Transcranial Direct Current Stimulation for Treatment of Alzheimer’s Disease: A Systematic Review of Randomized Clinical Trial

Introduction: Alzheimer’s disease (AD) is a neurodegenerative pathology manifested by cognitive impairment and behavioral derangement. Transcranial Direct Current Stimulation (tDCS) as non-invasive and safe neuromodulation technique has shown promising effects in different neuropsychiatric disorders. Similarly, tDCS has recently shown potential therapeutic outcomes in AD. The present study aims to systematically review the therapeutic efficacy of tDCS in patients with AD. Method: The databases of PubMed (1970-2017), Web of Sciences (1970-2017), and Google Scholar (1980-2017) were searched using the set terms "tDCS" OR "transcranial direct current stimulation" AND "Alzheimer’s disease" OR "AD" AND "treatment". The search engine Trip Database was used and the date of last search was August 30, 2017. The retrieved records were reviewed Independently by two authors. Results: Seven studies were obtained with a total of 185 patients who met the inclusion criteria. Evaluating the results, 4 studies supported the possible efficacy of the therapy versus 3 that did not find statistically significant differences compared with the placebo groups. Anodal tDCS over frontal cortex, particularly left dorsolateral prefrontal cortex and temporal cortex, showed therapeutic efficacy in AD. Conclusion: Further studies are needed to determine effective protocols and clinical efficacy of tDCS for AD treatment. However, the current evidence from clinical trials encourages further research to investigate anodal tDCS as an adjuvant treatment for patients with AD.