Long-term effects of unilateral deep brain stimulation on voice tremor in patients with essential tremor

Voice tremor (VT) is a common symptom of Essential tremor (ET). Deep brain stimulation (DBS) is an established treatment for ET overall, however, its effect on VT is less clear. The aim of this study was to evaluate long-term effects of DBS on VT and to investigate how VT symptoms develop over time in patients with ET.

VT scores for the cohort of 81 ET patients that had undergone DBS surgery in the caudal zona incerta (cZi) were analyzed retrospectively. Thirty-four patients had preoperative VT and long-term evaluations were available for 19 patients. Longitudinal effects of cZi-DBS were investigated 1, 3 and 5 years postoperatively. VT progression was evaluated based on preoperative-, and off stimulation postoperative assessments.

Unilateral cZi-DBS reduced average voice tremor by 58% at the 3-year follow-up and by 67% 5 years after surgery. Four patterns of VT development were identified among patients, and the effectiveness of cZi-DBS in alleviating voice tremor symptoms showed differing patterns for these subgroups.

This retrospective analysis of a small cohort of patients suggests that cZi-DBS may reduce VT in the long-term for patients with ET overall, but the pattern of VT progression likely influences the effectiveness of the treatment. These results also suggest that unilateral cZi-DBS may be more efficacious when treating patients with mild to moderate VT. A prospective, blinded, controlled clinical trial in patients with ET is needed to determine developmental patterns of VT, and the safety and efficacy of cZi-DBS for the treatment of VT.