Effects of non-invasive brain stimulation on freezing of gait in parkinsonism: A systematic review with meta-analysis

Introduction: To investigate the effect of non-invasive brain stimulation (NIBS), including repetitive transcranial magnetic stimulation and transcranial direct current stimulation, on freezing of gait (FOG) in parkinsonism. Methods: The PubMed, EMBASE, Cochrane Central Register of Controlled Trials, and Physiotherapy Evidence Database (PEDro) databases were searched up to October 2018 for articles published in English or Korean. Quality assessment was performed using the PEDro scale. Studies with random allocation and pre-intervention and post-intervention assessments for FOG were included, and the standardized mean differences for each outcome were calculated. Results: Seven studies including 102 participants were included in the final analysis. The meta-analysis showed a significant improvement in freezing of gait questionnaire (FOG-Q) scores (SMD = 0.28; 95% CI, 0.01 to 0.55) and turning time (SMD = 0.30; 95% CI, 0.02 to 0.58). When analyzing only participants with Parkinson's disease, the effect size according to the FOG-Q score was greater (SMD = 0.57; 95% CI, 0.15 to 0.98) and the United Parkinson's disease rating scale-III score was significantly improved after NIBS (SMD = 0.43; 95% CI, 0.01 to 0.86). Both motor and frontal cortex stimulation didn't reveal significant improvement for FOG, but, the effect size of motor cortex stimulation (SMD = 0.35; 95% CI, −0.06 to 0.76) was almost double compared with that of frontal cortex stimulation (SMD = 0.19; 95% CI, −0.26 to 0.63). Conclusion: NIBS showed a beneficial effect on FOG in parkinsonism, and the effects were more prominent in Parkinson's disease. Further studies are needed to determine the optimal protocol and elucidate effects according to the intervention and disease type.