Corticomotor Responses to Experimental, Acute, and Chronic Lower Limb Pain: A Systematic Review and Meta-Analysis.

Background: Corticomotor adaptations are believed to contribute to persistent pain. However, prior reviews have lacked sufficient data to adequately explore these adaptations in lower limb pain. This restricts the generalizability of existing research given the distinct functional and neurophysiological differences between upper and lower limb musculature. This research gap has prompted increasing exploration of corticomotor adaptations in response to lower limb pain. Accordingly, this systematic review aimed to synthesize literature investigating corticomotor changes in response to experimental, acute clinical, and chronic lower limb pain.

Methods: A comprehensive search of CINAHL, Ovid MEDLINE, PubMed, Scopus, and Web of Science was conducted. Transcranial magnetic stimulation (TMS) outcomes were separated into single-site assessments of corticomotor excitability over the motor cortical hotspot, assessments of inhibitory/facilitatory mechanisms, and corticomotor organization (mapping) outcomes. Critical appraisals were performed using the Downs and Black checklist and the TMS methodological checklist. Meta-analyses employed random effects models.

Results: Analyses of 18 studies found no consistent effects of lower limb pain on motor evoked potentials. However, motor threshold data indicated that corticomotor responses may vary by region and diagnosis. Results from TMS mapping studies revealed consistent shifts in CoG for representations of painful lower limb muscles, as well as increased overlap of adjacent representations. Map volume findings differed between experimental and clinical pain, suggesting temporal variation in adaptations.

Conclusion: This review highlights emerging evidence that corticomotor adaptations to lower limb pain are dynamic and region-specific. These findings lay the groundwork for future research into pain-related motor system plasticity.