The effects of transcranial direct current stimulation (tDCS) on clinical symptoms in schizophrenia: A systematic review and meta-analysis

Objective: This systematic review and meta-analysis aims to examine the effects of transcranial direct current stimulation (tDCS) on clinical symptoms in schizophrenia. Methods: A literature search was performed for articles published in English using the following databases: MEDLINE, EMBASE, PsycINFO, INSPEC, the Cumulative Index to Nursing & Allied Health Literature Plus (CINAHL Plus), AMED, Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, EU Clinical Trials Register, and WHO International Clinical Trials Registry Platform, from their inception to October 2019. The primary outcome variables were the clinical symptoms of schizophrenia including positive symptoms, negative symptoms, and auditory hallucinations. Results: 16 randomized controlled trials (RCTs) were included in the meta-analysis, with a sample of 326 patients with active and with 310 sham tDCS. Active tDCS was found to be more effective in improving positive symptoms [standardized mean difference (SMD) = 0.17; 95 % confidence interval (CI) 0.001 to 0.33], negative symptoms [SMD = 0.43, 95 % CI 0.11, 0.75] and auditory hallucinations [SMD = 0.36 95 % CI 0.02, 0.70]. Subgroup analyses showed better results in cases of pure diagnosis of schizophrenia, higher frequency and more sessions of stimulation. Conclusion: tDCS was effective in improving positive symptoms, negative symptoms and auditory hallucination in schizophrenia. It therefore has potential as a safe and well-tolerated adjunctive intervention for schizophrenia.