Effectiveness of anodal transcranial direct current stimulation to improve muscle strength and motor functionality after incomplete spinal cord injury: a systematic review and meta-analysis

Study design Systematic review and meta-analysis. Objectives We aimed to investigate the effects of anodal transcranial direct current stimulation (tDCS) against sham on muscle strength and motor functionality after incomplete spinal cord injury (iSCI). Setting University of Sao Paulo, Brazil. Methods A preplanned protocol was registered (PROSPERO, CRD42016050444). Pubmed, Embase, Web of Science, Cochrane Central Library and BVS databases were searched independently by two authors up to March 2018. Cochrane Collaboration's Tool was used for the risk of bias assessments. Generic inverse variance and random-effects model were used to calculate pooled effect sizes (ES), 95% confidence intervals (CIs) and p-values in meta-analyses. Results Six randomized clinical trials met inclusion criteria (n = 78 iSCI individuals) and were included in the meta-analysis. Results showed a marginal significant pooled effect of active tDCS in improving motor functionality with a small ES (SMD = 0.26, 95% CI = -0.00 to 0.53, p = 0.05, I-2 = 0%). On the other hand, the pooled effect of active tDCS on muscle strength did not reach statistical significance, in parallel with a small ES (SMD = 0.35, 95% CI = -0.21 to 0.92, p = 0.22, I-2 = 0%) when compared with sham tDCS. No significant adverse events were reported. Conclusions Overall, there was a significant effect of tDCS in improving motor functionality following iSCI. However, a small ES and the marginal p-value suggest that these results should be interpreted with caution. Further high-quality clinical trials are needed to support or refute the use of tDCS in daily clinical practice.