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Technical report
peer-reviewed

Deep Brain Stimulation for Essential Vocal Tremor: A Technical Report



Abstract

Essential vocal tremor (EVT) is the presence of a tremulous voice that is commonly associated with essential tremor. Patients with EVT often report a necessary increase in vocal effort that significantly worsens with stress and anxiety and can significantly impact quality of life despite optimal medical and behavioral treatment options. Deep brain stimulation (DBS) has been proposed as an effective therapy for vocal tremor, but very few studies exist in the literature that comprehensively evaluate the efficacy of DBS for specifically addressing EVT. We present a technical report on our multidisciplinary, comprehensive operative methodology for treatment of EVT with frameless, awake deep brain stimulation (DBS).

Introduction

Tremulous voice is a characteristic feature of several different movement disorders, including essential tremor and Parkinson’s disease, as well as other neurological diseases, such as stroke. One of the clearest associations of tremulous voice occurs in essential tremor and has been referred to as essential vocal tremor (EVT) [1]. Up to 40% of individuals diagnosed with essential tremor also present with EVT [2]. Patients with EVT often report a necessary increase in vocal effort that significantly worsens with stress and anxiety and causes significant social embarrassment. In severe cases, EVT may result in discontinuation of employment and hobbies, and thus has a significant impact on quality of life [3].

In EVT, alterations in the pitch and/or intensity of the voice are caused by rhythmic oscillations at a rate of 4-8 Hz of the laryngeal, pharyngeal and/or palatal muscles. These changes correlate with acoustic modulations of fundamental frequency (f0) for pitch and amplitude for loudness. These vocal symptoms are typically most prominent with the sustained phonation of vowels, though they are present to some degree across all phonatory activities [1, 3]. Typical oral medication-based treatments for essential tremor have not been shown to be effective at addressing vocal tremor. Botulinum toxin injected into the thyroarytenoid and extralaryngeal muscles is commonly employed for treatment of EVT and has been shown to be effective in 56-80% of patients [4]. This treatment results in a decrease in tremor amplitude; however, effects are transient, necessitating repeat injections, and a complete resolution of vocal instability is not achieved. Furthermore, these changes do not always translate into acoustic improvement or greater voice functionality. Side-effects, such as prolonged breathiness, coughing, choking and dysphagia, are the main limiting factor with botulinum injections, especially in the elderly population. [5] Thus, there clearly exists a need for a more effective, safe and permanent solution for EVT.

We present a technical report on our multidisciplinary, comprehensive operative methodology for treatment of EVT with frameless, awake deep brain stimulation (DBS).

Technical Report

Patient evaluation

Patient eligibility for DBS for EVT will be determined by a comprehensive, multi-disciplinary outpatient evaluation. Patients will have progressive, debilitating vocal tremor (and in some cases, other types of tremor, such as extremity and head tremors) that significantly interferes with daily living, and is refractory to optimal medical management with medications, such as propranolol and/or primidone [6]. In addition to neurosurgical evaluation, patients will have to be seen by both a laryngologist and a speech language pathologist for a full vocal tremor work-up. The laryngologist will perform a preoperative flexible distal-chip laryngoscopy to detail the anatomic etiology of the vocal tremor. Laryngoscopy will reveal characteristic rhythmic, oscillatory motion of the palate, pharynx, or vocal folds during a sustained phonatory vowel task [3]. The preoperative speech language pathology work-up will describe the exact acoustic and instrumental voice related characteristics of the vocal tremor in an effort to provide objective, clinically significant data about changes in voice with DBS both intra- and postoperatively.

DBS placement

The methodology and technique for awake frameless DBS has been extensively described previously [7-8], but we will detail our methodology with a specific focus on ventral intermediate nucleus (VIM) DBS targeting for vocal tremor. The location of the VIM nucleus varies by individual, but is targeted approximately 12 mm lateral to the anterior commissure - posterior commissure (AC-PC) line and 6 mm posterior to the mid-point of the AC-PC [9]. Given the medial-to-lateral facial-forelimb-hindlimb somatotopy of the thalamic motor nuclei, targets for both stimulator placements are chosen approximately 1-2 mm medial to the typical target for essential tremor in order to suppress voice tremor [10-11].

