Objective: To determine the effects of deep brain stimulation (DBS) on action tremor in Parkinson’s disease (PD) and to identify if there are specific target associations.

Background: DBS is an effective therapy for the control of PD tremor. Subthalamic nucleus (STN) and globus pallidus internus (GPi) are frequent DBS targets in PD, however there is no consensus over tremor outcomes using these targets. Although rest tremor is more prevalent in PD, action tremor, observed in 40-50% of patients, is a major contributor to functional disability.  Previous research has mostly examined the effects of DBS on rest tremor and other motor features of the disease. 

Methods: In this single-center retrospective study, we identified PD DBS patients who presented specifically with moderate-to-severe action tremor in their dominant hand. Patients were included if they scored ≥ 2 on item 21 of the Unified PD Rating Scale (UPDRS) part III. Item 20 scores (rest tremor) were noted as well. Action and rest tremor assessments were performed before surgery (off medication) and 4-6 months after surgery (off medication-on stimulation). Univariate analysis was performed using Chi square for categorical variables and Wilcoxon Mann-Whitney for non-parametric continuous variables. Comparison of baseline to postoperative outcome for each target was performed using Wilcoxon signed rank. All statistical analyses were performed in SAS 9.4. 

Results: Fifty-two patients (39 STN, 13 GPi) with significant action tremor were analyzed. The two groups were similar in age (STN 61.5 ± 10.6; GPi 66.2 ± 8.1; p = 0.4) and gender (STN 31 males; GPi 9 males; p = 0.4). Baseline mean action tremor score for STN (2.5 ± 0.7) and GPi (2.4 ± 0.5) were not statistically different (p = 0.8). With stimulation, the post-operative action tremor score decreased by an average of 1.9 points in the STN group (p <0.001) and by 1.5 points in the GPi group when compared to baseline (p < 0.001). A similar decrease was seen for mean rest tremor score (STN 1.7, p < 0.001; GPi 1.5, p < 0.001). The mean improvements in action (p = 0.3) and rest (p = 0.5) tremors were not target dependent.

Conclusions: DBS effectively controlled action PD tremor regardless of the STN vs. GPi location. Prospective studies on tremor outcomes will perform an accurate and direct comparison.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/action-tremor-control-with-deep-brain-stimulation-in-patients-with-parkinsons-disease-specific-target-associations/