Predictors of outcome following treatment for chronic fatigue

We explored the role of baseline characteristics of 105 patientswho presented with fatigue in primary care in determining outcomefollowing either graded exercise or cognitive–behaviouraltherapy. Meeting the criteria for chronic fatigue syndromewas the most powerful predictor of poor outcome and this negativeeffect was enhanced by greater functional impairment or greaterperceived negative consequences, but was not further enhancedby both.

INTRODUCTION

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INTRODUCTION

We investigated predictors of outcome in a previously reported (McCrone et al, 2004; Ridsdale et al, 2004) group of patientswho presented to general practitioners (GPs) with fatigue. Wehypothesised that fatigue score following therapeutic interventionwith either cognitive–behavioural therapy (CBT) or gradedexercise would be predicted by baseline fatigue severity (includingchronic fatigue syndrome status and functional impairment),psychological morbidity and illness beliefs.

METHOD

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METHOD

The group was drawn from patients recruited to a multicentrerandomised trial comparing CBT with graded exercise for patientswith chronic fatigue in primary care (Ridsdale et al, 2004).Inclusion criteria were age 16–75 years; fatigue as a main or important problem lasting for 3 months or more; anda score of at least 4 on the fatigue questionnaire–bimodalscoring (Chalder et al, 1993). Further inclusion and exclusioncriteria are detailed in Ridsdale et al, 2004. Of the 123patients included, 60 were randomised to graded exercise therapy and 63 to CBT. This report describes the 105 patients (85%)who remained in the study at the 8-month follow-up.

Measures
Fatigue was measured with a Likert-scored scale (Chalder et al, 1993). Chronic fatigue syndrome status was determined using criteriadefined by Fukuda et al (1994): fatigue with a definite onset,of a minimum duration of 6 months, with substantial functionalimpairment, and four or more additional symptoms from a listof eight. Additional measures included scores on the HospitalAnxiety and Depression scale (Zigmond & Snaith, 1983);degree of functional impairment scored on the Work and SocialAdjustment Scale (WSAS; Marks, 1986); illness beliefs, includingperceived negative consequences (Weinman et al, 1996); andillness attributions (physical/psychological) (Powell et al, 1990). For more information on the measures used, see Ridsdale etal (2004). Patients performed a step test at baseline assessment(stepping on to a bench for 1 min). Patients were also askedto report whether they had previously consulted a doctor for an emotional problem, had been referred to a psychiatrist,or were members of a myalgic encephalomyelitis (ME) supportgroup. Information on prior psychological diagnoses and consultationfrequency was extracted from general practice records.

Analysis
Predictors of fatigue outcome were investigated using linearregression analysis. Univariate regression coefficients werecalculated for each of the 15 independent variables (10 continuous,4 binary and 1 categorical). The continuous variables are shownin Table 1. The binary variables were meeting criteria forchronic fatigue syndrome; past history of anxiety or depression;membership of an ME support group; and type of therapy. Thecategorical variable was duration of fatigue (five orderedcategories). Independent variables reaching a significance level of P40.05 were entered into a multiple regression model. Theresults of the regression analyses are shown as the mean increasein final fatigue associated with having v. not having the exposure(binary variables) or with each additional scale point (continuousvariables).

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Table 1 Initial scores on continuous predictor variables and their correlation with final fatigue

RESULTS

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RESULTS

The participants’ scores are shown in Table 1. Thirty-oneper cent (n=33) met chronic fatigue syndrome criteria, 5% (n=5)were members of an ME support group, and 60% (n=63) had a historyof psychological diagnosis. The dependent variable, final fatiguescore, was normally distributed (mean 15.03, skewness 0.137),with a significant improvement following therapy of 10.14 (s.d.=8.69)points (95% CI 8.46–11.82, skewness 0.209).

When entered in separate univariate regression analyses, sevenof the variables were associated with a higher final fatiguescore: greater initial fatigue (b=0.44; 95% CI 0.16–0.79);meeting chronic fatigue syndrome criteria (b=7.74; 95% CI 4.46–11.01);greater functional impairment (b=0.40; 95% CI 0.21–0.59);fewer steps performed (b=-0.25; 95% CI -0.49 to -0.01); higherdepression score (b=0.63; 95% CI 0.18–1.08); greater perceivednegative consequences (b=4.15; 95% CI 1.80–6.51); and membership of ME support group (b=8.79; 95% CI 1.12–16.46).

In a second model with these seven variables, only chronic fatiguesyndrome status (b=4.50; s.e.=2.02; 95% CI 0.49–8.51)contributed significantly (model R² 0.24, adjusted R²=0.19, F=4.36; P<0.001). Following this, six bivariate analyses that each included chronic fatigue syndrome status and oneof the other six variables showed that only functional impairment(R²=0.22, adjusted R²=0.20) and greater perceived negative consequences (R²=0.21, adjusted R²=0.19) added significantlyto the model when entered alongside chronic fatigue syndromestatus. When all three variables were entered simultaneouslyinto the model, it was not enhanced by a greater degree thanby adding functional impairment or greater perceived negative consequences alone (R²=0.22, adjusted R²=0.20).

DISCUSSION

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DISCUSSION

We expected to find that fatigue severity, illness beliefs,psychological state and physical fitness would affect outcome.In fact, chronic fatigue syndrome status, a known marker offatigue severity, was the most robust predictor of final fatiguefollowing therapy. Only three variables explained more than10% of the variance in final fatigue when considered alone:baseline chronic fatigue syndrome status (18%), functionalimpairment (14%) and perceived negative consequences (11%).Relationships between recovery and each of these variableshave been found previously for patients with fatigue in primaryand secondary care (Bentall et al, 2002; Chalder et al, 2003).Membership of an ME support group might also be important andhas been reported as being so in previous studies (Bentall et al, 2002), but the size of the subgroup in our study provided insufficientpower to support a relationship.

The results suggest that, individually, functional impairmentand greater perceived negative consequences add to the powerof chronic fatigue syndrome status to predict final fatigue,but add no more power when combined. This is partly explainedby the relatively high correlation observed between them, whichat 0.690 is larger than that between any of the other variables(0.656 between functional impairment and baseline fatigue;0.419 between chronic fatigue syndrome status and final fatigue).Chalder et al (2003) also found the latter two variables ofpredictive value, but did not find that chronic fatigue syndromestatus was associated with a poor outcome. The data presentedhere are the first to suggest that meeting criteria for thissyndrome is likely to predict a poor outcome following treatmentin primary care.

Levels of fatigue can fluctuate considerably between visits;our study deals with the information that would be availableto a GP at a single consultation. Any of the measures usedin predicting fatigue could have been repeated at subsequentvisits, and any predictive power would have been increased.

Patients with chronic fatigue syndrome are likely to have apoorer prognosis and may require a greater amount or a differenttype of therapy. In view of this, we believe that it will beuseful for GPs to know and apply the criteria for the syndromewhen they assess patients with fatigue in primary care. Itshould help them advise on prognosis and management.

ACKNOWLEDGMENTS

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ACKNOWLEDGMENTS

We thank the patients, GPs and their teams, therapists and manycolleagues who provided feedback at different stages, includingProfessors Peter White and Roger Jones. The study was supportedby a grant from the Linbury Trust.

REFERENCES

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