title: Analysis of 256 cases of classic fever of unknown origin.
abstract: OBJECTIVE
  The causes of fever of unknown origin (FUO) vary depending on the region and time period. We herein present a study of patients with classic FUO where we investigated differences based on patient background factors, such as age and causative diseases, and changes that have occurred over time.
  
  
  METHODS
  We extracted and analyzed data from the medical records of 256 patients ≥18 years old who met the criteria for classic FUO and were hospitalized between August, 1994 and December, 2012.
  
  
  RESULTS
  The median age of the patients was 55 years (range: 18-94 years). The cause of FUO was infection in 27.7% of the patients (n=71), non-infectious inflammatory disease (NIID) in 18.4% (47), malignancy in 10.2% (26), other in 14.8% (38), and unknown in 28.9% (74). The most common single cause was human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) (n=17). NIID and malignancy were more common in patients ≥65 years old than in patients <65 years old. During 2004-2012, compared to 1994-2003, infections and "other" causes were decreased, whereas NIID, malignancy, and unknown causes were increased.
  
  
  CONCLUSIONS
  FUO associated with HIV/AIDS is increasing in Japan. In addition, as in previous studies in Japan and overseas, our study showed that the number of patients in whom the cause of FUO remains unknown is increasing and exceeds 20% of all cases. The present study identified diseases that should be considered in the differential diagnosis of FUO, providing useful information for the future diagnosis and treatment of FUO.
authors.affiliation: Department of General Medicine, Juntendo University School of Medicine, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Yamanouchi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Uehara
authors.forename: Hirohide
authors.initials: H
authors.lastname: Yokokawa
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Hosoda
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Shiga
authors.forename: Akihiro
authors.initials: A
authors.lastname: Inui
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Otsuki
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Fujibayashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Isonuma
authors.forename: Toshio
authors.initials: T
authors.lastname: Naito
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005335:Fever of Unknown Origin / Q000209:etiology* / Q000473:pathology; D015658:HIV Infections / Q000150:complications; D006801:Humans; D007249:Inflammation / Q000150:complications; D007564:Japan; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000150:complications; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D055815:Young Adult