Review question
To assess the effectiveness of electrical brain stimulation in improving motor and non-motor symptoms in people with idiopathic Parkinson's disease (IPD) .
Background
IPD is a neurodegenerative disorder, with the severity of the disability usually increasing with disease duration. IPD affects patients' health-related quality of life, disability, and impairment. Current rehabilitation strategies have limited effectiveness in improving these outcomes. One possibility for enhancing the effects of rehabilitation might be the addition of non-invasive electrical brain stimulation through a technique known as transcranial direct current stimulation (tDCS). This technique can alter how the brain works and may improve health-related quality of life, disability, and impairment in function in patients with IPD. However, the effectiveness of this intervention for improving rehabilitation outcomes is still unknown.
Search date
The latest search was performed on 17 February 2016.
Study characteristics
We included six trials involving 137 participants. The duration of treatment in the included trials ranged from a single session to five consecutive sessions of tDCS.
Key results
From the six trials involving 137 participants, we found there was insufficient evidence to determine how much of an effect there is from tDCS in enhancing rehabilitation outcomes regarding reduction in off time (when the symptoms are not controlled by the medication) and on time with dyskinesia (time that symptoms are controlled but the person still experiences involuntary muscle movements) , and for improving health- related quality of life, disability, and impairment in patients with IPD. However, tDCS may improve impairment regarding motor symptoms in patients with IPD. We found no study examining the effects of tDCS for improving activities of daily living. Proportions of adverse events and people discontinuing the study were comparable between groups.
Quality of evidence
All findings are based on evidence of very low quality. That means that we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
There is insufficient evidence to determine the effects of tDCS for reducing off time ( when the symptoms are not controlled by the medication) and on time with dyskinesia ( time that symptoms are controlled but the person still experiences involuntary muscle movements ) , and for improving health- related quality of life, disability, and impairment in patients with IPD. Evidence of very low quality indicates no difference in dropouts and adverse events between tDCS and control groups.
Idiopathic Parkinson's disease (IPD) is a neurodegenerative disorder, with the severity of the disability usually increasing with disease duration. IPD affects patients' health-related quality of life, disability, and impairment. Current rehabilitation approaches have limited effectiveness in improving outcomes in patients with IPD, but a possible adjunct to rehabilitation might be non-invasive brain stimulation by transcranial direct current stimulation (tDCS) to modulate cortical excitability, and hence to improve these outcomes in IPD.
To assess the effectiveness of tDCS in improving motor and non-motor symptoms in people with IPD.
We searched the following databases (until February 2016): 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. In an effort to identify further published, unpublished, and ongoing trials, we searched trial registers and reference lists, handsearched conference proceedings, and contacted authors and equipment manufacturers.
We included only randomised controlled trials (RCTs) and randomised controlled cross-over trials that compared tDCS versus control in patients with IPD for improving health-related quality of life , disability, and impairment.
Two review authors independently assessed trial quality (JM and MP) and extracted data (BE and JM). If necessary, we contacted study authors to ask for additional information. We collected information on dropouts and adverse events from the trial reports.
We included six trials with a total of 137 participants. We found two studies with 45 participants examining the effects of tDCS compared to control (sham tDCS) on our primary outcome measure, impairment, as measured by the Unified Parkinson's Disease Rating Scale (UPDRS). There was very low quality evidence for no effect of tDCS on change in global UPDRS score ( mean difference (MD) -7.10 %, 95% confidence interval (CI -19.18 to 4.97; P = 0.25, I² = 21%, random-effects model). However, there was evidence of an effect on UPDRS part III motor subsection score at the end of the intervention phase (MD -14.43%, 95% CI -24.68 to -4.18; P = 0.006, I² = 2%, random-effects model; very low quality evidence). One study with 25 participants measured the reduction in off and on time with dyskinesia, but there was no evidence of an effect (MD 0.10 hours, 95% CI -0.14 to 0.34; P = 0.41, I² = 0%, random-effects model; and MD 0.00 hours, 95% CI -0.12 to 0.12; P = 1, I² = 0%, random- effects model, respectively; very low quality evidence).
Two trials with a total of 41 participants measured gait speed using measures of timed gait at the end of the intervention phase, revealing no evidence of an effect ( standardised mean difference (SMD) 0.50, 95% CI -0.17 to 1.18; P = 0.14, I² = 11%, random-effects model; very low quality evidence). Another secondary outcome was health-related quality of life and we found one study with 25 participants reporting on the physical health and mental health aspects of health-related quality of life (MD 1.00 SF-12 score, 95% CI -5.20 to 7.20; I² = 0%, inverse variance method with random-effects model; very low quality evidence; and MD 1.60 SF-12 score, 95% CI -5.08 to 8.28; I² = 0%, inverse variance method with random-effects model; very low quality evidence, respectively). We found no study examining the effects of tDCS for improving activities of daily living. In two of six studies, dropouts , adverse events, or deaths occurring during the intervention phase were reported. There was insufficient evidence that dropouts , adverse effects, or deaths were higher with intervention (risk difference (RD) 0.04, 95% CI -0.05 to 0.12; P = 0.40, I² = 0%, random-effects model; very low quality evidence).
We found one trial with a total of 16 participants examining the effects of tDCS plus movement therapy compared to control (sham tDCS) plus movement therapy on our secondary outcome, gait speed at the end of the intervention phase, revealing no evidence of an effect (MD 0.05 m/s, 95% CI -0.15 to 0.25; inverse variance method with random-effects model; very low quality evidence). We found no evidence of an effect regarding differences in dropouts and adverse effects between intervention and control groups (RD 0.00, 95% CI -0.21 to 0.21; Mantel-Haenszel method with random-effects model; very low quality evidence).