Diagnostic performance of 18 F‐FDG‐PET/CT in inflammation of unknown origin: A clinical series of 317 patients

International audience; Background: Inflammation of unknown origin (IUO) is a challenging situation in internal medicine.Objectives: To describe the final diagnoses in IUO and assess the helpfulness of 18F-fluorodesoxyglucose positron emission tomography with computerized tomography (18F-FDG-PET/CT) in the diagnosis strategy.Results: A total of 317 IUO patients with 18F-FDG-PET/CT were enrolled. A diagnosis was reached in 228 patients: noninfectious inflammatory diseases (NIID) (37.5%), infectious diseases (18.6%), malignancies (7.9%), and non-systemic-inflammatory miscellaneous diseases (7.9%). The two leading causes of NIID were polymyalgia rheumatica and giant cell arteritis. 18F-FDG-PET/CT results were classified as true positive in 49.8% of patients and contributory in 75.1% of overall IUO patients (after the complete investigation set and a prolonged follow-up). In multivariate analysis, only C-reactive protein minimum level (≥50 mg/L) was associated with the contributory status of 18F-FDG-PET/CT.Conclusion: Within the wide spectrum of IUO underlying diseases, 18F-FDG-PET/CT is helpful to make a diagnosis and to eliminate inflammatory diseases. Obese patients constitute a specific group needing further studies