University of Manchester
Royal Liverpool Broadgreen Trust
formerly University of Liverpool, UK
Correspondence: Professor Richard Bentall, Department of Psychology, University of Manchester, Coupland I Building, Oxford Road, Manchester M13 9PL, UK
Financial support from the Linbury Trust.
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ABSTRACT |
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Aims To identify predictors of response to psychological treatment for chronic fatigue syndrome.
Method Of 114 patients assigned to equally effective treatment conditions in a randomised, controlled trial, 95 completed follow-up assessments. Relationships between variables measured prior to randomisation and changes in physical functioning and subjective handicap at 1 year were evaluated by multiple regression.
Results Poor outcome was predicted by membership of a self-help group, being in receipt of sickness benefit at the start of treatment, and dysphoria as measured by the Hospital Anxiety and Depression scale. Severity of symptoms and duration of illness were not predictors of response.
Conclusions Poor outcome in the psychological treatment of chronic fatigue syndrome is predicted by variables that indicate resistance to accepting the therapeutic rationale, poor motivation to treatment adherence or secondary gains from illness.
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INTRODUCTION |
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METHOD |
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Treatment methods
The trial compared three different dosages (defined in terms
of therapist time and follow-up telephone contacts with the therapist) of an
educational intervention in which patients were taught evidence-based
physiological explanations of their symptoms and were encouraged to undertake
a home-based graded exercise programme. The minimum intervention
patients received two individual treatment sessions and two telephone
follow-up calls, plus access to a telephone helpline. The telephone
intervention patients received an additional seven planned follow-up
calls, and the maximum intervention patients received an
additional seven face-to-face sessions over 4 months.
Assessments
Clinical and demographic data collected from the patients prior to
recruitment to the trial included duration of illness, gender, receipt of
antidepressant therapy and sickness benefits, membership of a self-help group
(all assessed as yes/no variables) and belief in a physical cause of CFS
assessed by means of a four-point scale (definitely physical,
mainly physical, equally physical and
psychological/stress-related and mainly
psychological/stress-related) derived from a measure of CFS illness
beliefs developed by Wood et al
(1991). Self-rated validated
outcome measures sent by post were assessed before randomisation, and 3, 6 and
12 months after the beginning of treatment. Primary outcomes were measured on
the physical functioning sub-scale of the SF36, and on the fatigue scale
(Chalder et al, 1993:
range 0-11, scores greater than 3 indicate excessive fatigue). At baseline the
mean score for physical functioning of the treated patients was 16.0 and their
mean score on the fatigue scale was 10.28. Secondary outcome measures assessed
before treatment and at follow-up included the London Handicap Scale
(Harwood et al, 1994),
a multi-dimensional assessment of mobility, physical independence,
occupational functioning, social integration and economic self-sufficiency
which yields a global handicap score; the Hospital Anxiety and Depression
(HAD) scale (Zigmond & Snaith,
1983; scores above 10 indicate caseness); and a four-item sleep
problem questionnaire (Jenkins et
al, 1988).
Statistical analysis
Outcome data were available for 95 of the treated patients, representing
loss from the study of 17% of the sample. For those who dropped out, the last
recorded data point was carried forward prior to analysis. We analysed
predictors of improvement by multiple regression, entering all variables at
once, a method which is more conservative and less prone to type 1 errors than
the more commonly used stepwise method. As multiple regression allows one
variable to be included for every 10 participants, we had sufficient power to
include nine predictors (Kleinbaum et
al, 1988). Although treatment dose bore no relation to
outcome in our main outcome analysis at 1 year
(Powell et al, 2001)
we included it as a predictor in all analyses by coding dose as 1 (minimum
treatment), 2 (telephone treatment) and 3 (maximum treatment). Initial scores
on the dependent variables were included in the regression equations to
control for systematic relationships between initial scores and outcome.
Predictors were chosen on the basis of the hypotheses listed in the introduction. We therefore included the following binary variables: membership of a self-help group, living alone or as a lone parent, being in receipt of sickness benefits, and antidepressant therapy. Continuous variables included in the analysis were duration of illness, illness beliefs, and sleep disturbance scores. Depression and anxiety scores from the HAD scales were also included, but because these were highly correlated (Pearson r=0.56, P<0.001, one-tailed), they were summed into a single dysphoria variable to avoid the problem of multi-collinearity. Initial scores on these variables are shown in Tables 1 and 2. The mean physical functioning score of the members of the self-help groups was 14.29 compared with 16.38 for non-members, indicating that members were more impaired at the outset (t=2.80, P<0.01, 112 d.f.).
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RESULTS |
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Predictors of change in physical functioning scores
Our main outcome measure in the trial was change on the SF36 physical
functioning scale, which was approximately normally distributed, with an
average improvement of 8.83 points (s.d.=5.23, skewness0.557),
indicating that most of the patients who were followed-up improved. When this
was used as the dependent variable in the regression model, the equation was
highly significant (r2=0.38, F=6.29,
P<0.001). Standardised regression coefficients and significance
tests for each of the predictors are given in
Table 3. Apart from initial
physical functioning scores, poor response to treatment was predicted by (in
order of predictive power) dysphoria scores, membership of a self-help group,
and receipt of sickness benefit. Living arrangements (alone or as a single
parent), receipt of antidepressant therapy, sleep disturbance, duration of
illness, dose of treatment and surprisingly initial illness
beliefs did not add significantly to the model.
