Follow-up effects of transcranial direct current stimulation (tDCS) for the major depressive episode: A systematic review and meta-analysis.

Transcranial Direct Current Stimulation (tDCS) is an effective treatment during the acute phase of a major depressive episode (MDE), although the evidence for its follow-up efficacy is mixed. A systematic review and meta-analysis were performed. MEDLINE/PubMed, Scopus (EMBASE), Web of Science, Cochrane Library and additional sources were searched from inception to April 29, 2021. Studies that followed up adults treated with tDCS during an MDE - using (interventional) and/or not using (observational) tDCS in the follow-up period were included. The primary outcome was the Hedges' g for the follow-up depression scores. Small study effects and sources of heterogeneity were explored. 427 studies were retrieved and 11 trials (13 datasets, n = 311) were included, most presenting moderate bias. Results showed a follow-up depression improvement (k = 13, g = -0.81, 95% confidence interval [CI]: -1.28; -0.34, I² = 84.0%), which was probably driven by the interventional studies (k = 7, g= -1.12, 95% CI: -1.84; -0.40, I² = 87.1%). No predictor of response was associated with the outcome. No risk of publication bias was found. Significant between-study heterogeneity may have influenced the overall results. Our findings suggest that tDCS produces effects beyond the intervention period during MDEs. Maintenance sessions are advised in future research.