LAUSR

Objective To evaluate usefulness of [18F]fluorodeoxyglucose (FDG) PET/CT in patients with low detectable thyroglobulin levels suspicious for persistent or recurrent differentiated thyroid cancer (DTC). Methods A retrospective case series study evaluating FDG PET/CT in patients with detectable thyroglobulin (Tg) levels (≥ 0.20 ng/mL and <10.00 ng/mL) after initial treatment with total thyroidectomy and I-131 thyroid remnant ablation for pT1-3aN0-1bM0 DTC. Sensitivity, specificity, positive (PPV) and negative predictive value (NPV) of FDG PET/CT were calculated. Results Twenty-seven patients underwent FDG PET/CT. Median Tg level at FDG PET/CT was 2.00 ng/ml (range 0.30-9.00). FDG PET/CT was positive in 14 patients (51.9%): lesions suspicious for lymph node metastases were depicted in 12 patients, and lung metastases in 2. DTC was confirmed in 13/14 FDG PET/CT positive patients. In 9/13 patients with a negative FDG PET/CT DTC was confirmed ≤3 months after FDG PET/CT. The sensitivity, PPV, specificity and NPV were: 59.1%, 92.9%, 80.0% and 30.8%, respectively. Conclusions This case series shows that FDG PET/CT might be useful to detect persistent or recurrent DTC in patients with low detectable Tg. However, when FDG PET/CT is negative, this does not rule out DTC and further investigations are necessary.