Fluorodesoxyglucose Positron Emission Tomography (PET/CT) has never been compared to Chest-Abdomen-Pelvis CT (CAPCT) in patients with a fever of unknown origin (FUO), inflammation of unknown origin (IUO) and episodic fever of unknown origin (EFUO) through a prospective and multicentre study. In this study, we investigated the diagnostic value of PET/CT compared to CAPCT in these patients. The trial was performed between 1 May 2008 through 28 February 2013 with 7 French University Hospital centres. Patients who fulfilled the FUO, IUO or EFUO criteria were included. Diagnostic orientation (DO), diagnostic contribution (DC) and time for diagnosis of both imaging resources were evaluated. One hundred and three patients were included with 35 FUO, 35 IUO and 33 EFUO patients. PET/CT showed both a higher DO (28.2% vs. 7.8%, p < 0.001) and DC (19.4% vs. 5.8%, p < 0.001) than CAPCT and reduced the time for diagnosis in patients (3.8 vs. 17.6 months, p = 0.02). Arthralgia (OR 4.90, p = 0.0012), DO of PET/CT (OR 4.09, p = 0.016), CRP > 30 mg/L (OR 3.70, p = 0.033), and chills (OR 3.06, p = 0.0248) were associated with the achievement of a diagnosis (Se: 89.1%, Sp: 56.8%). PET/CT both orients and contributes to diagnoses at a higher rate than CAPCT, especially in patients with FUO and IUO, and reduces the time for diagnosis.

While the diagnosis of adult-onset Still’s disease (AOSD) involves the exclusion of differential diagnoses, the characteristics and value of 18F-Fluorodeoxyglucose (18F-FDG) Positron Emission Tomography coupled with CT (PET/CT) in the management of AOSD remain poorly known. Our retrospective study included patients from four centers, fulfilling Yamaguchi or Fautrel criteria, who underwent a PET/CT during an active AOSD. Thirty-five patients were included. At the time of PET/CT, the Yamaguchi criteria were met in 23 of 29 evaluable cases. PET/CT showed bone marrow (74.3%), lymph node (74.3%), and splenic (48.6%) FDG uptake. Despite arthralgia or arthritis in most patients, joints were rarely the sites of 18F-FDG accumulation. The spatial distribution of 18F-FDG uptake was nonspecific, and its intensity could be similar to malignant disease. Lymph node or bone marrow biopsy was performed after PET/CT in 20 patients (57.1%). The intensity of bone marrow; splenic and lymph node hypermetabolism appeared to be correlated with disease activity. Abnormal PET/CT in the cervical lymph nodes and age ≥ 60 years seemed to be predictive factors for monocyclic evolution. The clinical value of PET/CT is not in direct diagnosis; but as an aid in excluding differential diagnoses by searching for their scintigraphic features and guiding biopsy.