Non-invasive cerebral and spinal cord stimulation for motor and gait recovery in incomplete spinal cord injury: systematic review and meta-analysis

Background Spinal cord injury (SCI) leads to gait impairment and loss of motor function and can be traumatic or non-traumatic in nature. Recently there has been important progress in the field of non-invasive central nervous stimulation, which can target the brain or spinal cord. In this review we aim to compare the effect of non-invasive cerebral and spinal cord stimulation on gait recovery and motor strength of lower limbs in subjects with SCI. Methods We conducted a search (from September 2022 until March 2024) using the PubMed, Cochrane, and PEDro databases, including all studies published since the year 2000. The protocol of the review followed PRISMA guidelines and only RCTs scoring above 5 on the PEDro scale were selected. Results A total of 12 RCTs with 341 participants were included. When all studies were pooled together, non-invasive central nervous system stimulation had significant effects on Lower Extremity Motor Scale (LEMS) score and gait speed. However, data was less apparent when subgrouped by type and level of stimulation. Repetitive transcranial magnetic stimulation (rTMS) showed large effect on LEMS, however transcranial direct current stimulation (tDCS) displayed a small effect on motor strength and gait speed. No meta-analysis could be performed for non-invasive spinal cord stimulation due to a lack of studies. Conclusions When all non-invasive stimulation techniques were pooled together, significant effects on motor strength and gait function were observed. However, subgroup analyses based on stimulation types and levels revealed a significant reduction in these effects, particularly when categorized by stimulation type (rTMS and tDCS). Furthermore, a meta-analysis could not be conducted for non-invasive spinal cord stimulation due to a lack of studies (only one study each on tsDCS and tSCS). Therefore, more randomized controlled trials are needed to evaluate neuromodulation interventions in spinal cord injury, particularly at the spinal cord level.