Repetitive Transcranial Magnetic Stimulation as an Alternative Therapy for Cognitive Impairment in Alzheimer's Disease: A Meta-Analysis

Abstract

Background: Recent studies have indicated that repetitive transcranial magnetic stimulation (rTMS) could improve cognitive function in people with Alzheimer's disease (AD). Yet the results are inconclusive.

Objective: This meta-analysis aimed to evaluate recent rTMS studies conducted in mild to moderate AD patients.

Methods: PubMed, Embase, MEDLINE databases and Science Direct were searched for studies of rTMS treatment on AD patients with cognitive impairment published before February 2015. The relevant primary outcomes of cognition were extracted from those included studies. A crude standardized mean difference (SMD) with 95% confidence interval (CI) was calculated by using random effect models.

Results: Seven studies with a total of 94 mild to moderate AD patients were included in this meta-analysis. A significant overall rTMS treatment effect on cognition was found for all AD patients (p = 0.0008, SMD = 1.00, 95% CI = 0.41-1.58). Stratification analysis showed that this effect is stimulation frequency- and hemisphere-dependent. High frequency stimulation (>1.0 Hz) (p < 0.05) but not low frequency stimulation (≤1.0 Hz) (p > 0.05) was significantly effective in improving the cognition of AD patients. Further, rTMS stimulation on right dorsolateral prefrontal cortex (DLPFC) and bilateral DLPFC (p < 0.05), but not on the left DLPFC (p > 0.05) was significantly effective in improving cognitive function of AD patients. A significant effect was observed in the rTMS subgroup (p < 0.05), rather than in the rTMS+drug subgroup (p > 0.05).

Conclusion: This meta-analysis supports that high frequency rTMS stimulation on right- or bilateral-DLPFC has significant therapeutic effect on cognitive function in patients with mild to moderate AD. Due to small number of studies included, more well-controlled rTMS studies should be evaluated in AD patients in the future.

Keywords: Alzheimer’s disease; meta-analysis; mild to moderate cognitive impairment; repetitive transcranial magnetic stimulation.