title: Fatigue as a cause, not a consequence of depression and daytime sleepiness: a cross-lagged analysis.
abstract: OBJECTIVE
  To examine the temporal relation between fatigue, depression, and daytime sleepiness after traumatic brain injury. Fatigue is a frequent and disabling consequence of traumatic brain injury (TBI). However, it is unclear whether fatigue is a primary consequence of the structural brain injury or a secondary consequence of injury-related sequelae such as depression and daytime sleepiness.
  
  
  METHODS
  Eighty-eight adults with complicated mild-severe TBI (69% male).
  
  
  METHODS
  Fatigue Severity Scale; depression subscale of the Hospital Anxiety and Depression Scale; Epworth Sleepiness scale at baseline and 6-month follow-up.
  
  
  RESULTS
  A cross-lagged path analysis computed within a structural equation modeling framework revealed that fatigue was predictive of depression (β = .20, P < .05) and sleepiness (β = .25, P < .05). However, depression and sleepiness did not predict fatigue (P > .05).
  
  
  CONCLUSIONS
  The results support the view of fatigue after TBI as "primary fatigue"-that is, a consequence of the structural brain injury rather than a secondary consequence of depression or daytime sleepiness. A rehabilitation approach that assists individuals with brain injury in learning to cope with their neuropsychological and physical limitations in everyday life might attenuate their experience with fatigue.
authors.affiliation: Department of Rehabilitation Psychology and Psychotherapy, Institute of Psychology, University of Freiburg, Germany (Dr Schönberger and Ms Herrberg); and School of Psychology and Psychiatry, Monash University (Drs Schönberger and Ponsford), Monash-Epworth Rehabilitation Research Centre, Epworth Hospital (Drs Schönberger and Ponsford), and National Trauma Research Institute (Dr Ponsford), Melbourne, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Schönberger
authors.forename: Marlene
authors.initials: M
authors.lastname: Herrberg
authors.forename: Jennie
authors.initials: J
authors.lastname: Ponsford
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001930:Brain Injuries / Q000150:complications* / Q000523:psychology; D003863:Depression / Q000150:complications* / Q000523:psychology; D005221:Fatigue / Q000209:etiology*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012720:Severity of Illness Index; D020178:Sleep Disorders, Circadian Rhythm / Q000150:complications*; D055815:Young Adult