The surgery must be done in the awake state so as to ensure adequate control of vocal tremor by a speech pathologist. The large majority of patients have concomitant head and limb tremor. Thus, the awake patient is required to ensure adequate control of all or most areas of tremor, including vocal tremor. The depth of the planned medial target within VIM is calculated and entered into the microdrive with an initial depth of the microelectrode set to 15 mm above target. The microelectrode is then tested and its impedance range confirmed after conditioning. The microelectrode is then advanced in a stepwise fashion, continuously recording. Excellent single unit recordings are obtained as the electrode is advanced through the thalamus. With the aid of a neurophysiologist, kinesthetic responses encountered for the expected corresponding extremity and more proximal motor groups, neck, and face with passive range of motion, as well as with macrostimulation through the microcannula, are recorded. Macrostimulation with careful electrophysiologic documentation of paresthesias and tremor reduction/resolution is conducted as the electrode approaches the planned target trajectory. With respect to voice tremor, a speech evaluation is performed with a full intraoperative acoustic evaluation done by a speech language pathologist.

For evaluation of EVT, rate and magnitude of the f0 and amplitude modulations, which tend to co-occur, are measured and recorded [1, 12]. These measurements are the most common acoustic characteristics of vocal tremor and improvement from baseline preoperative measurements confirm adequate electrode and lead placement to specifically address vocal tremor. Additional instrumental measures of voice acoustics, including jitter, shimmer, and harmonic-to-noise ratio, and voice aerodynamics, such as maximum phonation time and s/z ratio, are also gathered to confirm improvement in both instrumental and aerodynamic measures of vocal tremor from preoperative evaluation. Elevated jitter and shimmer and decreased harmonic-to-noise ratio, s/z ratio, and maximum phonation time are typical instrumental voice findings of patients with EVT [13].

After microrecording and macrostimulation confirms adequate placement of the electrode with good vocal tremor response, the lead may be implanted along this tract. Multiple passes, while not without additional risk of morbidity [14], may be required to achieve optimal electrode placement for vocal tremor control. After appropriate attenuation of voice tremor and/or any other anatomical tremor, a Medtronic 3389 DBS stimulation electrode is measured to the appropriate length and introduced into the target point of this track. Test stimulations are done to rule out adverse effects and confirm therapeutic benefit to extremity, head, and vocal tremors. The lead position is then confirmed and secured in place.  The same procedure is repeated for the opposite side for those patients with bilateral tremor. It remains unclear if vocal tremor responds to unilateral DBS.

The patient is then brought back at a one-week interval, for infraclavicular pulse generator implantation, which is performed in standard fashion [15]. Programming of the bilateral VIM DBS are performed two weeks from implantation with both neurophysiologic and comprehensive speech analysis (see below) to confirm adequate control of vocal tremor.

Discussion

EVT is a difficult-to-treat voice disorder that significantly interferes with the quality of life of many afflicted patients despite optimal medical and behavioral treatment options [1]. DBS has been proposed as an effective therapy for vocal tremor, but very few studies exist in the literature that comprehensively evaluate the efficacy of DBS for specifically addressing EVT. Sataloff, et. al. first published on two cases of DBS specifically for the treatment of vocal tremor in 2002, in which two patients underwent bilateral stimulator implantation in the ventral intermediate nucleus (VIM) and were evaluated by strobovideolaryngoscopy and objective voice analysis. Vocal tremor was eliminated completely in one patient and significantly decreased in the other [16]. Most other published data on reduction of voice tremor following DBS have been for patients with varied pathology, and are typically not comprehensive evaluations with nasal endoscopy for direct laryngeal visualization, as well as instrumental voice assessments, including acoustics and aerodynamics [17-21]. We present a technical report detailing the methodology for comprehensive assessment of EVT prior to, during, and following frameless, awake DBS surgery. This methodology is the basis of our multidisciplinary, comprehensive DBS program for the treatment of ETV, the results of which will assist in the development of evidence-based guidelines regarding new DBS treatment paradigms for these difficult-to-serve patients.

