Importance of positron emission tomography and computed tomography (PET CT) in fever of unknown origin (FUO) and inflammation of unknown origin (IUO)

Background: Fever of unknown origin (FUO) and inflammation of uknown origin (IUO) are common problems and diagnostic process is difficult for clinicians. Patients are exposed to extensive and expensive medical examinations for the identification of the FUO/IUO. FDG PET/CT can help to identify the underlying disease in these patients [1,2]. Objective: The aim of this study was to evaluate the role of PET/CT in patients with FUO/IUO and to identfy FDG uptake sites and patterns. Methods: Total of 286 patients who were performed 18F FDG-PET/CT between January 2014 and December 2017 were evaluated retrospectively. 62 patients who had PET/CT scan for FUO/IUO were examined for definitive diagnosis, PET/CT patterns, organ involvement and SUVmax values. Results: Out of total 62 patients who received PET / CT for FUO/IUO; rheumatic disease in 27 patients (43.5%), malignancy in 20 patients (32.3%) and infectious diseases in 6 patients (9.7%) was found. Clinically significant FDG uptake in 36 patients (61.6%) is found in PET / CT reports of 60 patients with FUO/IUO. 17 of the 20 patients (85%) with malignancy were found to be positive for diagnosis in PET. 19 of the 25 patients (76%) diagnosed with rheumatologic disease FDG uptake was determined. A total of 62 patients who received PET / CT for FUO/IUO 11 (17.7%) were diagnosed with vasculitis. In our study, a total of 9 patients were diagnosed with Takayasu arteritis. Significant vascular FDG involvement was detected (77.7%). Other imaging modalities before PET / CT shows no pathological finding for Takayasu arteritis in 4 of 7 patients. Among the groups diagnosed as malignancy and rheumatologic disease due to FUO/IUO FDG uptake in the PET / CT, lymph node (p = 0.013) and bone (p = 0.005) malignancy group was significantly higher. Vascular involvement (p = 0.001) was significantly higher in the group diagnosed with rheumatic disease. The highest FDG uptake in PET / CT SUVmax mean value was significantly higher in the malignancy group (p = 0.001). Conclusion: Our findings revealed that PET/CT is a useful imaging modality in the FUO/IUO patients who have very difficult diagnostic process for clinicians. In these patients, inflammatory diseases should be considered in addition to malignancies and PET / CT was found to be superior to other imaging modalities in the detection of vascular inflammations.