Transcranial Direct Current Stimulation Post-Stroke Upper Extremity Motor Recovery Studies Exhibit a Dose–Response Relationship

• Published in: Brain stimulation Vol. 9; no. 1; pp. 16 - 26
• Main Authors: Chhatbar, Pratik Y., Ramakrishnan, Viswanathan, Kautz, Steven, George, Mark S., Adams, Robert J., Feng, Wuwei
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.01.2016
• Subjects: Aged; Dose–response relationship; Hedge's g; Humans; Meta-analysis; Meta-regression; Motor recovery; Neurology; Recovery of Function; Stroke; Stroke - therapy; Stroke Rehabilitation; tDCS; Transcranial Direct Current Stimulation; Upper Extremity - physiology; Meta-regression; Stroke; Hedge's g; tDCS; Transcranial direct current stimulation; Motor recovery; Dose–response relationship; Meta-analysis
• ISSN: 1935-861X; 1876-4754; 1876-4754
• DOI: 10.1016/j.brs.2015.09.002

•Transcranial direct current stimulation (tDCS) shows dose-dependent effect in post-stroke motor recovery.•Meta-analysis of tDCS stroke recovery studies discovered a dose-response relationship in motor improvement measured by FM-UE scale. Pad size, charge density and current density are correlated with the FM-UE change scores, but current amplitude is not. Effect size is relatively larger in subjects with chronic stroke when compared with acute stroke. Bihemispheric montage seems to offer a larger effect size in post-stroke motor recovery.•Bihemispheric montage with anode on ipsilesional side and cathode on contralesional side also seems to offer a large effect size in post-stroke motor recovery. However, these results might be confounded by the fact that all the studies that used the bihemispheric montage recruited subjects with chronic stroke.•Inverse-variance-based meta-regression shows that pad size, charge density and current density are correlated with the FM-UE change scores after tDCS therapy. Transcranial direct current stimulation (tDCS) has shown mixed results in post-stroke motor recovery, possibly because of tDCS dose differences. The purpose of this meta-analysis was to explore whether the outcome has a dose–response relationship with various dose-related parameters. The literature was searched for double-blind, randomized, sham-controlled clinical trials investigating the role of tDCS (≥5 sessions) in post-stroke motor recovery as measured by the Fugl-Meyer Upper Extremity (FM-UE) scale. Improvements in FM-UE scores were compared between active and sham groups by calculating standardized mean differences (Hedge's g) to derive a summary effect size. Inverse-variance-weighted linear meta-regression across individual studies was performed between various tDCS parameters and Hedge's g to test for dose–response relationships. Eight studies with total of 213 stroke subjects were included. Summary Hedge's g was statistically significant in favor of the active group (Hedge's g = 0.61, p = 0.02) suggesting moderate effect. Specifically, studies that used bihemispheric tDCS montage (Hedge's g = 1.30, p = 0.08) or that recruited chronic stroke patients (Hedge's g = 1.23, p = 0.02) showed large improvements in the active group. A positive dose–response relationship was found with current density (p = 0.017) and charge density (p = 0.004), but not with current amplitude. Moreover, a negative dose–response relationship was found with electrode size (p < 0.001, smaller electrodes were more effective). Our meta-analysis and meta-regression results suggest superior motor recovery in the active group when compared to the sham group and dose–response relationships relating to electrode size, charge density and current density. These results need to be confirmed in future dedicated studies.