The Impact of Deep Brain Stimulation Target Site on Kinematic Postural Stability Outcomes in Patients with Parkinson’s Disease

Introduction: Deep brain stimulation (DBS) targeting the subthalamic nucleus (STN) or globus pallidus internus (GPi) improves the motor symptoms of Parkinson’s Disease (PD), however the effect of DBS target on postural instability (PI) remains unclear. PI is evaluated with the pull test and scored on the Unified Parkinson’s Disease Rating Scale. Our previous work has shown that PI can be quantitatively assessed by varying the pull test intensity while the patient undergoes multiple pulls with inertial monitoring units. Kinematic variables such as increased step length (SL) and peak center of mass velocity (PCOMV) after a pull may indicate improvements in PI outcomes. Our objective is to use SL and PCOMV to determine if STN-DBS and GPi-DBS yield different PI outcomes one year post-implantation.

Methods: Thirty-three patients (9 with STN-DBS and 24 with GPi-DBS) were evaluated. Linear mixed models for SL and PCOMV were generated using intervention (medication state, DBS target and state) as the predictor, adjusting for pull intensity (peak center of mass acceleration during the pull). The models were bootstrapped for 1000 iterations, yielding estimated marginal means (emmean) and contrasts between interventions. The primary contrast of interest was between patients on medications with GPi-DBS (ON-MED-ON-GPi) versus STN-DBS (ON-MED-ON-STN) at one-year follow-up.

Results: SL for patients ON-MED-ON-GPi was 26.9 (1.6) cm, and 31.4 (2.7) cm for those ON-MED-ON-STN, demonstrating no significant difference (p>0.05). PCOMV for patients ON-MED-ON-GPi was 94.9 (4.6) cm/s, and 117.4 (7.4) cm/s for ON-MED-ON-STN, demonstrating no significant difference (p>0.05).

Conclusion : Our preliminary results indicate that there may not be significant differences between STN-DBS and GPi-DBS in terms of PI outcomes. Thus, other factors associated with GPi-DBS or STN-DBS may need to be prioritized to determine the most effective stimulation target to improve outcomes in patients with PD.