Abstract
Vertical current steering (vCS) divides current between multiple contacts, which reduces radial spread to fine-tune the electric field shape and improves neuroanatomical targeting. vCS may improve the variable responsiveness of Parkinsonian gait to conventional deep brain stimulation. We hypothesized that vCS elicits greater improvement in ambulation in Parkinson’s disease patients compared to conventional, single-contact stimulation. vCS was implemented with divisions of 70%/30% and 50%/50% and compared to single-contact stimulation with four therapeutic window amplitudes in current-controlled systems. Walking at a self-selected pace was evaluated in seven levodopa-responsive patients. Integrative measures of gait and stimulation parameters were assessed with the functional ambulation performance (FAP) score and total electrical energy delivered (TEED), respectively. A two-tailed Wilcoxon matched-pairs signed rank test assessed the effect of each stimulation condition on FAP and TEED and compared regression slopes; further, a two-tailed Spearman test identified correlations. vCS significantly lowered the TEED (P < 0.0001); however, FAP scores were not different between conditions (P = 0.786). Compared to single-contact stimulation, vCS elicited higher FAP scores with lower TEED (P = 0.031). FAP and TEED were positively correlated in vCS (P = 2.000 × 10-5, r = 0.397) and single-contact stimulation (P = 0.034, r = 0.205). Therefore, vCS and single-contact stimulation improved ambulation similarly but vCS reduced the TEED and side-effects at higher amplitudes.
Highlights
Vertical current steering divides current between multiple contacts, which reduces radial spread to fine-tune the electric field shape and improves neuroanatomical targeting. vCS may improve the variable responsiveness of Parkinsonian gait to conventional deep brain stimulation
No differences in the Unified Parkinson’s Disease Rating Scale (UPDRS) motor symptom scores between vCS and single-contact stimulation across stimulation amplitudes were found, which was expected as all administered amplitudes were within the participants’
total electrical energy delivered (TEED) was minimized when vCS was employed but no differential effect was found on the functional ambulation performance (FAP) score when comparing the stimulation types (Fig. 1)
Summary
Vertical current steering (vCS) divides current between multiple contacts, which reduces radial spread to fine-tune the electric field shape and improves neuroanatomical targeting. vCS may improve the variable responsiveness of Parkinsonian gait to conventional deep brain stimulation. Deep brain stimulation (DBS) consistently relieves appendicular symptoms in Parkinson’s disease (PD) but its effect on Parkinsonian gait deficits remains more elusive and variable[1]. L-DOPA responsive gait deficits still exhibit a more variable responsiveness to STN-DBS as compared to appendicular symptoms such as tremor and rigidity. Stimulation spread into the zona incerta and/or fields of forel from STN targeted electrodes has been reported to induce gait akinesia with a paradoxical improvement of dyskinesia, rigidity, and tremor[8,9]. This outcome highlights the sensitivity of gait treatment to neuroanatomical targeting of the resultant stimulation.
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