Endocrine Abstracts

Aim: To address the role of FDG/PET-CT in the follow-up of DTC.

Methods: About 110 consecutive patients (86 female, 24 male, mean age 45±13 years), with DTC were selected between 1999 and 2006. All patients underwent total thyroidectomy, radioiodine ablation and had undetectable serum thyroglobulin (Tg) during L-T₄ suppressive therapy and negative serum TgAb. The follow-up included a yearly clinical examination with neck ultrasonography (US) and Tg determination after rhTSH stimulation. All subjects with elevated Tg and negative US underwent FDG/PET-CT.

Results: Tg levels were undetectable during TSH-suppressive therapy in all patients. After rhTSH, Tg values remained undetectable in 81 patients, whereas 29/110 became detectable during follow-up.

At 12–24months, 8/29 cases showed low detectable Tg values (<2 ng/ml).US detected suspicious cervical lymph node metastases in three cases confirmed by FNAC, while Tg values became undetectable during subsequent surveillance in the other 5 cases.

At 24–36 months, 7/29 patients showed serum Tg >2<5 ng/ml and underwent US and FDG/PET-CT. Suspicious cervical lymph node metastases were detected in 2 patients by US and 1 by FDG-PET, confirmed by FNAC, and 4 patients with negative US and PET went through a Tg stimulation test after TSH withdrawal 6–12 months later. Four patients showed a persistent Tg increase but only one tested positive in the lung by PET/TC.

At 36–60 months, 14/29 cases had serum Tg levels >5 ng/ml: 4 showed uptake in the mediastinal region, 4 in the cervical region, 1 case in the lung and 1 both in the cervical and mediastinal regions by FDG/PET-TC. The remaining 4 patients tested negative through additional imaging (CT, MRI).

Conclusion: During the first years of follow-up, US was highly sensitive in detecting recurrence of cervical disease. FDG-PET-CT scan is a useful diagnostic test to detect and localize metastases when post-rhTSH Tg is >5 ng/ml in the later period of follow-up.