Background Transcranial direct current stimulation (tDCS) has shown promising clinical results, leading to increased demand for an evidence-based review on its clinical effects. Objective We convened a team of tDCS experts to conduct a systematic review of clinical trials with more than one session of stimulation testing: Pain, Parkinson’s Disease Motor Function and Cognition, Stroke Motor Function and Language, Epilepsy, Major Depressive Disorder, Obsessive-Compulsive Disorder, Tourette Syndrome, Schizophrenia and Drug Addiction. Methods Experts were asked to conduct this systematic review according to the search methodology from PRISMA guidelines. Recommendations on efficacy were categorized into: Levels A (definitely effective), B (probably effective), C (possibly effective) or no recommendation. We assessed risk of bias for all included studies to confirm whether results were driven by potentially biased studies. Results Although most of the clinical trials have been designed as proof-of-concept trials, some of the indications analyzed in this review can be considered as definitely effective (Level A) such as depression, probably effective (Level B) such as neuropathic pain, fibromyalgia, migraine, post-operative patient-controlled analgesia and pain, Parkinson´s disease (motor and cognition), stroke (motor), epilepsy, schizophrenia and alcohol addiction. Assessment of bias showed that most of the studies had low risk of biases and sensitivity analysis for bias did not change these results. Effect sizes vary from 0.01 to 0.70 and were significant in about 8 conditions, with largest effect size being in postoperative acute pain, and smaller in stroke motor recovery (nonsignificant when combined with robotic therapy). Conclusion All recommendations listed here are based on current published Pubmed-indexed data. Despite high level of evidence in some conditions, it needs to be underscored that effect sizes and duration of effects are often limited; thus, real clinical impact needs to be further determined with different study designs.

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have received compensation from Neuroelecrics Inc., manufacturers of the tested device. G. Ruffini is a shareholder of Neuroelectrics. R. Salvador, M. C. Biagi, and L. Dubreuil-Vall are employed by Neuroelectrics. A. Pascual-Leone serves on the scientific advisory boards for Starlab Neuroscience, Neuroelectrics, Magstim Inc., Nexstim, and Cognito and is listed as an inventor on several issued and pending patents on the real-time integration of transcranial magnetic stimulation with electroencephalography and MRI. A. Rotenberg is cofounder and serves on the scientific advisory board of Neuromotion. He is also presently or has recently participated on the advisory boards of Epihunter, Gamify, Neurorex, and Roche. He has had research support from Brainsway, CRE Medical, Kintai, Neuroelectrics, Roche, Sage, and Takeda. The remaining authors have no conflicts of interest to disclose. H. L. Kaye and D. San-Juan contributed equally. Funding was provided by a grant from the Massachusetts Life Sciences Center and by Neuroelectrics.

Summary: Epilepsy is a chronic disease of the brain that affects individuals of all ages and has a worldwide distribution. According to a 2006 World Health Organization report, 50 million people had epilepsy. Approximately 30% of people with epilepsy have refractory disease despite recent therapeutic developments. Consequently, new treatments are necessary. Transcranial direct current stimulation (tDCS) is a noninvasive method for cortical excitability modulation by subthreshold membrane depolarization or hyperpolarization (cathodal stimulation decreases cortical excitability, whereas anodal stimulation increases it), which has been shown to be safe, economical, and easy to use. The mechanism of action of tDCS is partially understood. Cathodal tDCS in vitro and in vivo animal studies have shown that direct current and cathodal tDCS can successfully induce suppression of epileptiform activity in EEG recordings. Cathodal tDCS has been used in heterogeneous clinical trials in pediatric and adult patients with refractory epilepsy and is well tolerated. A comprehensive review of the clinical trials based on their quality and biases shows evidence that cathodal tDCS in patients with epilepsy is potentially effective. However, additional randomized clinical trials are needed with other etiologies, special populations, additional concomitants therapies, long-term follow-up, and new parameters of stimulation.

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