Deep brain stimulation for vocal tremor: a comprehensive, multidisciplinary methodology

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.

Motor Output Variability in Movement Disorders: Insights From Essential Tremor

Findings on individuals with essential tremor suggest that tremor (within-trial movement unsteadiness) and inconsistency (trial-to-trial movement variance) stem from distinct pathologies and affect function uniquely. Nonetheless, the intricacies of inconsistency in movement disorders remain largely unexplored, as exemplified in ataxia where inconsistency below healthy levels is associated with greater pathology. We advocate for clinical assessments that quantify both tremor and inconsistency.

Voice Improvement After Essential Tremor Treatment via Focused Ultrasound and Deep Brain Stimulation

OBJECTIVES

The primary objective of this study was to determine whether two neurosurgical procedures, deep brain stimulation (DBS) and focused ultrasound (FUS), to treat essential tremor (ET) of the upper limb also reduce vocal tremor (VT) in patients with comorbid dysphonia.

METHODS

Twelve patients with ET and concomitant VT scheduled for neurosurgical intervention (FUS or DBS) or returning for follow-up after DBS implantation were assessed. FUS patients were assessed pre- and post-intervention and DBS patients were assessed with the electrodes turned on and off post-implantation. Three voice recordings of a sustained /a/ were obtained for each participant condition. Percent fundamental frequency variability (FFV) was calculated for each recorded sustained vowel. Additionally, blinded expert perceptual VT rating (VTR) was performed to assess subjective changes in tremors.

RESULTS

Of the 12 patients, seven underwent unilateral FUS, and five underwent bilateral DBS. Mean FFV without neurosurgical intervention was 18.3%, SD = 7.8 and with neurosurgical intervention was 6.3%, SD = 3.0 (t (70) =8.7, p < 0.001). Mean FFV decreased in the FUS cohort from 22.0%, SD = 7.1 pre-ablation to 6.7%, SD = 2.4 post-ablation (t (40) = 7.7, p < 0.001). Mean FFV also decreased in the DBS cohort from 15.7%, SD = 7.0 to 6.0%, SD = 3.3 when stimulation was turned on (t (28)=5.7 p < 0.001). In the FUS group, mean VTR decreased from 4.0 to 1.4 post-ablation (Z = 7.8, p < 0.001). In the DBS group, mean VTR decreased from 3.3 to 2.1 with stimulation (Z = 4.1, p < 0.001).

CONCLUSION

Neurosurgical interventions for ET (bilateral DBS and unilateral FUS) demonstrate acoustic and perceptual benefits for VT.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:367-373, 2024.

Behavioral Therapy for Tremor or Dystonia Affecting Voice in Speakers with Hyperkinetic Dysarthria: A Systematic Review

INTRODUCTION

Hyperkinetic dysarthria is characterized by atypical involuntary movements within the speech mechanism that may affect the respiratory, laryngeal, pharyngeal-oral, or velopharyngeal-nasal subsystems and may alter speech production. Although articulatory impairments are commonly considered in hyperkinetic dysarthria, speakers with hyperkinetic dysarthria may also present with changes in voice quality, pitch, and loudness. In approximately 70% of speakers with hyperkinetic dysarthria, these voice alterations are associated with tremor or dystonia. The purpose of this systematic review was to investigate the association between behavioral therapy for tremor or dystonia affecting voice in speakers with hyperkinetic dysarthria and improvement in the functional, perceptual, acoustical, aerodynamic, or endoscopic characteristics of voice.

METHOD

MEDLINE (PubMed), Embase, PsycINFO, and ClinicalTrials.gov online databases were searched in August 2017, December 2018, and April 2020 for relevant studies. The searches provided 4,921 unique records, and six additional unique records were added from other sources. Twelve studies met the criteria for inclusion in the systematic review. Participants who received concurrent medical treatment were included in this review to ensure that the search was inclusive of all relevant studies and informative for typical clinical scenarios.

