Value of the negative PET-FDG in the middle term follow-up of differentiated thyroid cancer in patients with negative 131I-Na scan and elevated thyroglobulin serum levels

Abstract

ObjectiveThis study has aimed to analyze the evolution of patients diagnosed with differentiated thyroid carcinoma (DTC) with a negative 131I-Na whole body scan (WBS), high levels of serum thyroglobulin (Tg) and negative 18F-fluorodeoxyglucose positron emission tomography (PET-FDG) study. Material and methodsTwenty-three patients diagnosed and treated for DTC were studied retrospectively. Patients were aged between 23 and 83 and had shown, between January 2001 and December 2002, negative WBS, Tg values in a range of suspected recurrence or metastasis (Tg>2ng/mL with thyroid hormone withdrawal) and a negative PET-FDG study. The patients were monitored clinically, radiologically and analytically for a minimum period of 4 years. After this, a new evaluation was made of their state of disease with a control WBS, also observing the evolution of Tg. All WBS were performed with a 185MBq diagnostic dose of 131I-Na. ResultsIn 18/23 patients, Tg decreased and in 5 it increased. Four patients (17%) were free of active disease (negative WBS Tg<2ng/mL). A total of 16 patients (70%) were free of disease according to the WBS but had elevated Tg. Three patients (13%) had disease and high levels of Tg, two of them with positive WBS and the third with positive 99mTc-MIBI scan and CT. ConclusionsMost patients with a negative WBS, high Tg serum levels and negative PET-FDG had good evolution, with descending Tg levels, normal levels even being reached in a significant percentage of them.