodeoxyglucose in patients with recurrent differentiated thyroid carcinoma and negative radioiodine scan. Diagnostic performance and relation with thyroglobulin levels

Abstract Objective To assess the diagnostic performance of 18 F-FDG PET-CT scan and its relation to serum thyroglobulin (Tg) levels in patients with differentiated thyroid carcinoma with suspicion of persistence or recurrence of the disease and negative radioiodine scans. Material and methods This is a retrospective analysis of 35 PET-CT studies in 25 patients (17 women, average age 48.8 ± 15.2 years). The results were confirmed by histology or by ultrasonography and clinical follow-up. We analyzed the relationship between the diagnostic performance of the PET-CT scans and three levels of Tg: less than or equal to 2 ng/ml; between 2 and 10 ng/ml and greater than 10 ng/ml. Results We obtained 26 true-positives (TP), 1 false-positive (FP), 3 true-negatives (TN) and 5 false-negatives (FN). Of the 18 patients with PET-CTs classified as TP, 3 showed lesions at the post-thyroidectomy bed, 15 showed lymph node metastases and 5 had distant metastases. Sensitivity was 83.9% (CI 95%: 69.3–98.4%) and specificity was 75% (CI 95%: 20–100%). Regarding the three intervals of Tg, PET-CT scan showed true positive rates of 37.5%, 83% and 100% in patients with Tg levels of less than 2 ng/ml, between 2 and 10 ng/ml and more than 10 ng/ml, respectively. Conclusions 18 F-FDG PET-CT demonstrates high diagnostic yield in local disease and distant lesions for the population of patients with differentiated thyroid carcinoma and persistence of the disease with negative radioiodine scans at Tg levels above 2 ng/ml.