AUTHOR=Oliveira Paloma Cristina Alves de , Araújo Thiago Anderson Brito de , Machado Daniel Gomes da Silva , Rodrigues Abner Cardoso , Bikson Marom , Andrade Suellen Marinho , Okano Alexandre Hideki , Simplicio Hougelle , Pegado Rodrigo , Morya Edgard 

TITLE=Transcranial Direct Current Stimulation on Parkinson's Disease: Systematic Review and Meta-Analysis

JOURNAL=Frontiers in Neurology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2021.794784

DOI=10.3389/fneur.2021.794784

ISSN=1664-2295

ABSTRACT=<p><bold>Background:</bold> Clinical impact of transcranial direct current stimulation (tDCS) alone for Parkinson's disease (PD) is still a challenge. Thus, there is a need to synthesize available results, analyze methodologically and statistically, and provide evidence to guide tDCS in PD.</p><p><bold>Objective:</bold> Investigate isolated tDCS effect in different brain areas and number of stimulated targets on PD motor symptoms.</p><p><bold>Methods:</bold> A systematic review was carried out up to February 2021, in databases: Cochrane Library, EMBASE, PubMed/MEDLINE, Scopus, and Web of science. Full text articles evaluating effect of active tDCS (anodic or cathodic) vs. sham or control on motor symptoms of PD were included.</p><p><bold>Results:</bold> Ten studies (<italic>n</italic> = 236) were included in meta-analysis and 25 studies (<italic>n</italic> = 405) in qualitative synthesis. The most frequently stimulated targets were dorsolateral prefrontal cortex and primary motor cortex. No significant effect was found among single targets on motor outcomes: Unified Parkinson's Disease Rating Scale (UPDRS) III – motor aspects (MD = −0.98%, 95% CI = −10.03 to 8.07, <italic>p</italic> = 0.83, <italic>I</italic><sup>2</sup> = 0%), UPDRS IV – dyskinesias (MD = −0.89%, CI 95% = −3.82 to 2.03, <italic>p</italic> = 0.55, <italic>I</italic><sup>2</sup> = 0%) and motor fluctuations (MD = −0.67%, CI 95% = −2.45 to 1.11, <italic>p</italic> = 0.46, <italic>I</italic><sup>2</sup> = 0%), timed up and go – gait (MD = 0.14%, CI 95% = −0.72 to 0.99, <italic>p</italic> = 0.75, <italic>I</italic><sup>2</sup> = 0%), Berg Balance Scale – balance (MD = 0.73%, CI 95% = −1.01 to 2.47, <italic>p</italic> = 0.41, <italic>I</italic><sup>2</sup> = 0%). There was no significant effect of single vs. multiple targets in: UPDRS III – motor aspects (MD = 2.05%, CI 95% = −1.96 to 6.06, <italic>p</italic> = 0.32, <italic>I</italic><sup>2</sup> = 0%) and gait (SMD = −0.05%, 95% CI = −0.28 to 0.17, <italic>p</italic> = 0.64, <italic>I</italic><sup>2</sup> = 0%). Simple univariate meta-regression analysis between treatment dosage and effect size revealed that number of sessions (estimate = −1.7, SE = 1.51, z-score = −1.18, <italic>p</italic> = 0.2, IC = −4.75 to 1.17) and cumulative time (estimate = −0.07, SE = 0.07, z-score = −0.99, <italic>p</italic> = 0.31, IC = −0.21 to 0.07) had no significant association.</p><p><bold>Conclusion:</bold> There was no significant tDCS alone short-term effect on motor function, balance, gait, dyskinesias or motor fluctuations in Parkinson's disease, regardless of brain area or targets stimulated.</p>