• Björn Gerdle, Britt Larsson, Frida Forsberg, Nazdar Ghafouri, Linn Karlsson, Niclas Stensson, and Bijar Ghafouri.
• *Rehabilitation Medicine, Department of Medicine and Health Sciences (IMH) ‡Occupational and Environmental Medicine, Department of Clinical and Experimental Medicine (IKE), Faculty of Health Sciences, University of Linköping †Pain and Rehabilitation Centre §Centre of Occupational and Environmental Medicine, UHL, County Council, Linköping, Sweden.
• Clin J Pain. 2014 May 1;30(5):409-20.

BackgroundChronic widespread pain (CWP), including fibromyalgia syndrome (FM), is associated with prominent negative consequences. CWP has been associated with alterations in the central processing of nociception. Whereas some researchers consider CWP/FM as a central hyperexcitability pain condition, others suggest that the central alterations are maintained by peripheral nociceptive input. Microdialysis can be used in vivo to study muscle alterations in chronic myalgia.Aim: The aim of the study was to investigate the plasma and interstitial concentrations of metabolites and algesics in the trapezius muscle of women with CWP and in pain-free women (CON).Materials And MethodsSeventeen women with CWP and 24 CON went through a clinical examination and completed a questionnaire; the pressure pain thresholds in the upper and lower extremities were registered. Microdialysis was conducted in the trapezius muscle, and a blood sample was drawn. Muscle blood flow, interstitial muscle concentrations, and plasma concentrations of lactate, pyruvate, glutamate, glucose, and glycerol (not in the plasma) were determined.ResultsCWP patients had significantly increased interstitial muscle (P=0.02 to 0.001) and plasma (P=0.026 to 0.017) concentrations of lactate and glutamate. No significant differences existed in blood flow between CWP and CON. The interstitial concentrations-but not the plasma levels-of glutamate and lactate correlated significantly with aspects of pain such as pressure pain thresholds of the trapezius (R=0.22) and tibialis anterior (R=0.18) and the mean pain intensity (R=0.10) in CWP but not in CON.ConclusionsThe present study supports the suggestion that aspects of pain and central alterations in CWP/FM are influenced by peripheral tissue alterations.

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