RESULTS

The most commonly administered treatment ingredient was relaxation training, which was investigated in three of the four studies on tremor and three of the eight studies on dystonia. Of these six studies, only one used an experimental design and administered relaxation training as the only behavioral approach. This single-case experiment reported a significant reduction in participant ratings of tremor severity and interference with activities of daily living, although the speaking subscale reportedly did not improve and oral medications were administered concurrently. In two group studies that tested potential behavioral therapy targets, production of a low pitch improved acoustical measures for participants with essential tremor and improved auditory-perceptual judgments for participants with laryngeal dystonia. Behavioral therapy improved functional, acoustical, and aerodynamic outcomes in participants with laryngeal dystonia who were also receiving botulinum toxin injections in a randomized cross-over study and a non-randomized controlled study. Because one study employed easy onset and breathing exercises, while the other employed loud voice exercises, the mechanism of action for improvement in voice associated with behavioral therapy requires further investigation.

CONCLUSION

This systematic review describes the current evidence for treatment of tremor and dystonia affecting voice in speakers with hyperkinetic dysarthria and highlights the need for future research on behavioral therapy for these disorders.

Effect of Ventral Intermediate Nucleus Deep Brain Stimulation on Vocal Tremor in Essential Tremor

Background

There is a paucity of literature examining the effect of Ventral Intermediate Nucleus (VIM) deep brain stimulation (DBS) on voice in patients with vocal tremor (VT).

Objective

Investigate the effect of unilateral and bilateral VIM DBS on voice in patients with Essential Tremor (ET) and VT.

Methods

All patients receiving VIM DBS surgery underwent voice evaluation pre- and six-months post-operatively. We collected patient-reported quality-of-life outcome measures and acoustic voice measures of sustained phonation and connected speech. Acoustic measures specific to VT included amplitude tremor intensity index (ATRI), frequency tremor intensity index (FTRI), rate and extent of F0 modulation, and rate and extent of intensity modulation.

Results

Five patients, age 72.8 ± 2.6 years, 4 female, 1 male with mean disease duration of 29 ± 26.2 years met the inclusion criteria and were included. Two subjects had bilateral procedure and three had unilateral. We observed significant improvements in measures of vocal tremor including ATRI, FTRI, rate of F0 modulation, rate of intensity modulation, and extent of intensity modulation, as well as patient reported voice-related quality of life measured by VHI-10. Bilateral VIM DBS cases showed greater improvement in VT than unilateral cases.

Conclusion

Both unilateral and bilateral VIM DBS resulted in significant improvement of VT, with more improvement demonstrated in patients having bilateral as compared to unilateral VIM DBS. In addition, patients also reported significant improvements in voice-related quality of life. If larger studies confirm our results, VIM DBS has the potential to become a treatment specifically for disabling VT.

Optimal closed-loop deep brain stimulation using multiple independently controlled contacts

Deep brain stimulation (DBS) is a well-established treatment option for a variety of neurological disorders, including Parkinson’s disease and essential tremor. The symptoms of these disorders are known to be associated with pathological synchronous neural activity in the basal ganglia and thalamus. It is hypothesised that DBS acts to desynchronise this activity, leading to an overall reduction in symptoms. Electrodes with multiple independently controllable contacts are a recent development in DBS technology which have the potential to target one or more pathological regions with greater precision, reducing side effects and potentially increasing both the efficacy and efficiency of the treatment. The increased complexity of these systems, however, motivates the need to understand the effects of DBS when applied to multiple regions or neural populations within the brain. On the basis of a theoretical model, our paper addresses the question of how to best apply DBS to multiple neural populations to maximally desynchronise brain activity. Central to this are analytical expressions, which we derive, that predict how the symptom severity should change when stimulation is applied. Using these expressions, we construct a closed-loop DBS strategy describing how stimulation should be delivered to individual contacts using the phases and amplitudes of feedback signals. We simulate our method and compare it against two others found in the literature: coordinated reset and phase-locked stimulation. We also investigate the conditions for which our strategy is expected to yield the most benefit.