Conclusions

Though DBS has been utilized in the treatment of vocal tremor associated with various movement disorders, very few studies specifically examine the efficacy of this treatment with comprehensive laryngoscopic and objective voice analysis. We present a technical report of our multidisciplinary, comprehensive operative methodology for treatment of EVT with frameless, awake DBS paired with a comprehensive laryngoscopic and vocal acoustic analysis to identify the optimal intraoperative stimulation targets and objectively quantify improvements in voice control. Given the encouraging results from our initial experience with this methodology, a continued prospective study of DBS for EVT is currently underway at our institution to more robustly quantify the efficacy of this treatment modality.


References

  1. Barkmeier-Kraemer J, Lato A, Wiley K: Development of a speech treatment program for a client with essential vocal tremor. Semin Speech Lang. 2011, 32:43–57. 10.1055/s-0031-1271974
  2. Wolraich D, Vasile Marchis-Crisan C, Redding N, Khella SL, Mirza N: Laryngeal tremor: Co-occurrence with other movement disorders. ORL J Otorhinolaryngol Relat Spec. 2010, 72:291–294. 10.1159/000317032
  3. Merati AL, Heman-Ackah YD, Abaza M, Altman KW, Sulica L, Belamowicz S: Common movement disorders affecting the larynx: a report from the neurolaryngology committee of the AAO-HNS. Otolaryngol Head Neck Surg. 2005, 133:654–665. 10.1016/j.otohns.2005.05.003
  4. Sulica L, Louis ED: Clinical characteristics of essential voice tremor: a study of 34 cases. Laryngoscope. 2010, 120:516–528. 10.1002/lary.20702
  5. Warrick P, Dromey C, Irish JC, Durkin L, Pakiam A, Lang A: Botulinum toxin for essential tremor of the voice with multiple anatomical sites of tremor: a crossover design study of unilateral versus bilateral injection. Laryngoscope. 2000, 110:1366–1374. 10.1097/00005537-200008000-00028
  6. Kendall KA: Vocal tremor. Mechanisms and Emerging Therapies in Tremor Disorders. GM G, Manto M (ed): Springer-Verlag New York Inc., New York, NY; 2013. 235–248.
  7. Holloway KL, Gaede SE, Starr PA, Rosenow JM, Ramakrishnan V, Henderson JM: Frameless stereotaxy using bone fiducial markers for deep brain stimulation. J Neurosurg. 2005, 103:404–413.
  8. Henderson JM, Holloway KL, Gaede SE, Rosenow JM: The application accuracy of a skull-mounted trajectory guide system for image-guided functional neurosurgery. Comput Aided Surg. 2004, 9:155–160.
  9. Papavassiliou E, Rau G, Heath S, Abosch A, Barbaro NM, Larson PS, Lamborn K, Starr PA: Thalamic deep brain stimulation for essential tremor: relation of lead location to outcome. Neurosurg. 2008, 62:884–894. 10.1227/01.NEU.0000119329.66931.9E
  10. Vitek JL, Ashe J, DeLong MR, Alexander GE: Physiologic properties and somatotopic organization of the primate motor thalamus. J Neurophysiol. 1994, 71:1498–1513.
  11. Vitek JL, Ashe J, DeLong MR, Kaneoke Y: Microstimulation of primate motor thalamus: somatotopic organization and differential distribution of evoked motor responses among subnuclei. J Neurophysiol. 1996, 75:2486–2495.
  12. Lester RA, Barkmeier-Kraemer J, Story BH: Physiologic and acoustic patterns of essential vocal tremor. J Voice. 2013, 27:422–432. 10.1016/j.jvoice.2013.01.002
  13. Gamboa J, Jimenez-Jimenez FJ, Nieto A, Cobeta I, Vegas A, Orti-Pareja M, Gasalla T, Molina JA, Garcia-Albea E: Acoustic voice analysis in patients with essential tremor. J Voice. 1998, 12:444–452. 10.1016/S0892-1997(98)80053-2
  14. Zrinzo L, Foltynie T, Limousin P, Hariz MI: Reducing hemorrhagic complications in functional neurosurgery: a large case series and systematic literature review. J Neurosurg. 2012, 116:84–94. 10.3171/2011.8.JNS101407
  15. Khan FR, Henderson JM: Deep brain stimulation surgical techniques. Handb Clin Neurol. 2013, 116:27–37.
  16. Sataloff RT, Heuer RJ, Munz M, Yoon MS, Spiegel JR: Vocal tremor reduction with deep brain stimulation: a preliminary report. J Voice. 2002, 16:132–135. 10.1016/S0892-1997(02)00082-6
  17. Carpenter MA, Pahwa R, Miyawaki KL, Wilkinson SB, Searl JP, Koller WC: Reduction in voice tremor under thalamic stimulation. Neurology. 1998, 50:796–798. 10.1212/WNL.50.3.796
  18. Taha JM, Janszen MA, Favre J: Thalamic deep brain stimulation for the treatment of head, voice, and bilateral limb tremor. J Neurosurg. 1999, 91:68–72.
  19. Groen JL, Ritz K, Contarino MF, van de Warrenburg BP, Aramideh M, Foncke EM, van Hilten JJ, Schuurman PR, Speelman JD, Koelman JH, de Bie RM, Baas F, Tijssen MA: DYT6 dystonia: Mutation screening, phenotype, and response to deep brain stimulation. Mov Disord. 2010, 25:2420–2427. 10.1002/mds.23285
  20. Moringlane JR, Putzer M, Barry WJ: Bilateral high-frequency electrical impulses to the thalamus reduce voice tremor: acoustic and electroglottographic analysis. A case report. Eur Arch Otorhinolaryngol. 2004, 261:334–336. 10.1007/s00405-003-0684-x
  21. Yoon MS, Munz M, Sataloff RT, Spiegel JR, Heuer RJ: Vocal tremor reduction with deep brain stimulation. Stereotact Funct Neurosurg. 1999, 72:241–244. 10.1159/000029732
Technical report
peer-reviewed

