title: Inflammation of unknown origin versus fever of unknown origin: two of a kind.
abstract: OBJECTIVE
  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. (18)F-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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Internal Medicine, Unit of General Internal Medicine, University Hospital Leuven, Leuven, Belgium. Steven.Vanderschueren@uz.kuleuven.ac.be
authors.forename: Steven
authors.initials: S
authors.lastname: Vanderschueren
authors.forename: Elke
authors.initials: E
authors.lastname: Del Biondo
authors.forename: David
authors.initials: D
authors.lastname: Ruttens
authors.forename: Inge
authors.initials: I
authors.lastname: Van Boxelaer
authors.forename: Els
authors.initials: E
authors.lastname: Wauters
authors.forename: Daniël D C
authors.initials: DD
authors.lastname: Knockaert
mesh_terms: D000328:Adult; D000368:Aged; D002097:C-Reactive Protein / Q000378:metabolism; D016208:Databases, Factual; D003953:Diagnosis-Related Groups / Q000145:classification*; D005260:Female; D005335:Fever of Unknown Origin / Q000000981:diagnostic imaging* / Q000209:etiology / Q000401:mortality; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D006801:Humans; D007239:Infections / Q000150:complications / Q000000981:diagnostic imaging*; D007249:Inflammation / Q000000981:diagnostic imaging* / Q000209:etiology / Q000401:mortality; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000150:complications / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography; D012216:Rheumatic Diseases / Q000150:complications / Q000000981:diagnostic imaging
chemical_list: D019788:Fluorodeoxyglucose F18; D002097:C-Reactive Protein