Inflammation of unknown origin versus fever of unknown origin: Two of a kind

Objectives: A vast literature exists on fever of unknown origin (FUO), characterized by prolonged and perplexing fevers >38.3 degrees C. In contrast, no studies are available to guide the approach to inflammation of unknown origin (IUO), defined as prolonged and perplexing inflammation with temperatures <38.3 degrees C. We aimed to determine the diagnostic yield, the case-mix, and the outcome of patients with IUO, relative to patients with FUO. Methods: We matched 57 patients with IUO to 57 patients with FUO of the same gender (54% male) and a similar age (median: 67 years). Results: A diagnosis was established in 35 patients with IUO (61%) and in 33 patients with FUO (58%) (p=.70). The case-mix did not differ significantly (p=.43). Non-infectious inflammatory disorders were the dominant diagnostic category in the IUO group (16 patients), while in the FUO group, similar numbers of malignancies [10], infections [9], and non-infectious inflammatory diseases [9] were diagnosed. F-18-fluorodeoxyglucose-positron emission tomography (FDG-PET) scan contributed comparably to the diagnosis in both groups (in 18 of 50, 36%, patients with IUO and in 13 of 40.33%, patients with FUO) (p=.83). In both groups, 7 patients (12%) died during an average follow-up of 1 year. Conclusion: Diagnostic yield, case-mix, contribution of FDG-PET scan and vital outcome were similar in patients with IUO and FUO. These data suggest that the 38.3 degrees C boundary may be arbitrary and that the diagnostic approaches used in FUO can be applied to IUO. (C) 2009 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.