Deep Brain Stimulation for Essential Vocal Tremor: A Technical Report


Author Information

Allen L. Ho Corresponding Author

Department of Neurosurgery, Stanford University School of Medicine

Omar Choudhri

Department of Neurosurgery, Stanford University School of Medicine

C. Kwang Sung

Department of Otolaryngology - Head & Neck Surgery, Stanford University Medical Center

Elizabeth E. DiRenzo

Department of Otolaryngology - Head & Neck Surgery, Stanford University Medical Center

Casey H. Halpern

Department of Neurosurgery, Stanford University School of Medicine


Ethics Statement and Conflict of Interest Disclosures

Conflicts of interest: The authors have declared that no conflicts of interest exist.


Technical report
peer-reviewed

Deep Brain Stimulation for Essential Vocal Tremor: A Technical Report


Patient Reported Outcome

Patient name: Sharon Camboia

The tremors that I felt for years had become a part of me. In the beginning, as far back as my childhood, I can remember my “shakiness” being present. The reason for being shaky, however, always seemed justifiable through the years. Whether it be nervousness as a child, or a stressful day at work, as an adult there was always a valid explanation for my shaky hands. As a child, I can also remember my mother having the same symptoms that progressed into my adulthood. Again, my mother had a diagnosis of diabetes, and low blood sugar was usually the culprit of her tremors. There always seemed to be a reason for our unwelcomed shakiness. Having a reason made them seem a normal response. I had no reason to question my symptoms.

