Bilateral Deep Brain Stimulation of the Ventral Intermediate Nucleus of the Thalamus Improves Objective Acoustic Measures of Essential Vocal Tremor

BACKGROUND AND OBJECTIVES: Deep brain stimulation of the ventral intermediate nucleus of the thalamus (VIM-DBS) is an established treatment for medically refractory essential tremor. However, the effect of VIM-DBS on vocal tremor remains poorly understood, with results varying by method of vocal tremor assessment and stimulation laterality. This single-center study measures the effect of bilateral VIM-DBS on essential vocal tremor using blinded objective acoustic voice analysis. METHODS: Ten patients with consecutive essential tremor with comorbid vocal tremor receiving bilateral VIM-DBS underwent voice testing before and after implantation of DBS in this prospective cohort study. Objective acoustic measures were extracted from the middle one second of steady-state phonation including cepstral peak prominence, signal-to-noise ratio, percentage voicing, tremor rate, extent of fundamental frequency modulation, and extent of intensity modulation. DBS surgery was performed awake with microelectrode recording and intraoperative testing. Postoperative voice testing was performed after stable programming. RESULTS: Patients included 6 female and 4 male, with a mean age of 67 ± 6.7 years. The VIM was targeted with the following coordinates relative to the mid-anterior commissure:posterior commissure point: 13.2 ± 0.6 mm lateral, 6.2 ± 0.7 mm posterior, and 0.0 mm below. Mean programming parameters were amplitude 1.72.0 ± 0.6 mA, pulse width 63.0 ± 12.7 µs, and rate 130.6 ± 0.0 Hz. VIM-DBS significantly improved tremor rate from 4.43 ± 0.8 Hz to 3.2 ± 0.8 Hz ( P = .001) CI (0.546, 1.895), jitter from 1 ± 0.94 to 0.53 ± 0.219 ( P = .02) CI (−0.124, 1.038), cepstral peak prominence from 13.6 ± 3.9 to 18.8 ± 2.9 ( P = .016) CI (−4.100, −0.235), signal-to-noise ratio from 15.7 ± 3.9 to 18.5 ± 3.7 ( P = .02) CI (−5.598, −0.037), and articulation rate from 0.77 ± 0.2 to 0.82 ± .14 ( P = .04) CI (−0.097, 0.008). There were no major complications in this series. CONCLUSION: Objective acoustic voice analyses suggest that bilateral VIM-DBS effectively reduces vocal tremor rate and improves voicing. Further studies using objective acoustic analyses and laryngeal imaging may help refine surgical and stimulation techniques and evaluate the effect of laterality on vocal tremor.