1. Introduction
Chronic fatigue syndrome (CFS) is a chronic illness characterized by post-exertional malaise, cognitive dysfunction, unrefreshing sleep, and other symptoms [
1]. While 88 abnormal gene expressions have been identified in patients with CFS, the precise etiology remains unclear [
2]. Furthermore, research suggests that few patients completely recovery, as Cairns and Hotopf [
3] found fewer than 10% of individuals return to their premorbid level of functioning. In spite of the debilitating nature of this illness, Looper and Kirmayer [
4] found that patients with CFS perceived more stigma than patients with other chronic conditions such as Fibromyalgia or irritable bowel syndrome. The stigma associated with CFS creates barriers for access to care [
5].
For individuals with CFS, there have been conflicting findings regarding how duration of illness affects symptoms and disability. It is possible that the early stages of this illness differ from later stages. Fennel [
6] has been suggested that individuals experience a “crisis phase” shortly after becoming ill. This crisis phase results from the loss of control in their lives as well as loss of resources such as work status [
7]. Fennell [
6] proposed that over time, patients learn better ways of dealing with their symptoms. In support of this, Jason
et al. [
8] found that despite high levels of impairment, over time, individuals living with CFS may learn strategies to pace themselves to accommodate to their illness [
8]. Jason and colleagues [
8] have found that helping patients conserve appropriate energy expenditures in coordination with available energy can help patients better cope with this illness.
Still, it is unclear whether those who have been ill for longer periods have a different health status from those who have been ill for briefer periods of time. For example, several researchers [
9,
10] have found that a longer illness duration predicts worse outcomes. Likewise, Friedberg, Dechene, McKenzie, and Fontanetta [
11] found that individuals who have had the illness for a longer period of time have significantly higher illness severity than those with shorter illness duration. Specifically, those who have had CFS for ten years or more had worse cognitive functioning than those who had been sick for seven years or less. Furthermore, van der Werf and colleagues [
12] found that patients with an illness duration of two years or longer reported more concentration problems, greater fatigue, and more functional disability than patients with a shorter illness duration.
However, others have found different results. For example, Hornig
et al. [
13] found distinct alterations in plasma immune signatures among patients with CFS with an illness duration less than three years that were not present in patients with an illness duration three years or longer. More specifically, patients with CFS with a short illness duration had increased amounts of many different types of cytokines in comparison with those with a longer illness duration. In addition, Matthews and Komaroff [
14] found that physical functioning tended to improve over time for many individuals with CFS.
Still others have not found differences in those with different illness durations. For example Wilson and colleagues [
15] did not find illness duration to predict patient outcome, and Hill, Tiersky, Scavalla, and Natelson [
16] found that illness outcome was not predicted by length of illness. Similarly, Brown, Brown and Jason [
17] found no difference in functioning between those with an illness duration of two years or longer and those with an illness duration shorter than two years. In addition, Santamarina-Perez
et al. [
18] found that cognitive functioning in patients who were sick for more than four years did not differ from patients who were sick less than one year. The reasons for these discrepant findings are unclear, but different ages of patients might have influenced these findings.
A patient’s age may contribute to differences in patient functionality and symptomatology [
19]. Joyce, Hotopf, and Wessely [
20] found that older age predicts a poorer CFS prognosis. In a prospective, longitudinal study, Jason
et al. [
21] found that that those that recovered over time from CFS were significantly younger than those that developed the illness. Loge, Ekeberg, and Kaasa [
22] found significantly higher fatigue scores in older individuals with CFS compared to younger individuals with CFS, which was also found by Song, Jason, and Taylor [
23].
The association between illness duration and patient age, with illness severity and symptomatology for individuals with CFS is unclear. Prior CFS research has focused either upon the relationship of illness duration on illness severity or the relationship of age on illness severity. However, studies have not examined the overlapping effects of both illness duration and age on patient outcomes. The current study investigated the association between illness duration and patient age on measures of functionality and symptomatology. The conflicting findings in the literature on these issues of age and duration of illness make it difficult to develop testable hypotheses in this exploratory study.
3. Discussion
The goal of this study was to examine the effects of age and illness duration on patient functionality and symptoms. Our major finding is that both age and duration of illness needs to be taken into account when understanding the effects of these variables on functioning and symptoms. We found that the younger/shorter illness duration group showed statistically higher levels of vitality than the younger/longer illness duration group. In addition, older patients with an illness duration of over 10 years have significantly higher levels of mental health functioning than the three other groups. For symptoms, the younger/longer illness duration group had significantly worse immune and autonomic domains than the older/longer illness group. In addition, the younger patients with a longer illness duration displayed greater autonomic and immune symptoms in comparison to the older group with a longer illness duration.
Findings indicated that people with CFS who were under the age of 55 with an illness duration of fewer than ten years had greater vitality than those who were similarly aged but had been ill longer. As the illness duration increased, younger individuals’ vitality deteriorated. It is possible that individuals with CFS may lose vitality over time due to worse physical functioning as it becomes more challenging for them to do functional tasks as the illness progresses. This finding supports prior research that a longer illness duration suggests greater illness severity [
11]. This difference was not found in the older patient group, which suggests the difference in vitality may be unique to younger individuals with CFS.
The older individuals with a longer illness duration indicated the best mental health functioning over the other groups. Those with a longer illness duration may have learned more effective coping skills such as planning and acceptance compared to the shorter illness duration group [
17]. This supports previous findings that patients with CFS endure a “crisis” stage early in their illness [
6], where they experience emotional distress and may be overwhelmed by the challenges of this debilitating illness [
33].
Moreover, older individuals with a longer illness duration reported better autonomic and immune scores than young individuals with a longer illness duration. The older patient group with a long illness duration also reported better neuroendocrine scores than the young patient group with a shorter illness duration. These differences support Chou’s [
19] prior research in that a patient’s age may contribute to patient symptomatology. This may help explain why older individuals experience greater levels of mental health functioning since they indicated better symptom scores than the other patient groups.
There are limitations to this study. The sample was predominately white and thus the findings may not be generalizable to a more diverse patient population. A prior study has shown that CFS does include many from African American and Latino populations [
34], but more tertiary care recruitment efforts have identified less diversity among samples. Future studies need to include more diverse populations to investigate possible cultural differences.
