Deep Brain Stimulation for Treatment of Voice Disorders

Treatment of Essential Vocal Tremor: A Scoping Review of Evidence-Based Therapeutic Modalities

OBJECTIVES/HYPOTHESIS

Essential vocal tremor (EVT) is an uncommon but challenging condition to manage. Several medical and interventional treatment options have been reported but efficacy remains unclear. We performed a scoping review of high-quality clinical trials to identify effective evidence-based treatments for EVT.

STUDY DESIGN

Scoping review.

METHODS

Relevant studies were identified using the databases MedLine, Cochrane Central Register of Controlled Trials, and Embase. Subjective and objective outcomes for each modality were analyzed and the effect sizes were quantified using Hedges' g measure to allow comparison between studies.

RESULTS

We identified 421 studies eligible for screening with 11 included in the final analysis. Evidence supporting effective EVT treatments was found for bilateral versus unilateral deep brain stimulation (DBS) (Hedges' g 0.65, 95% CI = 0.10-1.20) and octanoic acid (Hedges' g 1.15, 95% CI = 0.40-1.90). Evidence to support the use of methazolamide was not sufficient (Hedges' g 0.51, 95% CI = -0.64 to 1.66). Botulinum toxin (BT) injections were equivalent when comparing unilateral versus bilateral (Hedges' g -0.18, 95% CI = -1.06 to 0.70); BT did not display any advantage over propranolol (Hedges' g -0.47, 95% CI = -1.73 to 0.78) or injection augmentation (Hedges' g 0.068, 95% CI = -0.98 to 1.12).

CONCLUSIONS

Our review finds very little high-quality evidence supporting any treatment for EVT. Octanoic acid reduced fluctuations in EVT but did not affect the perception of the tremor. In refractory cases, bilateral DBS was superior to unilateral DBS in improving subjective voice outcomes. Unilateral and bilateral BT injections were equivalent, and BT injection was not more effective than injection augmentation. Further direct comparison in well-designed prospective studies may help clarify optimal treatment for EVT patients.

Direct subthalamic nucleus stimulation influences speech and voice quality in Parkinson's disease patients

BACKGROUND

DBS of the subthalamic nucleus (STN) considerably ameliorates cardinal motor symptoms in PD. Reported STN-DBS effects on secondary dysarthric (speech) and dysphonic symptoms (voice), as originating from vocal tract motor dysfunctions, are however inconsistent with rather deleterious outcomes based on post-surgical assessments.

OBJECTIVE

To parametrically and intra-operatively investigate the effects of deep brain stimulation (DBS) on perceptual and acoustic speech and voice quality in Parkinson's disease (PD) patients.

METHODS

We performed an assessment of instantaneous intra-operative speech and voice quality changes in PD patients (n = 38) elicited by direct STN stimulations with variations of central stimulation features (depth, laterality, and intensity), separately for each hemisphere.

RESULTS

First, perceptual assessments across several raters revealed that certain speech and voice symptoms could be improved with STN-DBS, but this seems largely restricted to right STN-DBS. Second, computer-based acoustic analyses of speech and voice features revealed that both left and right STN-DBS could improve dysarthric speech symptoms, but only right STN-DBS can considerably improve dysphonic symptoms, with left STN-DBS being restricted to only affect voice intensity features. Third, several subareas according to stimulation depth and laterality could be identified in the motoric STN proper and close to the associative STN with optimal (and partly suboptimal) stimulation outcomes. Fourth, low-to-medium stimulation intensities showed the most optimal and balanced effects compared to high intensities.

CONCLUSIONS

STN-DBS can considerably improve both speech and voice quality based on a carefully arranged stimulation regimen along central stimulation features.

Laryngeal Dystonia, Dystonic Tremor and Vocal Tremor: Three Different Entities

OBJECTIVE

The main objective of this study was to compare the demographic and clinical characteristics of patients with laryngeal dystonia (LD), dystonic tremor (DT), and vocal tremor (VT).

STUDY DESIGN

This was a retrospective longitudinal study.

METHODS

Data analysis from every patient diagnosed with LD, DT, or VT from January 1, 2010, to September 30, 2022, at a tertiary hospital center. Differential diagnosis between these entities was clinical (clinical history, voice assessment, and endoscopy) and confirmed by laryngeal electromyography.

