Optimal use of [18F]FDG-PET/CT in patients with fever or inflammation of unknown origin

[18F]FDG-PET/CT is one of the most important diagnostic techniques in the work-up of patients with fever of unknown origin (FUO)/inflammation of unknown origin (IUO). Little is known on how to optimize the diagnostic value of [18F]FDG-PET/CT in patients with FUO/IUO.Retrospective study in all patients who underwent [18F]FDG-PET/CT during the work-up of FUO/IUO in a tertiary expert center between 2005 and 2014. Data were extracted from medical records.One hundred and four patients were identified, of whom 68 had a final diagnosis (65.4%). Mainly infections (30.8%) and non-infectious inflammatory diseases (30.8%). [18F]FDG-PET/CT contributed to the final diagnosis in 47 of the 68 patients (69.1%). In 21 patients [18F]FDG-PET/CT did not help making a diagnosis. In ten of these patients [18F]FDG-PET/CT was performed while body temperature, CRP and ESR were normal or unknown. Sixteen of 104 patients underwent repeated [18F]FDG-PET/CT. The second scan contributed to the final diagnosis in five of these patients. In two of these patients, the first scan retrospectively was truly non-contributory. In both patients the first [18F]FDG-PET/CT was made while CRP/ESR was low and fever was not present or not measured. A third or fourth scan never contributed to the final diagnosis when the second one did not.[18F]FDG-PET/CT contributed to the final diagnosis in 45.2% of patients, but never contributed when both inflammatory parameters and body temperature were normal. Repeating [18F]FDG-PET/CT should only be done in patients with a non-contributory [18F]FDG-PET/CT when new symptoms or signs appear, or when the first scan was made in absence of fever or elevated inflammatory parameters.