Transcranial direct current stimulation for improving idiopathic Parkinson's syndrome. An abridged version of a Cochrane review

INTRODUCTION: Idiopathic Parkinson's Disease (IPD) is a neurodegenerative disorder. The severity of disability usually increases with disease duration and affects patients' impairment, disability and health-related quality of life. A possible adjunct to improve outcomes in patients with IPD might be transcranial direct current stimulation (tDCS) to modulate cortical excitability and hence improving outcomes in people with IPD. EVIDENCE ACQUISITION: Until February 2016 we searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL; the Cochrane Library; 2016, Issue 2), MEDLINE, EMBASE, CINAHL, AMED, Science Citation Index, the Physiotherapy Evidence Database (PEDro), Rehabdata, and Inspec and handsearched conference proceedings, and contacted authors and equipment manufacturers. We included only randomized controlled trials (RCTs) and randomized controlled crossover trials comparing tDCS versus control interventions in adults with IPD. EVIDENCE SYNTHESIS: Two authors independently extracted data and assessed trial quality. We included six trials with 137 participants. There was no effect of tDCS compared to sham tDCS in our primary outcome measure, impairment, as measured by the proportional change of the Unified Parkinson's Disease Rating Scale (UPDRS) (mean difference (MD) -7.10%, 95% confidence interval (CI) -19.18 to 4.97; P=0.25). There was evidence of an effect on UPDRS part III motor subsection score at the end of the intervention period (MD -14.43%, 95% CI -24.68 to -4.18; P=0.006). There was no evidence of an effect regarding the reduction in off time and on time with dyskinesia (MD 0.10 hours, 95% CI -0.14 to 0.34; P=0.41; and MD 0.00 hours, 95% CI -0.12 to 0.12; P=1, respectively). There was no evidence of an effect for gait speed, health related quality of life and safety/acceptability, measured by dropouts and adverse events (including death). CONCLUSIONS: There is insufficient evidence to determine the effects of tDCS in reducing off time and on time with dyskinesia and for improving health-related quality of life, disability and impairment in patients with IPD.