title: Latent class analysis of symptoms associated with chronic fatigue syndrome and fibromyalgia.
abstract: BACKGROUND
  Chronic fatigue syndrome and fibromyalgia continue to be perplexing conditions of unknown validity. Aetiological and symptomatic heterogeneity is likely and the distinctiveness of these disorders remains unclear. Our aims were to investigate empirically symptomatic heterogeneity in chronic fatigue syndrome and fibromyalgia.
  
  
  METHODS
  Latent class analysis was applied to data from 646 patients who met accepted criteria for chronic fatigue syndrome and/or fibromyalgia who were systematically evaluated at a specialist fatigue clinic. Thirty-two symptoms commonly found in chronic fatigue syndrome and fibromyalgia were entered into the latent class analysis.
  
  
  RESULTS
  We chose to interpret a four class solution. The classes appeared to differ in a graded fashion (rather than qualitatively) for symptom endorsements, pre-morbid characteristics, and co-morbidity with panic disorder and major depression.
  
  
  CONCLUSIONS
  These results were unexpected given the usual assumption of the distinctiveness of chronic fatigue syndrome and fibromyalgia. These results support a conceptualization of chronic fatigue syndrome and fibromyalgia as being characterized by greater similarities than differences.
authors.affiliation: Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond 23298-0126, USA.
authors.forename: P F
authors.initials: PF
authors.lastname: Sullivan
authors.forename: W
authors.initials: W
authors.lastname: Smith
authors.forename: D
authors.initials: D
authors.lastname: Buchwald
mesh_terms: D000328:Adult; D015897:Comorbidity; D003865:Major Depressive Disorder / Q000145:classification / Q000175:diagnosis / Q000523:psychology; D003937:Diagnosis, Differential; D015673:Fatigue Syndrome, Chronic / Q000145:classification / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D005356:Fibromyalgia / Q000145:classification / Q000175:diagnosis* / Q000523:psychology; D006801:Humans; D008297:Male; D008432:Mathematical Computing; D008875:Middle Aged; D015233:Models, Statistical; D016584:Panic Disorder / Q000145:classification / Q000175:diagnosis / Q000523:psychology; D010348:Patient Care Team; D012803:Sick Role