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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. Methods: 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. Results: 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. Conclusions: 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.

ObjectivesTo investigate the effects of l‐dopa (Levodopa) and cZi‐DBS (deep brain stimulation in caudal zona incerta) on spontaneous speech intelligibility in patients with PD (Parkinson's disease).Materials and MethodsSpontaneous utterances were extracted from anechoic recordings from 11 patients with PD preoperatively (off and on l‐dopa medication) and 6 and 12 months post bilateral cZi‐DBS operation (off and on stimulation, with simultaneous l‐dopa medication). Background noise with an amplitude corresponding to a clinical setting was added to the recordings. Intelligibility was assessed through a transcription task performed by 41 listeners in a randomized and blinded procedure.ResultsA group‐level worsening in spontaneous speech intelligibility was observed on cZi stimulation compared to off 6 months postoperatively (8 adverse, 1 positive, 2 no change). Twelve months postoperatively, adverse effects of cZi‐DBS were not frequently observed (2 positive, 3 adverse, 6 no change). l‐dopa administered preoperatively as part of the evaluation for DBS operation provided the overall best treatment outcome (1 adverse, 4 positive, 6 no change).Conclusions cZi‐DBS was shown to have smaller negative effects when evaluated from spontaneous speech compared to speech effects reported previously. The previously reported reduction in word‐level intelligibility 12 months postoperatively was not transferred to spontaneous speech for most patients. Reduced intelligibility due to cZi stimulation was much more prominent 6 months postoperatively than at 12 months.

Background/Aims: Deep brain stimulation (DBS) is less effective on voice tremor than arm tremor, and it is generally assumed that successful voice tremor treatment requires bilateral DBS and possibly more precise thalamic stimulation. However, recent findings suggest that these assumptions should be reconsidered. Objectives: To evaluate whether unilateral DBS targeting the caudal zona incerta (cZi) may be sufficient to alleviate voice tremor in patients with essential tremor, or whether bilateral stimulation is needed. Methods: Seven patients with voice tremor off stimulation were evaluated during bilateral stimulation using their clinical settings, and during unilateral left stimulation in iterations with increasing stimulation amplitude. Two expert listeners assessed voice tremor severity in all samples in a blinded procedure. Results: Six patients had comparable or better effects with unilateral left stimulation compared to bilateral stimulation. For the seventh patient, unilateral DBS at a slightly higher amplitude achieved similar results as bilateral DBS. Overall, high-amplitude stimulation did not appear to be beneficial on voice tremor. Conclusions: Unilateral left and bilateral cZi-DBS had comparable effects on voice tremor in the investigated group of 7 patients. This finding suggests that the assumption that bilateral DBS is required to treat voice tremor may need to be reconsidered.

Background Deep brain stimulation of the motor thalamus or the posterior subthalamic area (PSA) shows promising results for patients with voice tremor, although only for about 50% of patients. There are indications that voice tremor requires more focused stimulation within the target area compared with hand tremor. The objective of the present study was to determine the most efficient location for reducing voice tremor within the PSA. Methods Thirty-seven patients with essential tremor were evaluated off stimulation and in a set of experimental conditions with unilateral stimulation at increasing amplitude levels. Two listeners performed blinded assessments of voice tremor from recordings of sustained vowel productions. Results Twenty-five patients (68%) had voice tremor. Unilateral stimulation reduced voice tremor for the majority of patients, and only 6 patients had poor outcomes. Contacts yielding efficient voice tremor reduction were deeper relative to the midcommissural point (MCP) and more posterior relative to the posterior tip of the subthalamic nucleus (pSTN) (z MCP = –3.1, y pSTN = –0.2) compared with poor contacts (z MCP = –0.7, y pSTN = 1.0). High-amplitude stimulation worsened voice tremor for 7 patients and induced voice tremor in 2 patients. Hand tremor improved to a greater extent than voice tremor, and improvements could be seen throughout the target area. Conclusions Our results indicate that efficient voice tremor reduction can be achieved by stimulating contacts located in the inferior part of the PSA, close or slightly posterior to the pSTN. We observed cases in which voice tremor was induced by high-amplitude stimulation.