title: Rehabilitative therapies for chronic fatigue syndrome: a secondary mediation analysis of the PACE trial.
abstract: BACKGROUND
  Cognitive behaviour therapy (CBT) added to specialist medical care (SMC), or graded exercise therapy (GET) added to SMC, are more effective in reducing fatigue and improving physical function than both adaptive pacing therapy (APT) plus SMC and SMC alone for chronic fatigue syndrome. We investigate putative treatment mechanisms.
  
  
  METHODS
  We did a planned secondary mediation analysis of the PACE trial comparing SMC alone or SMC plus APT with SMC plus CBT and SMC plus GET for patients with chronic fatigue syndrome. 641 participants were recruited from six specialist chronic fatigue syndrome clinics in the UK National Health Service between March 18, 2005, and Nov 28, 2008. We assessed mediation using the product of coefficients method with the 12 week measure of the mediators and the 52 week measure of the outcomes. The primary outcomes were fatigue measured by the Chalder fatigue scale and physical function measured by the physical function subscale of the SF-36. We included confounder covariates and used treatment by mediator interaction terms to examine differences in mediator-outcome relations by treatment group.
  
  
  RESULTS
  The largest mediated effect for both CBT and GET and both primary outcomes was through fear avoidance beliefs with an effect of larger magnitude for GET (standardised effects ×10, CBT vs APT, fatigue -1.22, 95% CI -0.52 to -1.97, physical function 1.54, 0.86 to 2.31; GET vs APT, fatigue -1.86, -0.80 to -2.89, physical function 2.35, 1.35 to 3.39). Increase in exercise tolerance (6 min walk distance) was a potent mediator of the effect of GET (vs APT, fatigue -1.37, 95% CI -0.76 to -2.21, physical function 1.90, 1.10 to 2.91), but not CBT.
  
  
  CONCLUSIONS
  Our main finding was that fear avoidance beliefs were the strongest mediator for both CBT and GET. Changes in both beliefs and behaviour mediated the effects of both CBT and GET, but more so for GET. The results support a treatment model in which both beliefs and behaviour play a part in perpetuating fatigue and disability in chronic fatigue syndrome.
  
  
  BACKGROUND
  UK Medical Research Council, Department of Health for England, Scottish Chief Scientist Office, Department for Work and Pensions, National Institute for Health Research (NIHR), NIHR Biomedical Research Centre for Mental Health at South London and Maudsley NHS Foundation Trust, and Institute of Psychiatry, Psychology, and Neuroscience, King's College London.
authors.affiliation: Academic Department of Psychological Medicine, King's College London, Weston Education Centre, London, UK. Electronic address: trudie.chalder@kcl.ac.uk.
authors.forename: Trudie
authors.initials: T
authors.lastname: Chalder
authors.affiliation: Department of Biostatistics, King's College London, London, UK.
authors.forename: Kimberley A
authors.initials: KA
authors.lastname: Goldsmith
authors.affiliation: Centre for Psychiatry, Wolfson Institute of Preventive Medicine, Barts and the London School of Medicine, Queen Mary University, London, UK.
authors.forename: Peter D
authors.initials: PD
authors.lastname: White
authors.affiliation: Psychological Medicine Research, Department of Psychiatry, University of Oxford, Oxford, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Sharpe
authors.affiliation: Department of Biostatistics, King's College London, London, UK.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Pickles
mesh_terms: D015673:Fatigue Syndrome, Chronic / Q000534:rehabilitation*; D006801:Humans; D012046:Rehabilitation / Q000379:methods; D016896:Treatment Outcome