Tremor asymmetry and the development of bilateral phase-specific deep brain stimulation for postural tremor
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Background
Tremor phase-locked deep brain stimulation (DBS) has been shown to modulate symptom severity in patients with postural tremor, including essential (ET) and dystonic tremor (DT). This, provides a potential alternative therapy that targets the underlying pathological oscillations with less energy delivered to the brain than existing systems. Previous phase-locked DBS studies focused on evaluating the effect of unilateral stimulation on the tremor-dominant hand. Considering that postural tremor usually presents bilaterally, it remains unknown how tremor asymmetry interacts with stimulation in the context of bilateral phase-locked DBS, which was investigated in the current study.
Methods
Archival limb acceleration from nine ET patients with postural tremor was analysed to explore potential asymmetries in tremor amplitude, frequency, and instability across the two upper limbs, and the relationship between these asymmetries and continuous high-frequency DBS (cDBS). Then, as a proof of concept, bilateral phase-locked DBS was tested in one ET and one DT patient with postural tremor and chronically implanted DBS devices.
Results
Our results confirmed that postural tremor is asymmetric; larger tremor power being associated with smaller amplitude and frequency stability in one hand compared to the other. These asymmetries were significantly reduced during cDBS. The effects of cDBS on aforementioned characteristics were greater on the tremor with larger amplitude. Accordingly, the effects of bilateral phasic DBS were also asymmetric.
Conclusions
This study creates a better understanding of tremor asymmetry and its relationship with DBS and provides important insights for the development of patient specific approaches for tremor.