In this paper we use computer models of brain tissue to derive an optimal control algorithm for a recently developed new generation of deep brain stimulation (DBS) devices. DBS is a treatment for a variety of neurological disorders including Parkinson’s disease, essential tremor, depression and pain. There is a growing amount of evidence to suggest that delivering stimulation according to feedback from patients, or closed-loop, has the potential to improve the efficacy, efficiency and side effects of the treatment. An important recent development in DBS technology are electrodes with multiple independently controllable contacts and this paper is a theoretical study into the effects of using this new technology. On the basis of a theoretical model, we devise a closed-loop strategy and address the question of how to best apply DBS across multiple contacts to maximally desynchronise neural populations. We demonstrate using numerical simulation that, for the systems we consider, our methods are more effective than two well-known alternatives, namely phase-locked stimulation and coordinated reset. We also predict that the benefits of using multiple contacts should depend strongly on the intrinsic neuronal response. The insights from this work should lead to a better understanding of how to implement and optimise closed-loop multi-contact DBS systems which in turn should lead to more effective and efficient DBS treatments.

Proton Resonance Frequency Shift Thermometry: A Review of Modern Clinical Practices

Magnetic resonance imaging (MRI) has become a popular modality in guiding minimally invasive thermal therapies, due to its advanced, nonionizing, imaging capabilities and its ability to record changes in temperature. A variety of MR thermometry techniques have been developed over the years, and proton resonance frequency (PRF) shift thermometry is the current clinical gold standard to treat a variety of cancers. It is used extensively to guide hyperthermic thermal ablation techniques such as high-intensity focused ultrasound (HIFU) and laser-induced thermal therapy (LITT). Essential attributes of PRF shift thermometry include excellent linearity with temperature, good sensitivity, and independence from tissue type. This noninvasive temperature mapping method gives accurate quantitative measures of the temperature evolution inside biological tissues. In this review, the current status and new developments in the fields of MR-guided HIFU and LITT are presented with an emphasis on breast, prostate, bone, uterine, and brain treatments. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY STAGE: 3.

Multiparametric laryngeal assessment of the effect of thalamic deep brain stimulation on essential vocal tremor

OBJECTIVE

EVT is a refractory voice disorder that significantly affects quality of life. This work aims to conduct a multiparametric assessment of the effect of deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) on essential vocal tremor (EVT) and investigate the relation between DBS lead location and EVT outcomes.

METHODS

Nine participants underwent DBS for essential tremor and were diagnosed with co-occurring EVT in this prospective cohort study. Objective measurements including acoustic evaluation of vocal fundamental frequency (F0) and intensity modulation and subjective measurements including physiologic evaluation of the oscillatory movement of the laryngeal muscles and vocal tract and perceptual ratings of tremor severity were collected PRE and POST DBS. Finally, we investigated the relation between DBS lead location and EVT outcomes.

RESULTS

Acoustic modulations of F0 and intensity were significantly improved POST DBS. Physiologic assessment showed a POST DBS reduction of oscillatory movement in the laryngeal muscles and vocal tract, but not significantly. Listener and participant perception, of EVT severity was also significantly reduced. Finally, our results indicate better EVT control with increased distance to midline of left VIM thalamic stimulation.

CONCLUSIONS

By employing a battery of objective and subjective measures, our study supports the benefit of DBS for the treatment of EVT and specifies the acoustic and physiologic mechanisms that mediate its positive effect. We further provide preliminary results on the relation between lead location and EVT outcomes, laying the foundation for future studies to clarify the optimal DBS target for the treatment of EVT.

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.

Intraoperative Evaluation of Essential Vocal Tremor in Deep Brain Stimulation Surgery

