Role of FDG-PET/CT in the Diagnosis of Fever or Inflammation of Unknown Origin (FUO/IUO)

Fever of unknown origin (FUO) is a syndrome of fever without obvious cause, and it is regarded as a difficult diagnostic challenge. Inflammation of unknown origin (IUO) is similar to FUO, except that it is not associated with elevated body temperature. FDG-PET/CT may cover the diagnosis of a wide spectrum of diseases causing FUO/IUO, namely tumors and inflammation, under the conditions that the disease is active (consuming a lot of glucose), and the lesion is focal and of a size that is sufficiently larger than the limit of detectability. Promising results of FDGPET/CT for the diagnosis of FUO/IUO have been reported from many institutions. FDGPET/CT is very helpful for recognizing and excluding diseases, directing further diagnostic decisions, and avoiding unnecessary invasive examinations. If confirmed by further studies, FDG-PET/CT may become established as an initial, noninvasive diagnostic tool in the evaluation of FUO/IUO.