Are chronic fatigue and chronic fatigue syndrome valid clinical entities across countries and healthcare settings?

  • Prof Ian Hickie, Brain & Mind Research Institute, The University of Sydney, Australia
  • Tracey Davenport, Brain & Mind Research Institute, The University of Sydney, Australia
  • Dr Suzanne Vernon, Centers for Disease Control and Prevention, United States
  • Dr Rosane Nisenbaum, Centers for Disease Control and Prevention, United States
  • Dr William Reeves, Centers for Disease Control and Prevention, United States
  • Prof Andrew Lloyd, University of New South Wales, Australia

    • Objective: The validity of the diagnosis of chronic fatigue syndrome and related chronic fatigue states remains controversial, particularly in psychiatry. This project utilised international epidemiological and clinical research data to test construct validity across diagnostic categories, healthcare settings and countries.
    Methods: Relevant demographic, symptom and diagnostic data were obtained from 33 studies in 21 countries. The subjects had fatigue lasting one to six months (prolonged fatigue), or more than six months (chronic fatigue), or met diagnostic criteria for chronic fatigue syndrome. Common symptom domains were derived by factor analytic techniques. Mean scores on each symptom factor were compared across diagnostic categories, healthcare settings and countries.
    Results: Data were obtained on 37 724 subjects, including 42% from population-based studies, 52% from primary care studies, and 7% from secondary or specialist tertiary referral clinics. The sample also included 2 013 subjects with chronic fatigue, and 1 958 with chronic fatigue syndrome. A five-factor model of the key symptom domains was preferred (‘musculoskeletal pain/ fatigue’, ‘neurocognitive difficulties’, ‘inflammation’, ‘sleep disturbance/ fatigue’ and ‘mood disturbance’) and was comparable across subject groups and settings. While the core symptom profiles were similar, some differences in symptoms were observed across diagnostic categories, healthcare settings and between countries.
    Conclusions: The construct validity of chronic fatigue and chronic fatigue syndrome is supported by an empirically-derived factor structure from existing international datasets.