Objective: Investigating the most effective deep brain stimulation targets to treat complex tremor cases.

Background: Deep brain stimulation (DBS) is an established treatment for medically refractory tremor sy ndromes. Ventral intermediate uncles of thalamus(Vim) is the traditional DBS target for tremor. However, due to loss of efficacy over time and stimulation induced side effects(SISE’s), other targets in the subthalamic area have been explored. Especially, stimulation of caudal zona incerta(cZI) has been found to be as effective and in some cases superior to Vim stimulation. Stimulation in cZI is also associated with SISE’s which can prove limiting for programmers to achieve most effective clinical benefit. The two nuclei -Vim and cZI are anatomically close to each other such that dual targeting with a single electrode is feasible.

Method: This case series presents medium term results of such stimulation using single 8 contact electrode in 25 patients with a range of tremor etiologies over 3 year period. A total of 47 electrodes were implanted. Trajectory planning was done using Framelink software. Post-operative CT was merged to planning MR to verify accuracy of placement. Programming team was unaware of the anatomical location of contacts. Using such technique, contacts in the subthalamic area incorporating Fields of Forel were found to offer most consistent tremor control at minimal current settings free of SISE’s.

Results: Over time 8 patients remained stable at initial settings needing only increase of current amplitude, 5 patients lost efficacy, specially around 2 year interval and others needed recruitment of additional contacts.

Conclusion: Single electrode targeting of Vim and ZI encompassing Fields of Forel in posterior subthalamic area is a safe technique and offers flexibility of a range of effective targets that can be programmed for tremor control depending on SISE’s in a given patient. Stimulation of white matter appears to be most efficacious at least at initial programming and is associated with less side effects. Long-term results are needed.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/deep-brain-stimulation-for-medically-refractory-tremor-syndromes/