Exploring Non-invasive Brain Stimulation Effects on Physical Outcomes in People With Parkinson’s Disease: An Umbrella Evidence Mapping Review With Meta-analyses

Background. Non-invasive brain stimulation (NIBS) is sometimes used alongside medication to alleviate motor symptoms in people with Parkinson’s disease (PD). However, the evidence supporting NIBS’s effectiveness for improving motor function in PD patients is uncertain. Objective. This umbrella review aims to synthesize recent systematic reviews and meta-analyses that have evaluated the effectiveness of NIBS in improving motor function in people with PD, with a key focus being to examine the quality of the evidence presented. Methods. The review protocol was registered in PROSPERO (CRD42022380544) and conducted per Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The search strategy was guided by the Population, Intervention, Comparison, and Outcome framework, focusing on individuals with idiopathic PD (Hoehn and Yahr stages 1-4). The review included studies comparing various NIBS techniques (eg, repetitive transcranial magnetic stimulation and transcranial direct current stimulation) to sham or alternative treatments, targeting motor and cognitive regions. Six databases were searched up to June 2024. Methodological quality was assessed using Assessment of Multiple Systematic Reviews 2 (AMSTAR2), and random-effects meta-analyses were performed to pool standardized mean differences (SMDs). Results. The final analysis included 31 meta-analyses and 10 systematic reviews. Overall, the reviews were rated as moderate quality (54% average for AMSTAR2). NIBS showed a small-to-moderate effect on motor function (Unified Parkinson’s Disease Rating Scale-Section III scores; SMD = −0.80), functional mobility (gait speed and timed-up-and-go; SMD = −0.39), and freezing of gait (SMD = −0.58), but no significant effect on balance. Conclusion. NIBS offers small-to-moderate benefits for motor symptoms and functional movement in PD, though it does not significantly impact balance. Practitioners should consider the variety of techniques and treatment parameters before application.