title: Chronic fatigue syndrome--a clinically empirical approach to its definition and study.
abstract: BACKGROUND
  The lack of standardized criteria for defining chronic fatigue syndrome (CFS) has constrained research. The objective of this study was to apply the 1994 CFS criteria by standardized reproducible criteria.
  
  
  METHODS
  This population-based case control study enrolled 227 adults identified from the population of Wichita with: (1) CFS (n = 58); (2) non-fatigued controls matched to CFS on sex, race, age and body mass index (n = 55); (3) persons with medically unexplained fatigue not CFS, which we term ISF (n = 59); (4) CFS accompanied by melancholic depression (n = 27); and (5) ISF plus melancholic depression (n = 28). Participants were admitted to a hospital for two days and underwent medical history and physical examination, the Diagnostic Interview Schedule, and laboratory testing to identify medical and psychiatric conditions exclusionary for CFS. Illness classification at the time of the clinical study utilized two algorithms: (1) the same criteria as in the surveillance study; (2) a standardized clinically empirical algorithm based on quantitative assessment of the major domains of CFS (impairment, fatigue, and accompanying symptoms).
  
  
  RESULTS
  One hundred and sixty-four participants had no exclusionary conditions at the time of this study. Clinically empirical classification identified 43 subjects as CFS, 57 as ISF, and 64 as not ill. There was minimal association between the empirical classification and classification by the surveillance criteria. Subjects empirically classified as CFS had significantly worse impairment (evaluated by the SF-36), more severe fatigue (documented by the multidimensional fatigue inventory), more frequent and severe accompanying symptoms than those with ISF, who in turn had significantly worse scores than the not ill; this was not true for classification by the surveillance algorithm.
  
  
  CONCLUSIONS
  The empirical definition includes all aspects of CFS specified in the 1994 case definition and identifies persons with CFS in a precise manner that can be readily reproduced by both investigators and clinicians.
authors.affiliation: Division of Viral and Rickettsial Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA. wcr1@cdc.gov
authors.forename: William C
authors.initials: WC
authors.lastname: Reeves
authors.forename: Dieter
authors.initials: D
authors.lastname: Wagner
authors.forename: Rosane
authors.initials: R
authors.lastname: Nisenbaum
authors.forename: James F
authors.initials: JF
authors.lastname: Jones
authors.forename: Brian
authors.initials: B
authors.lastname: Gurbaxani
authors.forename: Laura
authors.initials: L
authors.lastname: Solomon
authors.forename: Dimitris A
authors.initials: DA
authors.lastname: Papanicolaou
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Unger
authors.forename: Suzanne D
authors.initials: SD
authors.lastname: Vernon
authors.forename: Christine
authors.initials: C
authors.lastname: Heim
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D015992:Body Mass Index; D016022:Case-Control Studies; D003863:Depression / Q000175:diagnosis; D019937:Diagnostic Techniques and Procedures / Q000592:standards*; D015673:Fatigue Syndrome, Chronic / Q000145:classification / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D011446:Prospective Studies; D012720:Severity of Illness Index