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Predictors of change in London Handicap Scale scores
Fatigue scores (both change and final), our second primary outcome measure,
deviated severely from the normal distribution and were unsuited to regression
analysis. Therefore, to assess the validity of the above findings, the
analyses were repeated using change scores on the London Handicap Scale, which
were normally distributed. The regression equation was again highly
significant (r2=0.38, F=6.13,
P<0.001). In addition to initial scores on the scale, predictors
of poor response on this scale were membership of a self-help group, receipt
of sickness benefit, belief in a physical cause of illness, and dysphoria
(Table 3).
Analyses excluding initial scores
It is difficult to interpret the theoretical significance of the observed
relationships between initial and change scores as these may simply reflect
the fact that those who were most ill had most opportunity to change. The
analyses were therefore repeated with final scores as the dependent variables.
These were less than ideal for analysis because they had highly non-normal
distributions with scores highly skewed towards maximum values (physical
functioning mean 24.74, skewness -0.96; London Handicap Scale mean 76.27,
skewness -0.22). None the less, the regression equation for final physical
functioning was significant (r2=0.34, F=5.16,
P < 0.001), the same three predictors were retained in the
equation, but initial physical functioning scores no longer predicted outcome.
Similarly, for final London Handicap Scale scores, a significant regression
equation was calculated (r2=0.39, F=6.59,
P < 0.001), with the same four predictors retained, and no
significant contribution to the model from initial London Handicap Scale
scores.
Supplementary analyses
In the above analyses we assumed that the scores of those who dropped out
had not changed from their last recorded data points. To test the impact of
this assumption, we repeated the main analyses assuming that all of those who
dropped out had done poorly by assigning them the relevant mean scores of the
untreated control group. For changes in physical functioning, dysphoria,
membership of a support group and receipt of state benefits remained
predictors. For changes in the London Handicap Scale scores, dysphoria,
membership of a support group, receipt of benefits, and physical illness
attributions were all retained. As a further check for the validity of our
assumptions, we repeated the analyses with all data from those who dropped out
excluded (leaving a sample size of 95). In this case, dysphoria and membership
of a support group remained predictors of changes in physical functioning, but
receipt of benefits was no longer a predictor. However, for changes in scores
on the London Handicap Scale, only membership of a support group remained as a
predictor.
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DISCUSSION |
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Variables predicting treatment response
The most robust predictors of poor treatment response were membership of a
support group and concurrent emotional difficulties. Although we found that
support group members were more ill than non-members on admission to the
study, this was controlled for in our regression analyses, and therefore
cannot explain the impact that membership had on outcomes. Receipt of benefits
and belief in exclusively physical causes of CFS were also predictors of poor
response in some of the analyses. These variables may be indicators of poor
motivation for treatment adherence. Individuals who are emotionally
distressed, who will experience financial difficulties when improving, and who
are initially sceptical about the value of psychological approaches, may have
difficulty persisting with a graded exercise programme.
Consistency with previous findings
Consistent with our findings, Sharpe et al
(1992) followed-up people with
CFS attending an infectious disease clinic and found that poor outcome was
associated with emotional disorder, belief in a viral illness and membership
of a self-help organisation (other predictors of poor response were limiting
exercise, avoiding alcohol and changing employment). In a 4-year follow-up of
patients taking part in an open, uncontrolled trial of psychological treatment
for CFS, Bonner et al
(1994) found that poor response
was predicted by emotional disorder and that there was also a trend for
physical illness beliefs to predict a poor response; however, no relationship
was found between response and membership of a support group. The current
finding that receipt of sickness benefit at the start of treatment is
associated with poor outcome is consistent with a report by Barsky & Borus
(1999) that disability payments
are associated with worse symptomatic outcome after medical treatment.
Mechanic (1986) reported that interest groups who adhere to particular theories of illness may play a part in reinforcing illness beliefs. In the presence of such a group, a personal problem becomes a shared social problem. Although there are undoubted psychological benefits from this kind of support (McCully et al, 1996), there have been reports that the advice dispensed by some CFS groups may have a negative effect on recovery, for example by advocating the avoidance of activity (Abbey, 1993; Surawy et al, 1995). It may be counterproductive to discourage patients from joining such groups, however; instead, clinicians and researchers should forge constructive alliances with support groups, to ensure that patients receive advice that is consistent and evidence-based. In this context, we should like to acknowledge that our work has been assisted by support groups in the Merseyside area, who have had an active role in ensuring that our treatment programme is now being offered as a routine National Health Service therapy.
Limitations of this study
The randomised clinical trial from which these data were taken had several
limitations, which should be noted. The Oxford criteria for CFS, used as an
entry criterion, are broader than the now widely used Centers for Disease
Control definition (Fukuda,
1994). More importantly, outcome was measured by self-report.
Although this had the advantage of minimising the possibility of researcher
bias in assessing outcome, it would have been better to have included an
objective measure of exercise capacity. None the less, it seems implausible
that these limitations can account for the results discussed here. In general,
the observation that an intervention designed to affect illness beliefs had
positive effects, coupled with the observation that variables indicative of
poor treatment motivation predicted poor outcome, is consistent with our
overall hypothesis that attitudinal factors play a part in maintaining CFS
symptoms.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication August 1, 2001. Revision received April 10, 2002. Accepted for publication April 17, 2002.
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