Objective: To investigate changes in gait coordination quantitatively in patients with essential tremor (ET) under chronic bilateral high-frequency stimulation of the nucleus ventralis intermedius (VIM).

Background: Limb and gait ataxia following chronic VIM-DBS is a clinically relevant phenomenon, which is believed to originate from modulation of cerebello-thalamo-cortical pathways. Specific patterns of gait disturbance are also seen in patients with advanced ET (Stolze, Brain 2001; Fasano, Gait&Posture 2012), which poses the question to quantify this gait disorder to be able to differentiate between disease progression or VIM stimulation-induced gait disturbances in these patients.

Methods: Gait and balance assessment was performed in 8 patients with ET and an onset of gait disorder after VIM-DBS using an accelerometer-based kinematic motion analysis system (Mobility Lab, APDM). 5 DBS-naive patients with no subjective and objective gait disorder were measured as control group. Gait parameters were obtained from repeated 10m walks at 4 different subjective speeds. Clinical features of ataxia were assessed using SARA score.

Results: VIM-DBS patients showed an abnormal pattern of kinematic parameters and their coefficient of Variation (CoV) for 10 measures. Of the spatiotemporal measures, only gait cadence CoV and gait cycle time CoV were increased (p=.001). Range of motion (RoM) CoV of shanks and arms were higher (p<.05). Absolute RoM of trunk in sagittal, frontal and horizontal projection were increased (p<.05). Furthermore, DBS patients showed increased shank rotation asymmetry, arm symmetry index and phase coordination index (all p<.05). SARA scores did not show significant differences between groups.

Conclusions: Our findings suggest that the gait disorder associated with chronic thalamic DBS differs from gait patterns in patients with advanced ET in various parameters. It is characterized by increased asymmetry and variability not only of leg but also arm and trunk movement. The increased variability (CoV) of some spatiotemporal gait measures and increased trunk excursion are features associated with cerebellar ataxia. Cerebellar involvement via the dentate-rubro-thalamic tract has been proposed as a cause for DBS-induced ataxia. Deficits of posture and equilibrium as seen in the increased upper limb kinematics of the DBS-patients may also be explained by disturbance of midline cerebellar structures.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/quantitative-assessment-of-dbs-induced-gait-disorder-in-patients-with-essential-tremor/