Transcranial direct current stimulation effects in late life depression: A meta-analysis of individual participant data

Background: Late life depression (LLD) refers to major depressive disorder (MDD) in adults over 65 years. LLD is associated with high morbidity and poor treatment outcomes. Transcranial direct current stimulation (tDCS) is a novel treatment for MDD. Efficacy in LLD though is unclear. Our aim was to investigate tDCS efficacy by pooling randomised controlled trials (RCT) in an individual participant data meta-analysis. Methods: Databases were searched for sham controlled RCTs of tDCS in MDD and bipolar depression. Individual participant data (IPD) were requested. Primary outcome was change in depressive symptoms. Bayesian multilevel modelling meta-analysis was conducted with individual participants nested within studies. Results: 6 RCTs were eligible, consisting of 43 participants (22 women), mean age 69.2 years. Active anodal tDCS over left dorsolateral prefrontal cortex (n = 19) was associated with an improvement in depressive severity, effect size 0.14 (95% credible interval [-0.44;0.15]) as compared to sham tDCS, which was not statistically significant. There was an 82% probability that tDCS treatment has a modest but non-null effect in improving depressive symptoms. Acceptability was high with no significant differences in discontinuation rates between active and sham groups. Limitations: The total sample size was small, limiting power. Discussion: In LLD, tDCS demonstrates a modest but non-null effect in improving depressive symptoms. Acceptability was high as measured by discontinuation rates. tDCS is a potential novel treatment option in LLD, though large scale RCTs in LLD are required to investigate this important clinical application