Associations Between Cognitive Performance and Pain in Chronic Fatigue Syndrome: Comorbidity with Fibromyalgia Does Matter

Background: In addition to the frequently reported pain complaints, performance-basedcognitive capabilities in patients with chronic fatigue syndrome (CFS) with and withoutcomorbid fibromyalgia (FM) are significantly worse than those of healthy controls. In variouschronic pain populations, cognitive impairments are known to be related to pain severity.However, to the best of our knowledge, the association between cognitive performance andexperimental pain measurements has never been examined in CFS patients.Objectives: This study aimed to examine the association between cognitive performance andself-reported as well as experimental pain measurements in CFS patients with and without FM.Study Design: Observational study.Setting: The present study took place at the Vrije Universiteit Brussel and the University ofAntwerp.Methods: Forty-eight (18 CFS-only and 30 CFS+FM) patients and 30 healthy controlswere studied. Participants first completed 3 performance-based cognitive tests designed toassess selective and sustained attention, cognitive inhibition, and working memory capacity.Seven days later, experimental pain measurements (pressure pain thresholds [PPT], temporalsummation [TS], and conditioned pain modulation [CPM]) took place and participants wereasked to fill out 3 questionnaires to assess self-reported pain, fatigue, and depressive symptoms.Results: In the CFS+FM group, the capacity of pain inhibition was significantly associatedwith cognitive inhibition. Self-reported pain was significantly associated with simple reactiontime in CFS-only patients. The CFS+FM but not the CFS-only group showed a significantlylower PPT and enhanced TS compared with controls.Limitations: The cross-sectional nature of this study does not allow for inferences ofcausation.Conclusions: The results underline disease heterogeneity in CFS by indicating that a measureof endogenous pain inhibition might be a significant predictor of cognitive functioning inCFS patients with FM, while self-reported pain appears more appropriate to predict cognitivefunctioning in CFS patients without FM.Key words: Chronic fatigue syndrome, cognitive function, cognitive inhibition, chronic pain,fibromyalgia, pain inhibition, pain-related cognitive impairment, working memory