Impact of TSH stimulation on 2-[18F]FDG PET/CT results in patients with papillary thyroid carcinoma presented with elevated serum thyroglobulin level and negative diagnostic iodine-131 whole-body scan

2-[18F]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (2-[18F]FDG-PET/CT) is implemented in papillary thyroid cancer (PTC) patients with elevated Thyroglobulin (Tg) and negative Iodine-131 whole-body scan (131I-WBS). Here, we evaluated the impact of TSH stimulation after levothyroxine withdrawal on the detection rate of 2-[18F]FDG-PET/CT. A prospective study was performed on 60 PTC patients, presented with negative 131I-WBS and elevated or unjustifiably high Tg. 2-[18F]FDG-PET/CT was performed in 30 patients while they were on levothyroxine therapy (unstimulated-TSH [uns-TSH]) and after Levothyroxine withdrawal in the other 30 patients (stimulated-TSH [s-TSH]). Results of the two groups were compared using nonparametric tests. Receiver operating characteristic curve was used to find Tg cutoff values for predicting positive scan results. Overall, 2-[18F]FDG-PET/CT was positive in 63.3% of the patients, 80% (24/30) in s-TSH and 46.7% (14/30) in uns-TSH group. The detection rate was higher in s-TSH group (p=0.007). It was still significant in multiple regression analysis (p=0.041). In uns-TSH group, 2-[18F]FDG-PET/CT was more often positive in patients with higher uns-Tg level (p=0.002). An uns-Tg level of ≥19.00 ng/mL predicted positive results with the sensitivity of 0.786 and specificity of 0.750 (area under curve=0.819). Although statistically insignificant (p=0.055), s-Tg was higher in patients with positive 2-[18F]FDG-PET/CT studies in the s-TSH group. No relation was demonstrated between TSH and anti-Tg-antibody levels and 2-[18F]FDG-PET/CT positivity. TSH-stimulation after levothyroxine withdrawal might enhance the detection rate of 2-[18F]FDG-PET/CT in PTC patients. Additionally, 2-[18F]FDG-PET/CT is more often positive in patients with higher Tg levels.