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

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.

MATERIALS 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: ≤2ng/ml; between 2 and 10 ng/ml, and >10ng/ml.

RESULTS: We obtained 26 true-positives (TP), one 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 were distant metastases. Sensitivity was 83.9% (95%CI: 69.3%-98.4%) and specificity was 75% (95%CI: 20%-100%). Regarding the three intervals of Tg, PET-CT scan showed TP rates of 37.5%, 83% and 100% in patients with Tg levels <2ng/ml, between 2 and 10ng/ml, and >10ng/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 2ng/ml.