TSH Stimulation before PET/CT as Our Frenemy in Detecting Thyroid Cancer Metastases-Final Results of a Retrospective Analysis.

Introduction: Non-iodine avid metastases of differentiated thyroid cancer (DTC) can be found using PET/CT with a fluorine-18-labeled glucose analog ([ ¹⁸ F]FDG). There are ongoing discussions on the appropriateness of using exogenous thyrotropin (TSH) stimulation before this examination. Material and Methods: In a retrospective study, 73 PET/CT scans with [ ¹⁸ F]FDG performed after exogenous stimulation with recombinant human TSH (rhTSH) and without such stimulation were analyzed. All analyzed patients were suspected of having non-iodine-avid foci of DTC. Results: The stimulation with rhTSH before the PET/CT did not affect the percentage of positive results: 37.5% (18/48) with rhTSH and 40% (10/25) without rhTSH ( p = 0.83). The analysis of the ROC curves established the cut-off thyroglobulin point for a positive PET/CT result separately for both subgroups. There was no statistically significant difference between obtaining a positive PET/CT result and the baseline thyroglobulin concentration (both stimulated and unstimulated). The exogenous stimulation of TSH prior to the PET/CT had no effect on the [ ¹⁸ F]FDG uptake in the PET/CT lesions. Conclusions: PET/CT with [ ¹⁸ F]FDG remains a useful method for the diagnosis of non-iodine-avid DTC lesions; in the presented group, a positive effect of rhTSH stimulation on the number of DTC foci visible in the PET/CT was found, but without affecting its effectiveness.