RESULTS

A total of 87 patients were included in this study: 50 patients with LD, 23 with DT, and 14 with VT. Age at diagnosis was significantly lower in patients with LD, with a mean age of 56.2 years when compared to DT (67.6 years; P = 0.002) and VT (70.5 years; P = 0.009). Furthermore, VT had a higher female prevalence (92.9%) when compared with LD (52%; P = 0.011). LD was mainly adductor, with only two patients diagnosed with abductor LD, and DT was adductor in every case. Tremor direction in patients with VT was horizontal in 50% and mixed (horizontal + vertical) in 50%, while in DT was mixed in 65.2% and horizontal in 34.8%. LD was more commonly an isolated laryngeal movement disorder (78%) when compared to DT (47.8%; P = 0.015) or VT (28.5%; P < 0.001), which were more often secondary to generalized neurological disorders. There were no differences between groups on Voice Handicap Index-10, self-reported grade of dysphonia on a visual analogic scale (0-10), maximum phonation time, and G, R, B, A, and I in the GRBAS-I scale at diagnosis (P > 0.05). S was significantly higher in LD when compared to VT (P < 0.001) and nonsignificantly higher than in DT (P = 0.075).

CONCLUSIONS

LD, DT, and VT seem to be different entities with different demographics and clinical characteristics.

Comprehensive Evaluation of Voice-Specific Outcomes in Patients With Essential Tremor Before and After Deep Brain Stimulation

OBJECTIVE

Deep brain stimulation (DBS) is a treatment for medically refractory essential tremor (ET), but there is a paucity of literature examining the effects of DBS on voice in patients with ET pre-DBS and post-DBS. This study aimed to report a comprehensive evaluation of voice in patients with ET pre-DBS and 6-months post-DBS.

STUDY DESIGN

Case series.

METHODS

Five patients receiving DBS for ET underwent voice evaluations pre-DBS and 6-months post-DBS. One patient had concurrent ET of the vocal tract (ETVT). The evaluation included patient-reported, perceptual, acoustic, and phonatory aerodynamic analyses of voice. Voice Handicap Index-10, Grade, Roughness, Breathiness, Asthenia, Strain Scale, perturbation measures, cepstral spectral index of dysphonia, cepstral peak prominence, and mean phonatory airflow measures were also among the data collected.

RESULTS

Patients with ET presented with minimal changes in perceptual, acoustic, and phonatory aerodynamic parameters. Perceived vocal roughness significantly increased 6-months post-DBS (P = 0.047). The patient with ETVT presented with clinically significant improvement in almost all collected voice parameters 6-months post-DBS.

CONCLUSION

This is the first study to provide data encompassing auditory perceptual voice analysis, voice-specific patient-reported quality of life measures, acoustic, and phonatory aerodynamic outcomes in patients pre-DBS and 6-months post-DBS for ET. The results of our preliminary study have implications for the use of a comprehensive voice assessment to identify and measure change in voice outcomes in patients with ET and ETVT pre- and postsurgery.

Auditory-Perceptual Evaluation of Deep Brain Stimulation on Voice and Speech in Patients With Dystonia

OBJECTIVE

To determine the effects of globus pallidus interna (GPi) deep brain stimulation (DBS) on speech and voice quality of patients with primary, medically refractory dystonia.

METHODS

Voices of 14 patients aged ≥18 years (males = 7 and females = 7) with primary dystonia (DYT1 gene mutation dystonia = 4, cervical dystonia = 6, and generalized dystonia = 4) with bilateral GPi DBS were assessed. Five blinded raters (two fellowship-trained laryngologists and three speech/language pathologists) evaluated audio recordings of each patient pre- and post-DBS. Perceptual voice quality was rated using the Grade, Roughness, Breathiness, Asthenia, and Strain scale and changes in speech intelligibility were assessed with the Clinical Global Impression scale of Severity instrument. Inter-rater and intrarater reliability rates for perceptual voice ratings were assessed using the kappa coefficient.

RESULTS

Voice quality parameters showed mean improvements in Grade (P < 0.0001), Roughness (P = 0.0043), and Strain (P < 0.0001) 12 months post-DBS. Asthenia increased from baseline to 6 months (P = 0.0022) and declined significantly from 6 to 12 months (P = 0.0170). Breathiness did not change significantly over time. Speech intelligibility also improved from 6 to 12 months (P = 0.0202) and from pre-DBS to 12 months post-DBS (P = 0.0022). Grade and Strain ratings had nearly perfect and substantial inter-rater agreement (0.84 and 0.71, respectively).

