Evidence for generalized hyperalgesia in chronic fatigue syndrome: a case control study

Several studies provided evidence for generalized hyperalgesia in fibromyalgia or whiplash-associated disorders. In chronic fatigue syndrome, however, pain is a frequently reported complaint, but up to now, evidence for generalized hyperalgesia is lacking. The aim of this study is to examine whether the pressure pain thresholds (PPTs) at both symptomatic and asymptomatic sites differ in chronic fatigue syndrome (CFS) patients with chronic pain, compared to healthy controls. Therefore, 30 CFS patients with chronic pain and 30 age- and gender-matched healthy controls indicated on a Margolis Pain Diagram where they felt pain lasting longer than 24 h in the past 4 weeks. After completing a test battery of questionnaires evaluating pain cognitions, functional status and symptomatology, a blinded researcher assessed PPTs bilaterally at seven non-specific sites on both trunk and extremities. PPTs were compared for the two complete groups. In addition, PPTs of patients and controls who did not report pain in a respective zone were compared. PPTs of the patients were significantly lower (p < 0.001) compared to those of the control group, also when pain-free samples per zone were compared (p < 0.001). The mean PPT was 3.30 kg/cm² in all CFS patients and 8.09 kg/cm² in the controls. No confounding factors responsible for the observed differences, as, e.g., catastrophizing and depression, could be revealed. These findings provide evidence for the existence of hyperalgesia even in asymptomatic areas (generalized secondary hyperalgesia). The generalized hyperalgesia may represent the involvement of a sensitized central nervous system.