Objective: We sought to characterize the impact of deep brain stimulation (DBS) active contact location relative to the cerebellothalamic tract (CTT) on stimulation parameters in essential tremor (ET).

Background: DBS is an effective treatment modality for medication refractory ET [1]. Previous studies have suggested that selective activation of the CTT was associated with tremor reduction [2]. However, the longitudinal relationship between targeting the CTT and tremor reduction with DBS is not well characterized. We leveraged 7-Tesla (7T) MRI-derived tractography to precisely measure the distance between the active contact and CTT to examine whether there was a correlation between the distance of the lead from the CTT and stimulation parameters used for ET over two years.

Method: We conducted a retrospective review of 12 brain hemispheres (7 patients) in ET patients who underwent 7T MRI prior to thalamic ventral intermediate nucleus (VIM) DBS lead placement following failed medical management. 7T-derived diffusion tractography was used to locate the CTT. This image was merged with post-operative CT to calculate the distance from the active contact of the DBS lead. Clinically optimized stimulation parameters were abstracted from the chart at the time of initial programming, as well as at the 1- and 2-year follow up.

Results: Mean (SD) age was 63.9 (5.7) years with a median initial follow up time of 36.3 (13.1) days. There were 4 males, 3 females, 5 bilateral VIM DBS, and 2 Left VIM DBS implants. Mean (SD) distance to CTT was 3.1 (1.2) mm. Therapeutic current was 1.8 (1.8) mA at initial programming, 2.5 (0.6) mA at 1 year, and 2.9 (1.1) mA at the 2-year follow up. Proximity of the active contact to the CTT was associated with lower current requirements at the time of initial programming (R²=0.458, P=0.009).

Conclusion: Active DBS contact proximity to the CTT was associated with lower therapeutic current requirement shortly following DBS surgery for ET suggesting a role for activation of CTT pathways in mediating the therapeutic effect of VIM DBS for ET. While therapeutic current needs increased over time, the degree of increase was not associated with distance to the CTT. Further study is needed to examine how the relative degree of activation of the CTT pathway relates to clinical benefit of DBS for ET over time.

References: 1. Dallapiazza RF, Lee DJ, De Vloo P, et al. Outcomes from stereotactic surgery for essential tremor. J Neurol Neurosurg Psychiatry 2019; 90(4):474–482
2. Groppa S, Herzog J, Falk D, Riedel C, Deuschl G, Volkmann, J. Physiological and anatomical decomposition of subthalamic neurostimulation effects in essential tremor. Brain 2014; 137(1): 109–121.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/active-contact-proximity-to-the-ctt-predicts-initial-therapeutic-current-requirement-in-dbs-for-et-an-application-of-7t-mri/