Journal of Psychiatry Spectrum (Jan 2025)
Efficacy of Transcranial Direct Current Stimulation on Cognitive Function in Dementia and Mild Cognitive Impairment Secondary to Neurodegenerative Etiology: A Systematic Review and Meta-Analysis
Abstract
Background: Dementia is a chronic progressive illness with significant impairment in a person’s functioning ability. The currently available treatment options for dementia are limited in modifying disease progression. Non-invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) are emerging as potential treatment options for cognitive as well as behavioral symptoms in dementia. The objective of this systematic review and meta-analysis is to assess the efficacy of tDCS on cognitive function in mild cognitive impairment (MCI) and dementia due to neurodegenerative disorders to provide an update on the existing evidence considering an increasing number of trials using tDCS. Methods: The study was conducted according to the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines with a prespecified protocol registered in PROSPERO (CRD42024503852). The study selection was made through a search on databases such as PubMed, Ovid MEDLINE, APA PsycInfo, and Cochrane trials registry and a gray literature search on ClinicalTrials.gov. All randomized controlled trials that have used tDCS as a standalone intervention for cognitive impairment were included in the present study. Risk of bias (RoB) was assessed by the Cochrane RoB2 tool. Meta-analysis of outcomes was performed using RevMan software version 5.4. Pooled estimates of standardized mean difference (SMD) and 95% confidence interval (CI) were obtained for global cognition (primary outcome) and other domain-specific cognitive outcomes. Results: A total of 24 studies were finally included in the review. Most of the studies had “some concerns” with regard to the overall RoB. A total of 164 subjects in the true tDCS group and 151 subjects in the sham tDCS groups out of eight studies were analyzed for global cognitive outcome, giving a pooled SMD (95% CI) of 0.80 (0.35, 1.26), giving an overall effect of Z = 3.45 (P < 0.001), with I2 value of 72%, favoring true tDCS. On a sub-group analysis, a significant improvement was noted in the Alzheimer’s dementia group but not MCI. Discussion: The study findings suggest that tDCS is effective in improving global cognition in participants with Alzheimer’s dementia but not MCI. Owing to a smaller number of studies, the domain-specific cognitive outcomes could not be assessed effectively. There was a wide heterogeneity in the included studies in terms of tDCS stimulation protocols.
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