Objective: To compare the acute effects of deep brain stimulation (DBS) of unilateral subthalamic nucleus (STN) and unilateral globus pallidus interna (GPi) on motor function within individual patients who were treated for Parkinson’s disease (PD) with DBS of both unilateral targets.

Background: Individual parallel randomized controlled clinical trials indicate that DBS treatments targeting either the STN or GPi are both effective for alleviating the motor symptoms of PD. However, few studies have so far compared the motor effects of STN and GPi DBS within individual patients, which may be more relevant to actual clinical practice and patient experience.

Method: This prospective, double-blind, randomized crossover study examined 8 patients with idiopathic PD who had been treated with continuous DBS of ipsilateral STN and contralateral GPi for the duration of two years. Motor symptom severity, quantified by means of the UPDRS-III, was assessed at the time of DBS surgery and at 2-year follow-up in 4 randomized, double-blinded conditions: (1) Med-STN+GPi-, (2) Med-STN-GPi+, (3) Med+STN+GPi-, and (4) Med+STN-GPi+.

Results: The patients’ motor symptoms in both limbs were less severe in the Med- STN+GPi- condition at 2-year follow-up than seen in the Med- condition at baseline, but their axial symptoms showed substantial worsening. By contrast, bradykinesia was less severe in the Med- STN-GPi+ condition at 2-year follow-up relative to baseline, along with reduced tremor on the ipsilateral side and less severe motor symptoms in the stimulated limb. However, the patients’ axial symptoms and all subscale scores were increased in the postsurgical STN-Med-GPi+ condition.

Conclusion: Unilateral STN stimulation produced a larger improvement in most of patients’ PD motor symptoms in both the medicated and unmediated state than did unilateral GPi stimulation. However, unilateral STN stimulation also worsened gait symptoms in the med+ state, which was less severe following unilateral GPi stimulation.  Furthermore, unilateral STN stimulation acted on motor symptoms on both sides, whereas unilateral GPi stimulation mainly affected motor symptoms on the stimulated side. These results further clarify the differences in motor effects between STN DBS and GPi DBS for PD.

References: Ramirez-Zamora A, Ostrem JL. Globus Pallidus Interna or Subthalamic Nucleus Deep Brain Stimulation for Parkinson Disease: A Review. JAMA Neurol. Mar 1 2018;75(3):367-372. doi:10.1001/jamaneurol.2017.4321 Zhang C, Wang L, Hu W, et al. Combined Unilateral Subthalamic Nucleus and Contralateral Globus Pallidus Interna Deep Brain Stimulation for Treatment of Parkinson Disease: A Pilot Study of Symptom-Tailored Stimulation. Neurosurgery. May 27 2020;87(6):1139-47. doi:10.1093/neuros/nyaa201 Fasano A, Aquino CC, Krauss JK, Honey CR, Bloem BR. Axial disability and deep brain stimulation in patients with Parkinson disease. Nat Rev Neurol. Feb 2015;11(2):98-110. doi:10.1038/nrneurol.2014.252

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MDS Abstracts - https://www.mdsabstracts.org/abstract/unilateral-subthalamic-versus-unilateral-pallidal-stimulation-in-parkinsons-disease-a-randomized-double-blind-crossover-study/