Methods: The utility of Fluorine-18 fluorodeoxyglucose positron emission tomography/CT in identifying the causal source was assessed in this retrospective study. A total of 68 patients (33 men, 35 women; age range, 23-91 years) with fever of unknown origin (FUO) underwent a positron emission tomography/computed tomography (PET/CT) scan. PET/CT was considered helpful when abnormal results allowed an accurate diagnosis, based on histopathology, microbiologic assays, or clinical and imaging follow-up.
Results: PET/CT demonstrated suspected pathologic foci of Fluorine-18 fluorodeoxyglucose (F-18 FDG) uptake in 41 patients (60%), in 38 of these 41 patients (93%) F-18 FDG PET/CT helped in identifying the causal source, including infection in 25 patients, inflammation in 11 patients, a benign neoplasm in 1 patient, and in 1 patient rejection of a pancreas transplant. In 27 negative F-18 FDG PET/CT studies, no focal pathologic disease was diagnosed in the follow-up. In 6 of these 27 patients, a systemic disease without a focal manifestation was the cause for FUO. In the remaining 21 patients, fever and other signs subsided during follow-up.
Conclusion: Overall 56% of the F-18 FDG PET/CT studies contributed in the identification of the source in patients with FUO, and elevated erythrocyte sedimentation rate and C-reactive protein (positive predictive value 93%). When systemic diseases are excluded F18-FDG PET/CT has a high negative predictive value for focal etiologies of FUO (negative predictive value 100%).