Noninvasive Technique May Improve Postural Balance in Parkinson Disease

Galvanic vestibular stimulation (GVS) improved measurements of postural balance in patients with Parkinson disease (PD), according to study findings published in the Journal of the Neurological Sciences.

Postural instability, difficulty with gait, and balance deficits are all aspects of PD that may lead to injuries from falls. Stimulating the brain in a non-invasive way, GVS works by directing electrical currents through electrodes placed over the mastoid processes to the vestibular system. This treatment is intended to improve postural stability and reduce falls in patients with balance disorders.

Researchers conducted a systematic review and meta-analysis, searching through 6 databases and research registers for cross-over design trials that investigated the effects of GVS on postural balance in patients with PD.

Out of 223 identified studies, they evaluated 55, selected 14 for the systematic review, and included data from 5 of the 14 in the meta-analysis. The meta-analysis combined the participants in the 5 studies for a total cohort of 40 patients with PD. 

Outcome measures that assessed postural balance included root mean square sway, sway path, sway area, sway velocity, postural angles, mean of center of pressure, and eyes closed balance tests on unstable surfaces.

While all studies directed current through the mastoid processes, some additionally accessed electrode placement over the trapezius muscle and 1 placed the anode over the C7 vertebrae. Duration of GVS treatments in these studies ranged from 26 seconds up to 3 hours.

Following statistical analysis, the researchers observed an effect size estimate of 0.43 (95% CI, 0.29-0.57; P <.001). After eliminating one outlier study, this effect size changed to 0.16 (95% CI, 0.01-0.31; P <.05).

These results suggest that GVS improved postural balance outcomes in patients with PD, and, consequently, reduced risk for falls. However, based on their analysis, the researchers could not determine the most effective type of stimulus intensity for GVS —either a fixed intensity or subject-specific noisy GVS — for modulating postural control.  

The researchers emphasized that “Our meta-analysis found GVS has a favourable effect on postural balance in PD patients, but due to limited literature and inconsistent methodologies, this favourable effect must be interpreted with caution.”

They concluded that “These findings…provide a logical basis for the use of vestibular stimulation techniques for improving postural control which may be mediated via Pedunculopontine Nucleus (PPN)-linked thalamocortical pathways that may enhance vestibular signaling in cortical circuits involved in postural control.”

Study limitations included heterogeneity of protocols and outcome measures in the included studies, small sample size, and small number of studies, indicating that these results must be interpreted with caution due to low statistical power. None of the included studies met the criteria for randomized controlled trials and only 2 of the 5 in the meta-analysis implemented double blinding.