Efficacy of Transcranial Direct Current Stimulation as Support for Neurorehabilitation Therapy: A Meta-analysis of Available Studies

Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive, well-tolerated, brain stimulation technique, using a weak current applied on the scalp. Rational of tDCS use has been based on the assumption of the post-stroke inter-hemispheric competition model, resulting in a hypo-excitability hemispheric lesion and a hyper-excitability healthy hemisphere, to improve the recovery of motor function. Several small studies have been published but the efficacy of tDCS is not established. We performed a systematic review of published studies to assess efficacy of tDCS on motor function of patients with stroke. A thorough search of main databases has been performed to identify randomized, controlled studies on efficacy of tDCS in patients with stroke. The values derived from the primary outcome measures of these studies have been standardized to make them comparable; eight comparisons were planned: degree of dependence, improvement of upper limb, improvement of global motor function, improvement of lower limb and visual perception; comparison between anode stimulation and sham, anode stimulation and followup. 8 studies have been included in the meta-analysis. 3 studies have been excluded because of lack of statistical data, non-randomized assignment and lack of a control group; 178 participants have been included altogether. Most of comparisons did not produce significant results; however a significant improvement of dependence scores (p=0.02), of lower limb index (p=0.02), and of visual perception (p=0.02) have been found. Despite the encouraging results by neurophysiological and instrumental investigations, in some heterogeneous cases, our study shows that there is a need to conduct studies with larger sample sizes.