Summary of main findings
During the year following the consultation, a minority of the patients reported recovery within 4 months, while a substantial number of patients showed an unfavourable course. The combination of factors that best predicted the course of fatigue reflected different dimensions: demographics, fatigue characteristics, perceptions, general health, psychological, and social factors. This corresponds well with the concept that fatigue is a multidimensional problem. Consistent and significant predictors of an unfavourable outcome in both models were baseline severity of fatigue and patient expectations of chronicity.
Strengths and limitations of the study
Instead of measuring the outcome at one moment in time, the outcomes of repeated measurements during 1 year were combined to define a favourable or unfavourable course. This may have resulted in a more stable outcome, and thus have strengthened the results. Separate analyses were performed for patients with either a good or a poor outcome, because this provided information about relevant subgroups of patients, and may help GPs in their decision making with regard to management of the problem.
By assessing the relative contribution of a variety of potentially relevant prognostic factors, addressing somatic, psychological, and social problems, the multidimensional nature of the symptom was taken into account. Although some potential predictors may have been missed (for example, occupational factors or spiritual beliefs), the study included a variety of factors that can be measured by means of questionnaires in a large-scale observational cohort study. Clinical management could also account for variation in outcome. Although self-report data on treatment were collected, it was decided not to use this information in the prognostic models. In this observational study, confounding by indication would result in misleading information about the predictive value of management decisions.
Although the drop-out rate was low it was not possible to define the course of fatigue in each patient. It is unlikely, however, that this has strongly affected the composition of our prognostic models. Furthermore, notwithstanding the performance of the models, the results need to be validated in other populations of patients presenting with fatigue. Apart from perceived health, no factors were found that were positively associated with a fast recovery. However, the contribution of negative perceptions to prognosis would imply that positive (or neutral) perceptions would have a positive effect on the course of fatigue. Investigating (coping) behaviour, patterns of activity, and diet in future studies could reveal additional prognostic factors that are potentially modifiable and may provide alternative starting points for the development of interventions.
Comparison with existing literature
Baseline severity of fatigue has been found to be a prognostic factor in other studies in primary care,21 and in the community.9,22,23 Duration of fatigue was found to be a prognostic indicator of outcome in other studies,6,24 but was not retained in the present study model; neither was localisation of fatigue. Both characteristics are apparently strongly related to severity, but their contribution was not significant in combination with fatigue severity.
Rather than fatigue duration at baseline, patient expectations of chronicity significantly predicted an unfavourable course of fatigue in both models. Similar results have been found in a previous study in primary care for poor fatigue outcome after 6 months.25 Furthermore, more personal control or self-efficacy has been shown to be associated with a better prognosis in fatigued employees on sick leave,26 and patients with chronic fatigue syndrome,27 which may indicate that more personal control can result in more positive expectations regarding the course of the fatigue and, subsequently, in better outcomes.
The prognostic value of patient expectations might explain why psychological symptoms were not retained in the models. Previous studies that reported associations of psychological symptoms with fatigue outcome did not measure illness-related perceptions.21,28 Likewise, contrary to findings from other studies,9,25–27 patient attributions were not retained in this study's models. This might be partly explained by the fact that patients often have mixed attributions; an exclusively somatic illness attribution may have more predictive value than the presence of a psychological attribution. More importantly, patient attributions may be related to expectations of chronicity. These catastrophising perceptions were consistently retained in both models, and were apparently more important in predicting outcome in this study's population.
Apart from psychological symptoms, the number of other physical symptoms and pain intensity were also related to a poor outcome, whereas better perceived health was related to a favourable outcome. These results are in line with the results of studies among employees with fatigue.26,29
Female sex, providing informal care, and more (severe) prolonged difficulties were included in the combination of factors that were inversely associated with a fast recovery. This seems to indicate a negative influence of higher levels of external demands. Caring for young children has been reported to be associated with fatigue in a cross-sectional nationwide study,30 and can be a sex-specific indication of more responsibilities, but such an association was not found longitudinally. However, although less frequent in the present study population, providing informal care for other (ill or older) adults was a significant predictor. It could be hypothesised that taking care of children is generally a choice or a planned responsibility that takes place in another phase of life, and therefore might be perceived as less distressful or tiring.
A majority of 82% of the participants in this study reported that they experienced prolonged difficulties, and 17% experienced severe difficulties in at least one area. The associations of prolonged difficulties and social support with outcome are in line with studies among patients with chronic fatigue syndrome, showing that negative interactions or insufficient support contribute to the persistence of symptoms,31 and that negative or serious difficulties were more frequent in the months preceding the onset of chronic fatigue syndrome.32,33 Furthermore, enjoying daily activities was univariately associated with a positive outcome in the current study, while the number of life events was not associated with a negative outcome. These findings would support the notion that perceived quality or intensity of activities or events may be more important than their number in contributing to the (im)balance between perceived demands and resources in patients with fatigue.
