Persistent pain in the absence of structural pathology remains a challenging issue for clinicians. Besides the suffering from the pain itself, chronic ‘unexplained’ pain is often accompanied by other debilitating symptoms such as fatigue, sleep difficulties, dizziness, psychological symptoms, and cognitive problems among others. A growing body of scientific research underlines the involvement of a common pathophysiological mechanism of central sensitization (CS), commonly known as an hypersensitivity of the central nervous system, in overlapping chronic pain conditions such as chronic fatigue syndrome (CFS), fibromyalgia (FM) and chronic whiplash-associated disorders (WAD). One of the numerous common features seen in the majority of patients with chronic CS pain is the presence of debilitating cognitive dysfunctions. Cognitive complaints are some of the most frequent and significant contributors to social and occupational dysfunctions in these patients, thus having direct implications for their daily functioning.
The aim of this dissertation was to investigate possible associated and influencing factors of cognitive impairments in chronic CS pain conditions such as CFS, FM and chronic WAD. More specifically, the role of pain, health-related physical fitness and exercise were studied with regard to cognitive performance.
In various chronic pain conditions cognitive impairment has been linked to the continued presence of pain itself. Indeed, also in patients with FM and chronic WAD this phenomenon of pain-related cognitive impairment has been described. However, data regarding such an association in patients with CFS were inexistent. Based on the results of two cross-sectional studies, we demonstrated the presence of an association between pain and cognitive impairment in CFS patients with as well as without FM. Nonetheless, this relationship appeared to be different in both groups. More specifically, these studies revealed that efficiency of endogenous pain inhibition might be a significant predictor of cognitive performance in CFS patients with comorbid FM, while self-reported pain might be a predictor of cognitive performance in CFS patients without FM.
A positive relationship between physical and mental health has been observed in healthy individuals, and literature regarding this relation
in patients with chronic CS pain showed promising results as well. On the other hand, studies in CFS patients looking at relationships of
cognitive performance with aspects of health-related physical fitness and physical activity were lacking.
By means of two cross-sectional studies, we provided the first evidence for a positive relationship between cognitive performance and several aspects of health-related physical fitness in CFS patients with and without FM. However, no significant relationship between cognitive functioning and physical activity level was found in these patients.
The evidence for the positive relation between cognitive performance and health-related physical fitness in patients with chronic CS pain was supported by the findings of the very first study examining the influence of exercise on cognitive performance in patients with chronic WAD. Its results revealed that an acute aerobic exercise of moderate intensity is able to enhance certain aspects of cognitive performance (i.e. selective attention and choice reaction time) in patients with chronic WAD.
In addition, it was demonstrated that a significant relationship between performance-based and self-reported cognitive functioning exists in patients with CFS. This means that cognitive problems have to be taken seriously when reported by the patient. Therapy should therefore not merely target the patients’ return to physical but also to cognitive tasks. Together with the existing literature, the results of this dissertation suggest that physical exercise could be a possible tool for this purpose. On the other hand, the therapist has to keep in mind that these chronic pain disorders are characterized by the presence of CS, meaning that innocuous stimuli such as performing physical exercise can lead to an increase of pain and other symptoms and thus sustain the process of CS. Although physical exercise is essential for every CFS, FM, and chronic WAD patient, caution is advised when applying exercise therapy (interventions).