Purpose Essential vocal tremor (EVT) is a prevalent and difficult-to-manage voice disorder. There is evidence that deep brain stimulation (DBS) of the ventral intermediate nucleus (Vim) of the thalamus may be beneficial for treating EVT. The objective of this preliminary investigation was to conduct intraoperative voice assessments during Vim-DBS implantation in order to evaluate immediate voice outcomes in medication-refractory essential tremor patients with co-occurring EVT. Method Seven adult subjects diagnosed with EVT undergoing Vim-DBS surgery participated in this investigation. Voice samples of sustained vowels were collected by a speech-language pathologist preoperatively and intraoperatively, immediately following Vim-DBS electrode placement. Voice evaluation included objective acoustic assessment of the rate and extent of EVT fundamental frequency and intensity modulation and subjective perceptual ratings of EVT severity. Results The rate of intensity modulation, extent of fundamental frequency modulation, and perceptual rating of EVT severity were significantly reduced intraoperatively as compared to preoperatively. Moderate, positive correlations were appreciated between a subset of acoustic measures and perceptual severity ratings. Conclusions The results of this study demonstrate a speech-language pathologist can conduct intra-operative evaluation of EVT during DBS surgery. Using a noninvasive, simple acoustic recording method, we were able to supplement perceptual subjective observation with objective assessment and demonstrate immediate, intraoperative improvements in EVT. The findings of this analysis inform the added value of intraoperative voice evaluation in Vim-DBS patients and contribute to the growing body of literature seeking to evaluate the efficacy of DBS as a treatment for EVT.

Objective Acoustic Quantification of Perceived Voice Tremor Severity

Purpose This study compared auditory-perceptual measures of presence/absence and severity of vocal tremor to acoustic markers of vocal tremor. The validity (both concurrent and diagnostic) of various acoustic markers of vocal tremor was also assessed. Method Fifty-six midvowel sustained [a:] recordings were selected to yield a representative convenience sample of vocal tremor. After training with 10 synthesized samples, 4 female audiologists rated these samples on "voice tremor severity" on a continuous 10-cm scale. Afterward, 15 randomly selected recordings were presented a 2nd time for intrarater reliability assessment. Customized audio signal processing in Praat yielded 12 acoustic measures of rate, extent and perturbation of fundamental frequency (f ₀), and intensity level (IL) modulation. Enter-type multiple linear regression analysis was applied to weight and combine these acoustic variables into an acoustic model of vocal tremor severity. Results After removing the vocal tremor severity ratings of 1 of the audiologists because of insufficient intra- and interrater reliability, mean single-measures consistency-type intraclass correlation coefficients equaled .83 within raters and .72 between raters. Correlation between mean ratings and the 12 acoustic markers ranged from .76 for median extent of f ₀ modulation to .11 for rate of IL modulation. Correlation between mean ratings and the acoustic model was .89. Analysis of this model's receiver operating characteristics yielded an area under receiver operating characteristic curve of .93, denoting sensitivity of .87 and specificity of .91. Conclusions This study demonstrated that auditory-perceptual ratings of vocal tremor severity are guided primarily by f ₀ and IL modulation extent, less by modulation perturbation, and least by modulation rate. The acoustic model covering all these modulation properties yielded acceptable results in terms of both concurrent and diagnostic validity. However, external cross-validation of this model is warranted before applying it in clinical voice/speech assessment.

Unilateral Thalamic Deep Brain Stimulation for Voice Tremor

BACKGROUND

Voice tremor (VT) is the involuntary and rhythmical phonatory instability of the voice. Recent findings suggest that unilateral deep brain stimulation of the ventral intermediate nucleus (Vim-DBS) can sometimes be effective for VT. In this exploratory analysis, we investigated the effect of Vim-DBS on VT and tested the hypothesis that unilateral thalamic stimulation is effective for patients with VT.

METHODS

Seven patients with VT and previously implanted bilateral Vim-DBS were enrolled in the study. Each patient was randomized and recorded performing sustained phonation during the following conditions: left thalamic stimulation, right thalamic stimulation, bilateral thalamic stimulation (Bil-ON), and no stimulation (Bil-OFF). Perceptual VT ratings and an acoustic analysis to find the rate of variation of the fundamental frequency measured by the standard deviation of the pitch (f0SD) were performed in a blinded manner. For the purposes of this study, a "dominant" side was defined as one with more than twice as much reduction in VT following Vim-DBS compared to the contralateral side. The Wilcoxon signed-rank test was performed to compare the effect of the dominant side stimulation in the reduction of VT scores and f0SD. The volume of activated tissue (VAT) of the dominant stimulation side was modelled against the degree of improvement in VT to correlate the significant stimulation cluster with thalamic anatomy. Finally, tractography analysis was performed to analyze the connectivity of the significant stimulation cluster.

