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.
FINDINGS: 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.
INTERPRETATION: 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.
FUNDING: 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.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Source: Chalder T, Goldsmith KA, White PD, Sharpe M, Pickles AR. Rehabilitative therapies for chronic fatigue syndrome: a secondary mediation analysis of the PACE trial. Lancet Psychiatry. 2015 Feb;2(2):141-52. doi: 10.1016/S2215-0366(14)00069-8. Epub 2015 Jan 28. https://www.ncbi.nlm.nih.gov/pubmed/26359750
Comment in
- Omission of data weakens the case for causal mediation in the PACE Trial. [Lancet Psychiatry. 2015]
- In non-blinded trials, self-report measures could mislead. [Lancet Psychiatry. 2015]
- What makes a difference in chronic fatigue syndrome? [Lancet Psychiatry. 2015]
- Doubts over the validity of the PACE hypothesis. [Lancet Psychiatry. 2015]
- Methods and outcome reporting in the PACE trial–Author’s reply. [Lancet Psychiatry. 2015]
- Methods and outcome reporting in the PACE trial. [Lancet Psychiatry. 2015]
- Post-exertional malaise in chronic fatigue syndrome. [Lancet Psychiatry. 2015]
COMMENTS
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Robert Courtney 2016 Feb 16 10:20 a.m
A study that uses questionable assumptions rather than empirical evidence leads to conclusions that stretch credibility.
Chalder et al. [1] used the “single mediation model” for their methodology, which is explained in detail in a book by MacKinnon [2]. Explaining the methodology MacKinnon says a temporal separation between variables must be observed (i.e. changes in mediating variable must occur before changes in the mediated variable) for a mediation effect to be empirically and robustly established.
Chalder et al. were working to this model and acknowledged that they failed to establish a clear temporal separation between variables, and therefore did not empirically establish a causal mediation effect: “Given the pattern of change in the mediators was similar to the pattern of change in the outcomes it is possible that the variables were affecting each other reciprocally”.
However, despite the lack of robust empirical evidence to support a mediation effect, the investigators concluded that they had established mediation effects, e.g: “Our main finding was that fear avoidance beliefs were the strongest mediator for both CBT and GET.”
The study’s conclusion relied upon an assumption that the investigators’ favoured hypothetical model of illness for ME/CFS has a robust empirical evidence base and is applicable to this study. The hypothesis is based upon the idea that symptoms and disability in ME/CFS are perpetuated by unhelpful or maladaptive illness beliefs, fear, and an avoidance of activity.
However, the prestigious National Academy of Medicine (formerly known as the Institute of Medicine) recently released a comprehensive report [3] into ME/CFS that rejected such a hypothetical model of illness, and unambiguously concluded that ME/CFS does not have a psychological or cognitive-behavioural basis, but is an organic illness that requires biomedical research.
Chalder et al. discussed the possibility that more frequent measurements may have potentially demonstrated a temporal separation between the variables, and therefore a mediation effect. However, this raises the possibility of whether changes in the primary outcome variables (self-report physical function and fatigue) may, in fact, have occurred before changes in the presumed mediator variables. Such an outcome would entirely contradict the investigators’ premature conclusions. According to MacKinnon [2] and Wiedermann et al. [4], unexpected outcomes should not be ruled out.
Chalder et al. concluded that symptoms and physical impairment, in ME/CFS patients, are mediated by activity avoidance and other factors. (e.g. This would mean that a decrease in activity would cause an increase in symptoms.) However, from a common sense point of view, this seems like rather a convoluted conclusion, and it seems more likely that increased symptoms would be the direct cause of activity avoidance in any illness, rather than vice versa. To conclude that activity avoidance causes fatigue (rather than fatigue being a direct cause of activity avoidance), is similar to concluding that a person has flu because they’ve taken a day off work, rather than the obvious conclusion that they’ve taken a day off work because they have flu.
In the case of fatigue, flu-like malaise and other symptoms of ME/CFS, it seems reasonable to consider the possibility that, as the symptoms fluctuate, patients may intuitively or rationally adapt their activity levels according to what is comfortable and safe. i.e. patients reduce activity levels because they are fatigued. The investigators have concluded that patients are fatigued because they have reduced activity levels.
Perhaps patients’ perspectives and insights would help clarify the issues but, unfortunately, patients were not consulted for this study.
References:
- Chalder T, Goldsmith KA, White PD, Sharpe M, Pickles AR. Rehabilitative therapies for chronic fatigue syndrome: a secondary mediation analysis of the PACE trial. Lancet Psychiatry 2015; 2: 141–52.
- MacKinnon DP. Introduction to Statistical Mediation Analysis. Taylor and Francis: New York 2008.
- IOM (Institute of Medicine). 2015. Beyond myalgic encephalomyelitis/chronic fatigue syndrome: Redefining an illness. Washington, DC: The National Academies Press. http://iom.nationalacademies.org/Reports/2015/ME-CFS.aspx
- Wiedermann W, von Eye A. Direction of Effects in Mediation Analysis. Psychol Methods 2015; 20: 221-44.
Tom Kindlon 2015 Sep 15 09:53 a.m.
Objective measures found a lack of improvement for CBT & GET in the PACE Trial: subjective improvements may simply represent response biases or placebo effects in this non-blinded trial
[Originally posted here: http://www.bmj.com/content/350/bmj.h227/rr-10]
This BMJ article and a flurry of articles in the lay media this week followed the publication in Lancet Psychiatry of an analysis of the mediators of change in the important PACE Trial, a chronic fatigue syndrome (CFS) trial which cost UK taxpayers £5 million[1,2]. What seems to have been lost in the coverage is that, although there were some modest improvements in the self-report measures, there was an almost complete absence of improvements in objectively measured outcomes for cognitive behavioural therapy (CBT) and graded exercise therapy (GET) compared to the control group (specialist medical care only (SMC)).
