ABSTRACT

Fever of unknown origin (FUO) is defined as a pattern of fever that does not resolve spontaneously and in which etiology remains unknown after initial diagnostic evaluation. FUO was originally defined in 1961 by Petersdorf and Beeson as an illness with recurrent fever of more than 38.3 °C (101 ⁰F), lasting 3 weeks or more without a reason and remaining undiagnosed after 1 week of detailed clinical investigation in hospital. In 1992, Durak and Street have modified this definition by excluding nosocomial infections and immunocompromised patients and adding the criteria of outpatient visits. It was reported that the spectrum of FUO etiology may include more than 200 diseases. Differential diagnosis of FUO includes a wide spectrum of diseases as infections, autoimmune conditions and malignancies. The diagnostic workup of FUO needs a detailed clinical, laboratory and radiological investigations. F-18 fluoro-D-glucose (FDG) positron emission tomography/computed tomography (F-18 FDG PET/CT) is an established hybrid imaging technique especially in the field of oncology but recently it has been shown to be a useful modality in the evaluation of infectious and inflammatuary conditions. It is an important advantage of F-18 FDG PET/CT to provide morphological information in addition to anatomical information. Although F-18 FDG PET/CT has limited value in differentiation of malignancy/infection-inflammation; positive findings detected in F-18 FDG PET/CT can be used to guide additional diagnostic tests that lead to the final diagnosis. F-18 FDG PET/CT has a great advantage in malignant pathologies, infectious and inflammated diseases as it can detect a wider spectrum of diseases much earlier compared with Ga-67 citrate scintigraphy and labeled leukocyte scintigraphy. Another advantage of this technique is its high negative predictive value. Negative F-18 FDG PET/CT findings help to rule out morphologically detectable focus of fever and potentially serious and dangerous pathologies such as lymphoma or vasculitis. In the literature there are many publications indicating the diagnostic performance and also superiority to other radiological/radionuclide imaging techniques of F-18 FDG PET/CT in the management of FUO. Although F-18 FDG-PET/CT is an expensive technique and its availability is still limited in some countries as compared with CT and scintigraphy techniques, F-18 FDG-PET/CT can be cost effective in the FUO diagnostic workup if it is used at an early stage, leading to an early diagnosis. By this way hospitalization period as well as number of routine diagnostic procedures and repetition of unnecessary and unhelpfull tests are reduced. As a result, prospective, structred multicentered studies involving F-18 FDG-PET/CT as first line tool in diagnosis in early stages of disease are required to investigate and improve the diagnostic performance of F-18 FDG-PET/CT in FUO management.