RESULTS

Unilateral stimulation was beneficial in all 7 patients. Five patients clearly had a "dominant" side with either benefit only seen following stimulation of one side or more than twice as much benefit from one side compared to the other. Two patients had similar benefit with unilateral stimulation from either side. The Wilcoxon paired test showed significant differences between unilateral dominant and unilateral nondominant stimulation for VT scores (p = 0.04), between unilateral dominant and Bil-OFF (p = 0.04), and between Bil-ON and unilateral nondominant stimulation (p = 0.04). No significant differences were found between Bil-ON and unilateral dominant condition (p = 0.27), or between Bil-OFF and unilateral nondominant (p = 0.23). The dominant VAT showed that the significant voxels associated with the best VT control were located in the most ventral and medial part of the Vim nucleus and the ventralis caudalis anterior internus nucleus. The connectivity analysis showed significant connectivity with the cortical areas of the speech circuit.

CONCLUSIONS

Unilateral dominant-side thalamic stimulation and bilateral thalamic stimulation were equally effective in reducing VT. Nondominant unilateral stimulation alone did not significantly improve VT.

Deep brain stimulation in pediatric dystonia: a systematic review

While deep brain stimulation (DBS) treatment is relatively rare in children, it may have a role in dystonia to reduce motor symptoms and disability. Pediatric DBS studies are sparse and limited by small sample size, and thus, outcomes are poorly understood. Thus, we performed a systematic review of the literature including studies of DBS for pediatric (age < 21) dystonia. Patient demographics, disease causes and characteristics, motor scores, and disability scores were recorded at baseline and at last post-operative follow-up. We identified 19 studies reporting DBS outcomes in 76 children with dystonia. Age at surgery was 13.8 ± 3.9 (mean ± SD) years, and 58% of individuals were male. Post-operative follow-up duration was 2.8 ± 2.8 years. Sixty-eight percent of patients had primary dystonia (PD), of whom 56% had a pathological mutation in DYT1 (DYT1+). Across all patients, regardless of dystonia type, 43.8 ± 36% improvement was seen in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) motor (-M) scores after DBS, while 43.7 ± 31% improvement was observed in BFMDRS disability (-D) scores. Patients with PD were more likely to experience ≥ 50% improvement (56%) in BFMDRS-M scores compared to patients with secondary causes of dystonia (21%, p = 0.004). DYT1+ patients were more likely to achieve ≥ 50% improvement (65%) in BFMDRS-D than DTY1- individuals (29%, p = 0.02), although there was no difference in BFMDRS-M ≥ 50% improvement rates between DYT1+ (66%) or DYT1- (43%) children (p = 0.11). While DBS is less common in pediatric patients, individuals with severe dystonia may receive worthwhile benefit with neuromodulation treatment.

Surgical treatments for essential tremor

INTRODUCTION

Essential tremor is the most common form of pathologic tremor. Surgical therapies disrupt tremorogenic oscillation in the cerebellothalamocortical pathway and are capable of abolishing severe tremor that is refractory to available pharmacotherapies. Surgical methods are raspidly improving and are the subject of this review. Areas covered: A PubMed search on 18 January 2018 using the query essential tremor AND surgery produced 839 abstracts. 379 papers were selected for review of the methods, efficacy, safety and expense of stereotactic deep brain stimulation (DBS), stereotactic radiosurgery (SRS), focused ultrasound (FUS) ablation, and radiofrequency ablation of the cerebellothalamocortical pathway. Expert commentary: DBS and SRS, FUS and radiofrequency ablations are capable of reducing upper extremity tremor by more than 80% and are far more effective than any available drug. The main research questions at this time are: 1) the relative safety, efficacy, and expense of DBS, SRS, and FUS performed unilaterally and bilaterally; 2) the relative safety and efficacy of thalamic versus subthalamic targeting; 3) the relative safety and efficacy of atlas-based versus direct imaging tractography-based anatomical targeting; and 4) the need for intraoperative microelectrode recordings and macroelectrode stimulation in awake patients to identify the optimum anatomical target. Randomized controlled trials are needed.

