Objective: To evaluate the effects of Thalamic Deep Brain Stimulation (DBS) on Gait in Orthostatic tremor (OT)

Background: OT is a rare hyperkinetic disorder of weight-bearing limbs, characterized by postural unsteadiness when standing and a high-frequency tremor of 13-18 Hz (1-2). The effects of ventral intermediate nucleus deep brain stimulation (Vim-DBS) on gait in OT patients remain unclear. 

Methods: A 74-year-old woman underwent bilateral Vim-DBS for medication-resistant OT. She received good benefit from the procedure, but the effects lessened over time. Eight years after Vim-DBS placement, a thorough gait analysis-assisted assessment of DBS settings was performed. The patient was evaluated in the following conditions: 1) DBS-OFF; 2) DBS-ON baseline (Left: contact 2-/case+, 3.9Volts, 90μsec, 185Hz; Right: contact 9-/case+, 3.9Volts, 90μsec, 185Hz); 3) DBS-ON, while evaluating different stimulation settings. Spatio-temporal gait parameters, dynamic stability index (ratio between single and double support times), and coefficient of variation of step length and swing phase were recorded and analyzed in the different conditions.

Results: After examining several parameters, a reduction of stimulation intensity (decreasing voltage by 0.3Volts and pulse width by 30μsec bilaterally) was found to be associated with objective and subjective gait improvements. The following improvements were seen in different conditions (DBS Optimized vs. DBS at Baseline vs DBS Off) respectively; Gait Velocity in cm/sec (34.93 vs 34.59 vs 33.39), Step Length in cm (49.15 vs 47.42 vs 44.87), Cadence in steps/min (85.51 vs 87.31 vs 89.52). Both DBS ON conditions also reduced the spatial and temporal variability of gait when compared to DBS-OFF. However, supra-therapeutic stimulation worsened dynamic balance in the medio-lateral and antero-posterior axes.

Conclusions: These data suggest that Vim-DBS may exert a complex and multifaceted modulation of gait in OT, most likely related to the delicate balance of two main factors: 1) an improvement of OT symptoms, which may result in increased velocity and step length; and 2) a potential induction of gait ataxia, which may result in increased stride width and time spent on double support time. This case, however, highlights the clinical utility of an integrated clinical/gait analysis approach in balancing these two opposing stimulation-related outcomes.

References:

1. Deuschl G, Bain P, Brin M. Consensus statement of the movement disorder society on tremor: Ad Hoc Scientific Committee. Mov Disord 1998; 13: 2–23.
2. Hassan A, Ahlskog JE, Matsumoto JY, et al. Orthostatic tremor: clinical, electrophysiologic, and treatment findings in 184 patients. Neurology 2016; 86: 458-464.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/gait-analysis-in-orthostatic-tremor-treated-with-thalamic-deep-brain-stimulation/