Approximately six years ago, at the age of fifty, the “normal” tremors I had been feeling all my life began to change. The nerves or stress-induced shakiness that I had grown accustomed to began to stay with me without explanation. My new symptoms had become constant, sometimes weaker, but nevertheless consistent. I woke up with shaky hands that within weeks progressed into the inability to function normally. Simple things, such as placing toothpaste on my toothbrush had become a chore. Over the next few months, the tremors that once remained in my hands had spread throughout my arms and, at times, into my legs as well. My life as I knew it was completely changed.

I quickly sought explanation through my primary physician, who first offered medication to help “control” my symptoms, often causing additional unwanted side effects. Without any positive effect I again asked for alternative treatment. I was referred to a neurologist in my home town of Merced, California. A CT scan of my brain was taken, and I never received any results. Without any new findings, I continued to search for an explanation and a cure through an additional referral to another neurologist,  Dr. Ma in Turlock, California, which led me thirty minutes out of town; an easy drive for answers. Many neurological tests were run. A repeat CT scan, MRI, blood tests to rule out multiple sclerosis and Parkinson’s disease were all conducted with “normal” findings. Negative results are supposed to be positive. However, my negative results left me without answers… and the tremors remained. Again another new medication was offered and tried with a minimal effect on my shakiness.

I began to alter my position in the business I have owned for seventeen years. I began to close myself off to the general public more and more. This tremor had found a way into every minute of my day, and affected each step in my everyday routine. I regularly turned down social appointments to avoid the feeling of embarrassment that came along with the inability to place a fork to my mouth during an afternoon lunch. My tremors had taken over, and in 2014 they had invaded my voice as well. At this point, even when I spoke, the reminder of my tremor presented itself in a tone, and vibration that made my voice sound decades older. The embarrassment that I felt just increased with my new symptom. A difficulty swallowing accompanied it as well.

At this point, multiple medications had been trialed without success, although the side effects had seemed to slow down my movement and alter my mood. I felt depressed at the idea that this would remain my life. I began to try to adjust to the idea that this was it, the tremors, and my new shaky, sometimes un-recognizable voice were here to stay. I was still determined to push for answers and I continued to ask Dr. Ma for new treatment options. She decided to refer me to Stanford Medical Center.

Once at Stanford, I was excited at the possibility of a diagnosis that would allow, at the least, a decrease in my tremors, which would allow me to regain some of my life back. My appointment was with Dr. Kilbane, neurologist. Dr. Kilbane conducted an extensive assessment of my tremors as well as my overall health. We reviewed every medication I had tried over the last 2 years. I was amazed that after two hours in her office she presented me with a diagnosis: Essential Tremor or Familial Tremor. To rule out any other diagnosis, however, Dr. Kilbane once again ordered testing and labs that again returned as normal. The Essential Tremor diagnosis was confirmed. I was impressed with the knowledge they had to offer me.

At this point, Dr. Kilbane offered one more medication for me to try. I was hesitant, but for the first time she also offered me an alternate treatment. She explained that this was the last medication we would try together. In addition, with their education and my own personal research they could offer me a surgical intervention called DBS (Deep Brain Stimulation) if this last medication was not successful. I was initially told that DBS surgery could minimize the tremors only in my hands and arms. I felt immediate relief, and a sense of hope for the first time in years. Leaving Stanford that day I finally had the answers I had searched for. Without success, our final medication trial had no effect on my tremor. Over the next six months my tremor worsened, and my voice became even more unrecognizable and hard to control. At my follow-up appointment at Stanford, I told Dr. Kilbane I was ready to move forward with the Surgical Consult.

I was confident in my experience thus far at Stanford, that DBS (Deep Brain Stimulation) could be my answer! Again, multiple tests and consultations were conducted to ensure that I was a candidate for DBS and could safely have surgery. The day that I had my surgical consult with Dr. Casey Halpern, I was impressed, to say the least. His knowledge and ability to relate to his patients was unlike my previous physicians. Dr. Casey Halpern’s bedside manner helped alleviate the concerns of my family and mine. Dr. Halpern immediately recognized my vocal tremor, and asked if that also bothered me. He asked if they could attempt to treat my vocal tremor during surgery. All of the risks and benefits of surgery were fully explained to me. I was ready. I was hopeful at the idea of a successful surgery for my hand tremors, although my voice was an added surprise that day. I was continually impressed with the staff and hopeful of a positive outcome.

