18F-FDG-PET/CT imaging in fever and inflammation of unknown origin

Abstract

18F-FDG-PET/CT has gained an important place in the diagnostic work-up of patients with fever of unknown origin (FUO) and inflammation of unknown origin (IUO), which are defined as elevated body temperature or elevated inflammatory parameters for several weeks without an explanation, despite intensive investigation in an immunocompetent patient. Relying on the uptake of 18F-FDG-FDG in inflammatory cells, 18F-FDG-PET/CT may detect both infection and non-infectious inflammation, as well as malignancy, which all can cause FUO/IUO. Fever, CRP, and ESR can be used as parameters for the timing of 18F-FDG-PET/CT. When all of these are absent within the days before 18F-FDG-PET/CT, there is a high chance of non-contributory 18F-FDG-PET/CT. When performed at the right moment, 18F-FDG-PET/CT contributes to the final diagnosis in 48–62% of patients in meta-analyses. 18F-FDG-PET/CT could be cost-effective, as it may save up to 7000 Euros per patient when used at an early stage. When no abnormal 18F-FDG uptake is observed on PET/CT in a patient remaining without a final diagnosis, this may predict a higher chance of spontaneous resolution. When 18F-FDG-PET/CT is unavailable, gallium scintigraphy, or full body MR may be used as an alternative, but all of these are inferior to 18F-FDG-PET/CT. Labeled leukocyte scintigraphy can be useful as an alternative to 18F-FDG-PET/CT, particularly in patients with a high pre-test probability of infection. In the future, new tracers, and the combination of PET with MRI may increase the diagnostic value of PET in FUO/IUO.