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.

Cost-effectiveness of focused ultrasound, radiosurgery, and DBS for essential tremor

BACKGROUND

Essential tremor remains a very common yet medically refractory condition. A recent phase 3 study demonstrated that magnetic resonance-guided focused ultrasound thalamotomy significantly improved upper limb tremor. The objectives of this study were to assess this novel therapy's cost-effectiveness compared with existing procedural options.

METHODS

Literature searches of magnetic resonance-guided focused ultrasound thalamotomy, DBS, and stereotactic radiosurgery for essential tremor were performed. Pre- and postoperative tremor-related disability scores were collected from 32 studies involving 83 magnetic resonance-guided focused ultrasound thalamotomies, 615 DBSs, and 260 stereotactic radiosurgery cases. Utility, defined as quality of life and derived from percent change in functional disability, was calculated; Medicare reimbursement was employed as a proxy for societal cost. Medicare reimbursement rates are not established for magnetic resonance-guided focused ultrasound thalamotomy for essential tremor; therefore, reimbursements were estimated to be approximately equivalent to stereotactic radiosurgery to assess a cost threshold. A decision analysis model was constructed to examine the most cost-effective option for essential tremor, implementing meta-analytic techniques.

RESULTS

Magnetic resonance-guided focused ultrasound thalamotomy resulted in significantly higher utility scores compared with DBS (P < 0.001) or stereotactic radiosurgery (P < 0.001). Projected costs of magnetic resonance-guided focused ultrasound thalamotomy were significantly less than DBS (P < 0.001), but not significantly different from radiosurgery.

CONCLUSIONS

Magnetic resonance-guided focused ultrasound thalamotomy is cost-effective for tremor compared with DBS and stereotactic radiosurgery and more effective than both. Even if longer follow-up finds changes in effectiveness or costs, focused ultrasound thalamotomy will likely remain competitive with both alternatives. © 2017 International Parkinson and Movement Disorder Society.

The effect of unilateral thalamic deep brain stimulation on the vocal dysfunction in a patient with spasmodic dysphonia: interrogating cerebellar and pallidal neural circuits

Spasmodic dysphonia (SD) is a neurological disorder of the voice where a patient's ability to speak is compromised due to involuntary contractions of the intrinsic laryngeal muscles. Since the 1980s, SD has been treated with botulinum toxin A (BTX) injections into the throat. This therapy is limited by the delayed-onset of benefits, wearing-off effects, and repeated injections required every 3 months. In a patient with essential tremor (ET) and coincident SD, the authors set out to quantify the effects of thalamic deep brain stimulation (DBS) on vocal function while investigating the underlying motor thalamic circuitry. A 79-year-old right-handed woman with ET and coincident adductor SD was referred to our neurosurgical team. While primarily treating her limb tremor, the authors studied the effects of unilateral, thalamic DBS on vocal function using the Unified Spasmodic Dysphonia Rating Scale (USDRS) and voice-related quality of life (VRQOL). Since dystonia is increasingly being considered a multinodal network disorder, an anterior trajectory into the left thalamus was deliberately chosen such that the proximal contacts of the electrode were in the ventral oralis anterior (Voa) nucleus (pallidal outflow) and the distal contacts were in the ventral intermediate (Vim) nucleus (cerebellar outflow). In addition to assessing on/off unilateral thalamic Vim stimulation on voice, the authors experimentally assessed low-voltage unilateral Vim, Voa, or multitarget stimulation in a prospective, randomized, doubled-blinded manner. The evaluators were experienced at rating SD and were familiar with the vocal tremor of ET. A Wilcoxon signed-rank test was used to study the pre- and posttreatment effect of DBS on voice. Unilateral left thalamic Vim stimulation (DBS on) significantly improved SD vocal dysfunction compared with no stimulation (DBS off), as measured by the USDRS (p < 0.01) and VRQOL (p < 0.01). In the experimental interrogation, both low-voltage Vim (p < 0.01) and multitarget Vim + Voa (p < 0.01) stimulation were significantly superior to low-voltage Voa stimulation. For the first time, the effects of high-frequency stimulation of different neural circuits in SD have been quantified. Unexpectedly, focused Voa (pallidal outflow) stimulation was inferior to Vim (cerebellar outflow) stimulation despite the classification of SD as a dystonia. While only a single case, scattered reports exist on the positive effects of thalamic DBS on dysphonia. A Phase 1 pilot trial (DEBUSSY; clinical trial no. NCT02558634, clinicaltrials.gov) is underway at the authors' center to evaluate the safety and preliminary efficacy of DBS in SD. The authors hope that this current report stimulates neurosurgeons to investigate this new indication for DBS.