Two months passed, and my surgery date was here. I was in surgery for seven hours, and awake for a great portion of it! They started with the left side of my brain, controlling the right side of my body. I could feel my tremors lesson, and I could hear the quiver in my voice decrease. Just hours out of surgery my family noted a dramatic change in my tremor, and stated that my voice sounded normal for the first time in over a year. I was told these were good results, but also known as a “honeymoon” phase. I was expected to see some return of the tremor in which my neurologists would make adjustments as needed to gain optimal results for me. Surprisingly though, months later my voice remained without tremor, although the tremors to my hand and arm returned and were able to be adjusted through stimulation. I am so grateful to Dr. Halpern, Dr. Kilbane, and all of the staff that helped me regain my life back.

Now six months later, I can truly say that DBS surgery significantly improved my life. It helped to reverse the symptoms that had taken over every aspect of my day. I can now talk to someone without having them ask me if I’m ok. I no longer have to be embarrassed when I speak or interact with people in my everyday life. The explanation every time I have a conversation is gone. I understand that this surgery comes with future adjustments and is a lifelong commitment, but it was worth it to me. I understand that my tremors are not gone, simply controlled. I am immensely thankful to Stanford Hospital and their outstanding staff for everything they have done and continue to do for me.

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Technical report
peer-reviewed

Deep Brain Stimulation for Essential Vocal Tremor: A Technical Report

  • Author Information
    Allen L. Ho Corresponding Author

    Department of Neurosurgery, Stanford University School of Medicine

    Omar Choudhri

    Department of Neurosurgery, Stanford University School of Medicine

    C. Kwang Sung

    Department of Otolaryngology - Head & Neck Surgery, Stanford University Medical Center

    Elizabeth E. DiRenzo

    Department of Otolaryngology - Head & Neck Surgery, Stanford University Medical Center

    Casey H. Halpern

    Department of Neurosurgery, Stanford University School of Medicine


    Ethics Statement and Conflict of Interest Disclosures

    Conflicts of interest: The authors have declared that no conflicts of interest exist.

    Acknowledgements


    Article Information

    Published: March 10, 2015

    DOI

    10.7759/cureus.256

    Cite this article as:

    Ho A L, Choudhri O, Sung C, et al. (March 10, 2015) Deep Brain Stimulation for Essential Vocal Tremor: A Technical Report. Cureus 7(3): e256. doi:10.7759/cureus.256

    Publication history

    Peer review began: January 13, 2015
    Peer review concluded: March 07, 2015
    Published: March 10, 2015

    Copyright

    © Copyright 2015
    Ho et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 3.0., which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

    License

    This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

Essential vocal tremor (EVT) is the presence of a tremulous voice that is commonly associated with essential tremor. Patients with EVT often report a necessary increase in vocal effort that significantly worsens with stress and anxiety and can significantly impact quality of life despite optimal medical and behavioral treatment options. Deep brain stimulation (DBS) has been proposed as an effective therapy for vocal tremor, but very few studies exist in the literature that comprehensively evaluate the efficacy of DBS for specifically addressing EVT. We present a technical report on our multidisciplinary, comprehensive operative methodology for treatment of EVT with frameless, awake deep brain stimulation (DBS).

Introduction

Tremulous voice is a characteristic feature of several different movement disorders, including essential tremor and Parkinson’s disease, as well as other neurological diseases, such as stroke. One of the clearest associations of tremulous voice occurs in essential tremor and has been referred to as essential vocal tremor (EVT) [1]. Up to 40% of individuals diagnosed with essential tremor also present with EVT [2]. Patients with EVT often report a necessary increase in vocal effort that significantly worsens with stress and anxiety and causes significant social embarrassment. In severe cases, EVT may result in discontinuation of employment and hobbies, and thus has a significant impact on quality of life [3].

