• Rosalind S Parker, Gwyn N Lewis, David A Rice, and Peter J McNair.
• Health & Rehabilitation Research Institute, Faculty of Health and Environmental Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand; Department of Physiotherapy, Waitakere Hospital, Auckland 0650, New Zealand. Electronic address: roz.parker@aut.ac.nz.
• Brain Stimul. 2016 Jul 1; 9 (4): 488-500.

BackgroundChronic pain is characterised by maladaptive neuroplasticity in many systems, including the motor system. There is evidence that patients with chronic pain demonstrate altered corticospinal and intracortical excitability; however, findings are inconsistent and existing literature in this area has not been systematically reviewed.ObjectiveTo systematically review studies examining corticospinal and intracortical excitability using transcranial magnetic stimulation in people with chronic pain compared to healthy controls and to provide a meta-analysis of study outcomes.MethodsDatabases were searched for controlled studies evaluating corticospinal and intracortical excitability in chronic pain conditions. Outcome measure data were entered into separate meta-analyses and effect sizes calculated. A subgroup analysis based on the type of chronic pain population was also performed.ResultsForty-three studies were included, encompassing a pooled total of 1009 people with chronic pain and 658 control participants. Significant effect sizes (P < 0.05) indicated that in chronic pain populations the duration of the silent period and the extent of short-interval intracortical inhibition were both reduced and short-interval intracortical facilitation was enhanced. The subgroup analysis revealed that only the neuropathic pain group exhibited significant effect sizes for these outcome measures. Effect sizes for the remaining outcome measures were not significantConclusionsThere is evidence of motor cortex disinhibition in chronic pain populations, suggestive of a disruption in GABA-mediated intracortical inhibition. Disinhibition was more pronounced in populations with neuropathic pain. These findings provide new insights into the relationship between chronic pain and motor cortex excitability, which may have meaningful implications for the future treatment of chronic pain conditions.Copyright © 2016 Elsevier Inc. All rights reserved.

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