CONCLUSIONS

Voice and speech intelligibility improved after bilateral GPi DBS for dystonia. GPi DBS may emerge as a potential treatment option for patients with medically refractory laryngeal dystonia.

Voice Tremor Outcomes of Subthalamic Nucleus and Zona Incerta Deep Brain Stimulation in Patients With Parkinson Disease

OBJECTIVES

We aimed to study the effect of deep brain stimulation (DBS) in the subthalamic nucleus (STN) and caudal zona incerta (cZi) on level of perceived voice tremor in patients with Parkinson disease (PD).

STUDY DESIGN

This is a prospective nonrandomized design with consecutive patients.

METHODS

Perceived voice tremor was assessed in patients with PD having received either STN-DBS (8 patients, 5 bilateral and 3 unilateral, aged 43.1-73.6 years; median = 61.2 years) or cZi-DBS (14 bilateral patients, aged 39.0-71.9 years; median = 56.6 years) 12 months before the assessment. Sustained vowels that were produced OFF and ON stimulation (with simultaneous l-DOPA medication) were assessed perceptually in terms of voice tremor by two raters on a four-point rating scale. The assessments were repeated five times per sample and rated in a blinded and randomized procedure.

RESULTS

Three out of the 22 patients (13%) were concluded to have voice tremor OFF stimulation. Patients with PD with STN-DBS showed mild levels of perceived voice tremor OFF stimulation and a group level improvement. Patients with moderate/severe perceived voice tremor and cZi-DBS showed marked improvements, but there was no overall group effect. Six patients with cZi-DBS showed small increases in perceived voice tremor severity.

CONCLUSIONS

STN-DBS decreased perceived voice tremor on a group level. cZi-DBS decreased perceived voice tremor in patients with PD with moderate to severe preoperative levels of the symptom.

Thalamic Deep Brain Stimulation for Essential Tremor Also Reduces Voice Tremor

OBJECTIVE

Voice tremor is a common feature of essential tremor (ET) that is difficult to treat medically and significantly affects quality of life. Deep brain stimulation (DBS) of the ventral intermediate nucleus (Vim) of the thalamus is effective in improving contralateral distal limb tremor and has been shown in limited studies to affect voice tremor. Our objective was to retrospectively evaluate whether Vim-DBS used to treat patients with essential motor tremor also effectively treated underlying concurrent voice tremor and assess whether particular lead locations were favorable for treating vocal tremor.

MATERIALS AND METHODS

In this retrospective cohort study, patients had unilateral or bilateral lead placement and were monitored for up to 12 months. We used the Fahn-Tolosa-Marin (FTM) subscore to assess vocal tremor. Changes in vocal tremor before and after stimulation and over several sessions were assessed.

RESULTS

Of the 77 patients who met the inclusion criteria and were treated for essential tremor, 20 (26%) patients had vocal tremor prior to stimulation. Active Vim-DBS decreased the amplitude of voice tremor by 80% (p < 0.001). The mean FTM score as 1.24 pre-operation, 1.08 post-implantation (consistent with a lesion effect), and 0.25 with stimulation. The effect magnitude was maintained at last follow-up with slight improvement over time (p < 0.05). Unilateral and bilateral stimulation resulted in similar degrees of tremor reduction. A model of the centroid of stimulation showed that Vim thalamic stimulation that is more anterior on average yielded better voice tremor control, significantly so on the left side (p < 0.05). Additionally, there was improvement in head, tongue, and face tremor scores (p < 0.05).

CONCLUSIONS

Unilateral and bilateral Vim-DBS targeted to treat the motor component of essential tremor also dramatically decreased the amplitude of voice tremor in this group of patients, suggesting a potential benefit of this treatment for affected patients.

Vocal Tremor: Novel Therapeutic Target for Deep Brain Stimulation

Tremulous voice is characteristically associated with essential tremor, and is referred to as essential vocal tremor (EVT). Current estimates suggest that up to 40% of individuals diagnosed with essential tremor also present with EVT, which is associated with an impaired quality of life. Traditional EVT treatments have demonstrated limited success in long-term management of symptoms. However, voice tremor has been noted to decrease in patients receiving deep brain stimulation (DBS) with the targeting of thalamic nuclei. In this study, we describe our multidisciplinary procedure for awake, frameless DBS with optimal stimulation targets as well as acoustic analysis and laryngoscopic assessment to quantify tremor reduction. Finally, we investigate the most recent clinical evidence regarding the procedure.