Original Article
The persistence of fatigue in chronic fatigue syndrome and multiple sclerosis: Development of a model

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Abstract

The cause of chronic fatigue syndrome (CFS) is unknown. With respect to factors perpetuating fatigue, on the other hand, a model has been postulated in the literature in which behavioral, cognitive, and affective factors play a role in perpetuating fatigue. In the present study, this hypothesized model was tested on patients with CFS and on fatigued patients with multiple sclerosis (MS). The model was formulated in terms of cause-and-effect relationships and an integral test of this model was performed by the statistical technique, “structural equation modeling,” in 51 patients with chronic fatigue syndrome and 50 patients with multiple sclerosis matched for age, gender, and education. Attributing complaints to a somatic cause produced low levels of physical activity, which in turn had a causal effect on fatigue severity. Depression had to be deleted from the model. Sense of control over symptoms and focusing on bodily symptoms each had a direct causal effect on fatigue. The model showed an excellent fit for CFS patients, but was rejected for MS patients. Therefore, a new model for MS patients had to be developed in which sense of control had a causal effect on fatigue. In the MS model, no causal relationship was found between the physical state as measured by the Expanded Disability Status Score (EDSS) and fatigue or functional impairment. The present study shows that cognitive and behavioral factors are involved in the persistence of fatigue. Treatment should be directed at these factors. The processes involved in the subjective experience of fatigue in CFS were different from the processes related to fatigue in MS.

Introduction

Doctors dealing with patients with chronic fatigue syndrome (CFS) encounter significant problems and uncertainties: no physical cause can be established; no scientifically sound diagnostic test is available; and physical treatment is lacking. Considering these uncertainties many doctors are reluctant to make the diagnosis of CFS. Patients, on the other hand, are very persistent in seeking a diagnosis and a somatic explanation for their complaints.

The etiology of CFS is unknown. With respect to factors perpetuating complaints a model has been proposed in the literature, in which behavioral, cognitive, and affective factors perpetuate fatigue 1, 2, 3. According to this model, patients with CFS tend to avoid physical activity because in their view activity causes symptoms, such as fatigue and myalgia. This avoidance behavior, in fact, leads to more symptoms through physical deconditioning. In addition, these patients attribute complaints to a somatic cause and show strong resistance to psychosocial explanations 4, 5, 6, 7. Attributing complaints to an organic cause may reinforce the idea that physical activity is harmful and result in avoidance of physical activity. Attributing complaints to a somatic cause may also lead to low sense of control over symptoms, which in turn may produce mood disorder. Because depressed patients are known to be inactive, depression may contribute to producing low levels of physical activity. Depression may also produce fatigue directly [1].

Support for this model can be found in prospective studies and cognitive-behavioral treatment (CBT) programs 2, 7, 8, 9, 10, 11. These studies, however, can provide only circumstantial evidence, as the model was not tested integrally, and because these studies were not specifically concerned with evaluating the causal direction of relationships. Also, one of the reported CBT treatment programs was uncontrolled [2].

In the present study, an integral test of this model was performed using the statistical technique called “structural equation modeling,” also referred to as “causal modeling.” This technique is often used to test a theory about relationships between theoretical constructs [12]. These analyses improve the ability to make causal inferences about these relationships from nonexperimental data [13].

In a previous study, we found a close relationship between fatigue, on the one hand, and sense of control and focusing on bodily symptoms on the other [14]. In addition, in a longitudinal study of our research group we found that sense of control was a powerful predictor of fatigue severity and chronicity [7]. These findings are not specified in the hypothesized model. Therefore, after testing of the hypothesized (initial) model we attempted to extend the model with respect to these findings.

In developing a model for CFS patients, patients with multiple sclerosis (MS) are a useful comparison group, because, in MS, fatigue is a frequent and prominent symptom 14, 15, 16. In a previous study we performed a detailed multidimensional assessment of CFS patients and fatigued MS patients, measuring cognitive, emotional, behavioral, and social functioning [14]. We found similar profiles on physical activity, depression, causal attributions, and sense of control over symptoms in CFS and MS. To evaluate the specificity of the final model to CFS, the model was also tested on data from patients with MS.

Section snippets

Subjects

Fifty-one patients with CFS fulfilling criteria for CFS [17] and 50 patients with a clinically definite diagnosis of MS [18] who reported fatigue (chronic progressive course: N=19; relapsing remitting course: N=31) participated in this study. Mean Expanded Disability Status Score (EDSS) [19] was 2.8 (range 1–6). Both patient groups were similar with respect to age, gender, educational level, and duration of complaints (see Table I). All patients participating in this study received a full

Development of a model for CFS patients

In Table II the correlation matrix is presented. Testing and modification of the model was a multistage process. Results for each stage are presented in Table III.

Discussion

The present study developed a model for factors involved in the perpetuation of fatigue in CFS. This model showed a close fit to the underlying data. From this model it is clear that psychological factors are involved in the perpetuation of fatigue in CFS.

In accordance with the model outlined in the Introduction, in CFS, attributing complaints to a somatic cause had a direct causal effect on physical activity level, which in turn had a direct causal effect on fatigue. In a longitunal study of

Acknowledgements

Acknowledgments—This study has been supported in part by Stichting Vrienden MS Research (Grant 91-89 MS). We are indebted to E. H. W. Damhuis, J. C. J. M. Walk, and S. T. F. M. Frequin for their help in data collection.

References (31)

  • A. Wilson et al.

    Longitudinal study of outcome of chronic fatigue syndrome

    BMJ

    (1994)
  • D. Bonner et al.

    Chronic fatigue syndromea follow-up study

    J Neurol Neurosurg Psychiatry

    (1994)
  • M. Sharpe et al.

    Cognitive behaviour therapy for chronic fatigue syndromea randomized controlled trial

    BMJ

    (1996)
  • K. Jöreskog et al.

    LISREL 8structural equation modeling with the SIMPLIS command language

    (1993)
  • P.M. Bentler

    Multivariate analysis with latent variablescausal modeling

    Ann Rev Psychol

    (1980)
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