• Nicholas Jacob Snow, Megan Christine Kirkland, Matthew Bruce Downer, Hannah Margaret Murphy, and Michelle Ploughman.
• Recovery and Performance Laboratory, Faculty of Medicine, Memorial University of Newfoundland & Labrador, St. John's, NL, Canada.
• Medicine (Baltimore). 2022 Nov 18; 101 (46): e31774e31774.

BackgroundChronic noncancer pain is a global public health challenge. It is imperative to identify biological markers ("biomarkers") to understand the mechanisms underlying chronic pain and to monitor pain over time and after interventions. Transcranial magnetic stimulation (TMS) is a promising method for this purpose.ObjectivesTo examine differences in TMS-based outcomes between persons with chronic pain and healthy controls (HCs) and/or before versus after pain-modulating interventions and relationships between pain measures and TMS outcomes; To summarize the neurophysiological mechanisms underlying chronic pain as identified by TMS.MethodsWe searched the PubMed database for literature from January 1, 1985, to June 9, 2020, with the keywords "pain" and "transcranial magnetic stimulation." Eligible items included original studies of adult human participants with pain lasting for ≥ 6 months. We completed a narrative synthesis of the study findings stratified by chronic pain etiology (primary pain, neuropathic pain, and secondary musculoskeletal pain).ResultsThe search yielded 1265 records. The final 12 articles included 244 patients with chronic pain (192 females, aged 35-65 years) and 169 HCs (89 females, aged 28-59 years). Abnormalities in TMS outcomes that reflect GABAergic and glutamatergic activities were associated with many of the disorders studied and were distinct for each pain etiology. Chronic primary pain is characterized by reduced intracortical inhibition and corticospinal excitability, chronic neuropathic pain shows evidence of increased excitation and disinhibition, and chronic secondary musculoskeletal pain involves low corticospinal excitability.DiscussionTMS could be a useful tool for delineating the neurophysiological underpinnings of chronic pain syndromes.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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