Deep Brain Stimulation Salvages a Flourishing Dental Practice: A Dentist with Essential Tremor Recounts his Experience

In recounting his experience with deep brain stimulation (DBS), a practicing dentist challenged with long-standing bilateral essential tremor of the hands shares insights into his diagnosis, treatments, and ultimately successful DBS surgery at Stanford University Medical Center, CA, USA. Now nearly one year after his surgery, his practice continues to flourish and he encourages others in his profession to consider the possibility of DBS as a definitive treatment for tremors of the hand, which may salvage their practice.

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.

A Randomized Trial of Focused Ultrasound Thalamotomy for Essential Tremor

BACKGROUND

Uncontrolled pilot studies have suggested the efficacy of focused ultrasound thalamotomy with magnetic resonance imaging (MRI) guidance for the treatment of essential tremor.

METHODS

We enrolled patients with moderate-to-severe essential tremor that had not responded to at least two trials of medical therapy and randomly assigned them in a 3:1 ratio to undergo unilateral focused ultrasound thalamotomy or a sham procedure. The Clinical Rating Scale for Tremor and the Quality of Life in Essential Tremor Questionnaire were administered at baseline and at 1, 3, 6, and 12 months. Tremor assessments were videotaped and rated by an independent group of neurologists who were unaware of the treatment assignments. The primary outcome was the between-group difference in the change from baseline to 3 months in hand tremor, rated on a 32-point scale (with higher scores indicating more severe tremor). After 3 months, patients in the sham-procedure group could cross over to active treatment (the open-label extension cohort).

RESULTS

Seventy-six patients were included in the analysis. Hand-tremor scores improved more after focused ultrasound thalamotomy (from 18.1 points at baseline to 9.6 at 3 months) than after the sham procedure (from 16.0 to 15.8 points); the between-group difference in the mean change was 8.3 points (95% confidence interval [CI], 5.9 to 10.7; P<0.001). The improvement in the thalamotomy group was maintained at 12 months (change from baseline, 7.2 points; 95% CI, 6.1 to 8.3). Secondary outcome measures assessing disability and quality of life also improved with active treatment (the blinded thalamotomy cohort)as compared with the sham procedure (P<0.001 for both comparisons). Adverse events in the thalamotomy group included gait disturbance in 36% of patients and paresthesias or numbness in 38%; these adverse events persisted at 12 months in 9% and 14% of patients, respectively.

CONCLUSIONS

MRI-guided focused ultrasound thalamotomy reduced hand tremor in patients with essential tremor. Side effects included sensory and gait disturbances. (Funded by InSightec and others; ClinicalTrials.gov number, NCT01827904.).

Deep Brain Stimulation: Expanding Applications

For over two decades, deep brain stimulation (DBS) has shown significant efficacy in treatment for refractory cases of dyskinesia, specifically in cases of Parkinson's disease and dystonia. DBS offers potential alleviation from symptoms through a well-tolerated procedure that allows personalized modulation of targeted neuroanatomical regions and related circuitries. For clinicians contending with how to provide patients with meaningful alleviation from often debilitating intractable disorders, DBSs titratability and reversibility make it an attractive treatment option for indications ranging from traumatic brain injury to progressive epileptic supra-synchrony. The expansion of our collective knowledge of pathologic brain circuitries, as well as advances in imaging capabilities, electrophysiology techniques, and material sciences have contributed to the expanding application of DBS. This review will examine the potential efficacy of DBS for neurologic and psychiatric disorders currently under clinical investigation and will summarize findings from recent animal models.