The effects of transcranial direct current stimulation on upper-limb function post-stroke: A meta-analysis of multiple-session studies.

Objective: To systematically review how patient characteristics and/or transcranial direct current stimulation (tDCS) parameters influence tDCS effectiveness in respect to upper limb function post-stroke.
Methods: Three electronic databases were searched for sham-controlled randomised trials using the Fugl-Meyer Assessment for upper extremity as outcome measure. A meta-analysis and nine subgroup-analyses were performed to identify which tDCS parameters yielded the greatest impact on upper limb function recovery in stroke patients.
Results: Eighteen high-quality studies (507 patients) were included. tDCS applied in a chronic stage yields greater results than tDCS applied in a (sub)acute stage. Additionally, patients with low baseline upper limb impairments seem to benefit more from tDCS than those with high baseline impairments. Regarding tDCS configuration, all stimulation types led to a significant improvement, but only tDCS applied during therapy, and not before therapy, yielded significant results. A positive dose-response relationship was identified for current/charge density and stimulation duration, but not for number of sessions.
Conclusion: Our results demonstrate that tDCS improves upper limb function post-stroke. However, its effectiveness depends on numerous factors. Especially chronic stroke patients improved, which is promising as they are typically least amenable to recovery.
Significance: The current work highlights the importance of several patient-related and protocol-related factors regarding tDCS effectiveness.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2021 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)