Fever of Unknown Origin

Molecular imaging methods can help in the diagnosis in patients with fever of unknown origin (FUO) based on its earlier functional rather than morphological and structural changes. An infection or inflammatory process underlies 40 % of the cases of FUO. Malignancies, autoimmune noninfectious diseases, and miscellaneous are the origin of the remainder. PET alone is superior to CT in identifying inflammatory process in patients with FUO, considering that inflammation causes overexpression of the GLUT-1 and GLUT-2 transporters in leukocytes, which will accordingly take up large amounts of labeled FDG. Multislice CT technology usually contributes to the final diagnosis of FUO in 40 % of the cases. The combination of 18F-FDG–PET and CT allows both molecular and morphological imaging, which makes this combined imaging modality a potentially useful tool in the evaluation of FUO. Moreover, PET can reveal otherwise occult malignancies as well as paraneoplastic syndromes related to malignant diseases, both of which may initially manifest as FUO.