• Richard E Harris, Pia C Sundgren, A D Craig, Eric Kirshenbaum, Ananda Sen, Vitaly Napadow, and Daniel J Clauw.
• University of Michigan, Chronic Pain and Fatigue Research Center, Ann Arbor, MI 48106, USA. reharris@med.umich.edu
• Arthritis Rheum. 2009 Oct 1; 60 (10): 3146-52.

ObjectiveCentral pain augmentation resulting from enhanced excitatory and/or decreased inhibitory neurotransmission is a proposed mechanism underlying the pathophysiology of functional pain syndromes such as fibromyalgia (FM). Multiple functional magnetic resonance imaging studies implicate the insula as a region of heightened neuronal activity in this condition. Since glutamate (Glu) is a major cortical excitatory neurotransmitter that functions in pain neurotransmission, we undertook this study to test our hypothesis that increased levels of insular Glu would be present in FM patients and that the concentration of this molecule would be correlated with pain report.MethodsNineteen FM patients and 14 age- and sex-matched pain-free controls underwent pressure pain testing and a proton magnetic resonance spectroscopy session in which the right anterior insula and right posterior insula were examined at rest.ResultsCompared with healthy controls, FM patients had significantly higher levels of Glu (mean +/- SD 8.09 +/- 0.72 arbitrary institutional units versus 6.86 +/- 1.29 arbitrary institutional units; P = 0.009) and combined glutamine and Glu (i.e., Glx) (mean +/- SD 12.38 +/- 0.94 arbitrary institutional units versus 10.59 +/- 1.48 arbitrary institutional units; P = 0.001) within the right posterior insula. No significant differences between groups were detected in any of the other major metabolites within this region (P > 0.05 for all comparisons), and no group differences were detected for any metabolite within the right anterior insula (P > 0.11 for all comparisons). Within the right posterior insula, higher levels of Glu and Glx were associated with lower pressure pain thresholds across both groups for medium pain (for Glu, r = -0.43, P = 0.012; for Glx, r = -0.50, P = 0.003).ConclusionEnhanced glutamatergic neurotransmission resulting from higher concentrations of Glu within the posterior insula may play a role in the pathophysiology of FM and other central pain augmentation syndromes.

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