Effect of lead trajectory on the response of essential head tremor to deep brain stimulation.

Background: Essential tremor (ET) is one of the most common movement disorders. Normally ET affects the distal upper extremities, but it can also be accompanied by midline symptoms. Ventralis intermedius (VIM) thalamic deep brain stimulation (DBS) has been shown to be effective in reducing hand tremor, but its effects on head tremor have been inconsistent.

Methods: Twenty-nine DBS patients with a diagnosis of ET met inclusion criteria. All implantations targeted VIM. The factors examined included age, gender, disease duration, presence or absence of head tremor, handedness, and the Fahn-Tolosa-Marin rating scale (TRS). This analysis specifically focused on TRS head tremor sub-scores at baseline, 6 months and 12 months post-DBS. Additionally, DBS lead entry angles were examined.

Results: Twenty-three ET patients underwent unilateral DBS and six underwent staged bilateral DBS. At both 6 and 12 months following DBS, stimulation resulted in diminished head tremor (ON vs OFF; p < 0.0001). The most important predictor of head tremor suppression was the entry angle of the DBS lead in the sagittal projection relative to the AC-PC axial plane (AC-PC angle). Head tremor reduction was greater among more vertical AC-PC angles.

Conclusion: A more vertical AC-PC angle of the DBS lead trajectory was associated with improved head tremor suppression. Further studies will be necessary to confirm this potentially important finding.