In EVT, alterations in the pitch and/or intensity of the voice are caused by rhythmic oscillations at a rate of 4-8 Hz of the laryngeal, pharyngeal and/or palatal muscles. These changes correlate with acoustic modulations of fundamental frequency (f0) for pitch and amplitude for loudness. These vocal symptoms are typically most prominent with the sustained phonation of vowels, though they are present to some degree across all phonatory activities [1, 3]. Typical oral medication-based treatments for essential tremor have not been shown to be effective at addressing vocal tremor. Botulinum toxin injected into the thyroarytenoid and extralaryngeal muscles is commonly employed for treatment of EVT and has been shown to be effective in 56-80% of patients [4]. This treatment results in a decrease in tremor amplitude; however, effects are transient, necessitating repeat injections, and a complete resolution of vocal instability is not achieved. Furthermore, these changes do not always translate into acoustic improvement or greater voice functionality. Side-effects, such as prolonged breathiness, coughing, choking and dysphagia, are the main limiting factor with botulinum injections, especially in the elderly population. [5] Thus, there clearly exists a need for a more effective, safe and permanent solution for EVT.

We present a technical report on our multidisciplinary, comprehensive operative methodology for treatment of EVT with frameless, awake deep brain stimulation (DBS).

Technical Report

Patient evaluation

Patient eligibility for DBS for EVT will be determined by a comprehensive, multi-disciplinary outpatient evaluation. Patients will have progressive, debilitating vocal tremor (and in some cases, other types of tremor, such as extremity and head tremors) that significantly interferes with daily living, and is refractory to optimal medical management with medications, such as propranolol and/or primidone [6]. In addition to neurosurgical evaluation, patients will have to be seen by both a laryngologist and a speech language pathologist for a full vocal tremor work-up. The laryngologist will perform a preoperative flexible distal-chip laryngoscopy to detail the anatomic etiology of the vocal tremor. Laryngoscopy will reveal characteristic rhythmic, oscillatory motion of the palate, pharynx, or vocal folds during a sustained phonatory vowel task [3]. The preoperative speech language pathology work-up will describe the exact acoustic and instrumental voice related characteristics of the vocal tremor in an effort to provide objective, clinically significant data about changes in voice with DBS both intra- and postoperatively.

DBS placement

The methodology and technique for awake frameless DBS has been extensively described previously [7-8], but we will detail our methodology with a specific focus on ventral intermediate nucleus (VIM) DBS targeting for vocal tremor. The location of the VIM nucleus varies by individual, but is targeted approximately 12 mm lateral to the anterior commissure - posterior commissure (AC-PC) line and 6 mm posterior to the mid-point of the AC-PC [9]. Given the medial-to-lateral facial-forelimb-hindlimb somatotopy of the thalamic motor nuclei, targets for both stimulator placements are chosen approximately 1-2 mm medial to the typical target for essential tremor in order to suppress voice tremor [10-11].

The surgery must be done in the awake state so as to ensure adequate control of vocal tremor by a speech pathologist. The large majority of patients have concomitant head and limb tremor. Thus, the awake patient is required to ensure adequate control of all or most areas of tremor, including vocal tremor. The depth of the planned medial target within VIM is calculated and entered into the microdrive with an initial depth of the microelectrode set to 15 mm above target. The microelectrode is then tested and its impedance range confirmed after conditioning. The microelectrode is then advanced in a stepwise fashion, continuously recording. Excellent single unit recordings are obtained as the electrode is advanced through the thalamus. With the aid of a neurophysiologist, kinesthetic responses encountered for the expected corresponding extremity and more proximal motor groups, neck, and face with passive range of motion, as well as with macrostimulation through the microcannula, are recorded. Macrostimulation with careful electrophysiologic documentation of paresthesias and tremor reduction/resolution is conducted as the electrode approaches the planned target trajectory. With respect to voice tremor, a speech evaluation is performed with a full intraoperative acoustic evaluation done by a speech language pathologist.

