To understand the relationship between stimulation amplitude and tremor outcome in Ventral Intermediate Nucleus (VIM) Deep Brain Stimulation (DBS) in Essential Tremor (ET).

DBS response in ET may be affected by factors such as lead location, DBS stimulation parameters, and preoperative clinical characteristics.

We retrospectively reviewed the clinical outcomes of a small cohort of ET patients who underwent 7 Tesla (T) MRI brain imaging prior to undergoing VIM DBS for ET. Patients underwent stereotactic placement of DBS leads following failed medical management. Pre- and postoperative Fahn-Talosa-Marin (FTM) hemi-scores were recorded along with clinical variables (baseline disease severity, tremor history, DBS electrode settings). DBS lead location relative to the cerebellothalamic tract (CTT) was determined by 7T MRI-derived fiber tractography and post-operative CT.

The analysis included 8 brain hemispheres (6 patients, 1 female / 5 males, 2 bilateral / 3 unilateral left / 1 unilateral right implants, 7 Abbott Infinity 6172ANS leads / 1 Medtronic 3387 lead). Mean (SD) age was 60.6 years (6.5), follow-up 10 months (12), tremor history of 36.3 years (10.6), baseline FTM hemi-score 16.3 (2.9), post-operative FTM hemi-score 3.5 (2.2), stimulation amplitude 2.1mA (1.0), distance to CTT 2.7mm (1.3). Linear regression analysis showed that amplitude was negatively correlated with post-operative reduction in FTM hemi-score (P=0.006, R2=0.763). There was a trend towards lower amplitudes occurring with active electrodes that were closer to the CTT (R2=0.242), although it did not reach statistical significance.

In this patient cohort, stimulation amplitude was negatively correlated with post-operative tremor reduction. While there are several potential explanations for this observation, location of the lead near cerebellothalamic pathways could be one critical factor. We are leveraging 7T MRI-derived fiber tractography to better understand the relationship between lead location, stimulation parameters, and the relative role of fiber pathway activations to clinical outcome in VIM DBS for ET.