To determine the effect of ventral intermediate thalamic nucleus (VIM) deep brain stimulation (DBS) on gait parameters in patients with essential tremor (ET).

DBS is an established treatment for medication-refractory ET. ET can be associated with primary gait impairment; additionally, the effect of VIM-DBS on gait is currently debated, with reports ranging from a more frequently observed worsening to an improvement with therapeutic stimulation. Determining VIM-DBS effects on gait is pivotal to determine patient candidacy for this treatment.

Database review from our kinematics laboratory identified 27 patients (women, 15; men, 12) with ET who underwent VIM-DBS (bilateral, 5; unilateral, 22) and pre- and post-DBS quantitative gait kinematics analysis with a 3D commercial motion analysis (MA) system. Post-DBS assessments were performed on stimulation. Changes in gait outcomes from pre- to post- were expressed as effect sizes (Cohen’s d) and categorized as “small,” “medium,” or “large” using established cutoff values. Post-DBS Tremor Research Group Essential Tremor Rating Scale motor scores on and off stimulation were retrospectively reviewed and available for 22 patients; percent change of on versus off stimulation was calculated and scores were compared with paired samples t-tests.

Patients underwent DBS at a mean age of 69.4±8.5 years (Table 1). The average percent reduction of the contralateral upper limb tremor scores on versus off stimulation was 80.4±13.2 (p<0.001), 9.7±3.3 months after surgery. Postoperative MA was performed 9.2±3.2 months after surgery. Small worsening effects were observed in gait speed (d=-0.32), cadence (d=-0.39), and step length (d=-0.24), which were not statistically significant (Figure 4). No changes were observed in step width.

Thalamic DBS improved tremor scores, but we observed a small, non-statistically significant, worsening trend of some gait parameters. Further study is required to clarify the observed effect of VIM-DBS on gait and identify pre-DBS gait features predictive of poor gait outcomes.