Original ArticleThe persistence of fatigue in chronic fatigue syndrome and multiple sclerosis: Development of a model
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.
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