This is a non-blinded trial, where participants were told CBT and GET had previously been found to be effective in CFS and other conditions[3,4]: one way to look at the mediation results for subjective measures when there was a lack of objective improvements is that they may merely tell us how response biases and/or placebo effects are mediated[5].
The focus on subjective measures in some CFS studies was previously criticised in a systematic review published back in 2001 (long before the PACE Trial started)[6]. They suggested instead “a more objective measure of the effect of any intervention would be whether participants have increased their working hours, returned to work or school, or increased their physical activities.”
The model presented for cognitive behaviour therapy (CBT) in the PACE Trial manuals posits that the impairments and symptoms are reversible with the therapy[3,7]. However, the latest paper shows that fitness, as measured by a step test, didn’t improve following CBT[2]. An earlier PACE Trial publication reported that the addition of CBT to SMC did not result in an improvement in 6-minute walking test scores compared to SMC alone[8].
The PACE Trial was part funded by the UK Department of Work and Pensions, a rare move for them, presumably done due to an expectation that the therapies would improve measures of employment and levels of benefit receipt. However, again CBT brought about no improvement using objective measures, such as days of employment lost, levels of disability benefits received and levels of receipt of insurance payments[9].
These results are in line with earlier studies of CBT. For example, an analysis of three randomized controlled trials of CBT interventions for CFS found no improvement in objectively measured activity, despite participants reporting a reduction in (self-reported) fatigue and (sometimes) functional impairments[10]. Similar results were found in another uncontrolled trial where changes in objectively measured activity did not predict fatigue levels, and objectively measured activity on completion remained low compared to population norms[11]. An uncontrolled study found improvements in self-reported physical functioning and fatigue were reported despite a numerical decrease in (objectively measured) activity[12]. In another study, the level of self-reported cognitive impairment in CFS patients decreased significantly after CBT, however, cognition had not improved when it was measured objectively using neuropsychological test performance[13].
It is unsurprising that 15 sessions of CBT (and the associated homework exercises and management program) might alter how participants respond to self-report questionnaires. A PACE Trial manual itself says “the essence of CBT is helping the participant to change their interpretation of symptoms”: this could lead to altered or biased fatigue scores, one of the two primary outcome measures[14]. Also, one of the aims of CBT (for CFS) has been said to be “increased confidence in exercise and physical activity”[15]. The possible responses for the other primary outcome measure, the SF-36 physical functioning subscale, are “yes, limited a lot”, “yes, limited a little” and “no, not limited at all” to questions on a range of physical activities. Such responses could be easily be artificially altered following a therapy like CBT for CFS.
The results were not that different with the GET cohort in the PACE Trial. Again the manuals predicted that the impairments and symptoms are reversible using the intervention[4,15]. The model said there was no reason participants should not be able to get back to full functioning. Deconditioning was posited to be an important maintaining factor. However, GET did not result in an improvement in fitness, as measured by the step test. GET did result in a small improvement on the six minute walking test to a final distance of 379 metres, or 35 metres more than the SMC-only group[7]. However, as Knoop and Wiborg commented in an accompanying editorial in Lancet Psychiatry: “an increase in distance walked during a test situation without an increased fitness suggests that patients walk more because of a change in cognitive processes (eg, daring to do more or an increased self-efficacy with respect to activity), not because of a change in physiological capacity”[16]. The result remained very poor given that normative data would suggest a group of similar age and gender should walk an average of 644 or so metres[17]. The distance walked remained comparable to people with many serious conditions[18-21], and considerably worse than the distance walked by healthy elderly adults[22,23], despite the PACE trial cohort having a mean age of only 40[8]. Also, to be allowed entry into CFS research studies such as the PACE Trial one can not have a range of chronic illnesses so with genuine recovery one would expect results comparable to healthy people[8].
As with CBT, measures relating to employment showed no improvement following GET in days of work missed, which remained very high, nor a reduction in levels of benefits (financial support from the state) or payments from insurance companies[9].
These results are in line with an audit of Belgian rehabilitation centres for CFS offering CBT and GET[24-26]. Some improvements in subjective measures were found, but there was no improvement in the results of the exercise test and hours in employment actually decreased.
Probably the main contribution of the PACE Trial has been to add to a growing body of evidence that while CBT and GET for CFS have resulted in some changes on subjective measures, they haven’t lead to improvements on objective measures.
Competing interests: I am a committee member of the Irish ME/CFS Association and perform various types of voluntary work for the Association.
(continues)
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Tom Kindlon 2015 Sep 15 09:55 a.m.
(Contd.)
References:
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9 McCrone P, Sharpe M, Chalder T, Knapp M, Johnson AL, Goldsmith KA, White PD. Adaptive pacing, cognitive behaviour therapy, graded exercise, and specialist medical care for chronic fatigue syndrome: a cost-effectiveness analysis. PLoS One. 2012;7(8):e40808. doi: 10.1371/journal.pone.0040808
10 Wiborg JF, Knoop H, Stulemeijer M, Prins JB, Bleijenberg G. How does cognitive behaviour therapy reduce fatigue in patients with chronic fatigue syndrome? The role of physical activity. Psychol Med. 2010 Aug;40(8):1281-7. doi: 10.1017/S0033291709992212. Epub 2010 Jan 5.
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