For evaluation of EVT, rate and magnitude of the f0 and amplitude modulations, which tend to co-occur, are measured and recorded [1, 12]. These measurements are the most common acoustic characteristics of vocal tremor and improvement from baseline preoperative measurements confirm adequate electrode and lead placement to specifically address vocal tremor. Additional instrumental measures of voice acoustics, including jitter, shimmer, and harmonic-to-noise ratio, and voice aerodynamics, such as maximum phonation time and s/z ratio, are also gathered to confirm improvement in both instrumental and aerodynamic measures of vocal tremor from preoperative evaluation. Elevated jitter and shimmer and decreased harmonic-to-noise ratio, s/z ratio, and maximum phonation time are typical instrumental voice findings of patients with EVT [13].

After microrecording and macrostimulation confirms adequate placement of the electrode with good vocal tremor response, the lead may be implanted along this tract. Multiple passes, while not without additional risk of morbidity [14], may be required to achieve optimal electrode placement for vocal tremor control. After appropriate attenuation of voice tremor and/or any other anatomical tremor, a Medtronic 3389 DBS stimulation electrode is measured to the appropriate length and introduced into the target point of this track. Test stimulations are done to rule out adverse effects and confirm therapeutic benefit to extremity, head, and vocal tremors. The lead position is then confirmed and secured in place.  The same procedure is repeated for the opposite side for those patients with bilateral tremor. It remains unclear if vocal tremor responds to unilateral DBS.

The patient is then brought back at a one-week interval, for infraclavicular pulse generator implantation, which is performed in standard fashion [15]. Programming of the bilateral VIM DBS are performed two weeks from implantation with both neurophysiologic and comprehensive speech analysis (see below) to confirm adequate control of vocal tremor.

Discussion

EVT is a difficult-to-treat voice disorder that significantly interferes with the quality of life of many afflicted patients despite optimal medical and behavioral treatment options [1]. DBS has been proposed as an effective therapy for vocal tremor, but very few studies exist in the literature that comprehensively evaluate the efficacy of DBS for specifically addressing EVT. Sataloff, et. al. first published on two cases of DBS specifically for the treatment of vocal tremor in 2002, in which two patients underwent bilateral stimulator implantation in the ventral intermediate nucleus (VIM) and were evaluated by strobovideolaryngoscopy and objective voice analysis. Vocal tremor was eliminated completely in one patient and significantly decreased in the other [16]. Most other published data on reduction of voice tremor following DBS have been for patients with varied pathology, and are typically not comprehensive evaluations with nasal endoscopy for direct laryngeal visualization, as well as instrumental voice assessments, including acoustics and aerodynamics [17-21]. We present a technical report detailing the methodology for comprehensive assessment of EVT prior to, during, and following frameless, awake DBS surgery. This methodology is the basis of our multidisciplinary, comprehensive DBS program for the treatment of ETV, the results of which will assist in the development of evidence-based guidelines regarding new DBS treatment paradigms for these difficult-to-serve patients.

Conclusions

Though DBS has been utilized in the treatment of vocal tremor associated with various movement disorders, very few studies specifically examine the efficacy of this treatment with comprehensive laryngoscopic and objective voice analysis. We present a technical report of our multidisciplinary, comprehensive operative methodology for treatment of EVT with frameless, awake DBS paired with a comprehensive laryngoscopic and vocal acoustic analysis to identify the optimal intraoperative stimulation targets and objectively quantify improvements in voice control. Given the encouraging results from our initial experience with this methodology, a continued prospective study of DBS for EVT is currently underway at our institution to more robustly quantify the efficacy of this treatment modality.

References

  1. Barkmeier-Kraemer J, Lato A, Wiley K: Development of a speech treatment program for a client with essential vocal tremor. Semin Speech Lang. 2011, 32:43–57. 10.1055/s-0031-1271974
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Allen L. Ho, M.D., Resident Physician

Department of Neurosurgery, Stanford University School of Medicine

For correspondence:
allenlho@gmail.com

Omar Choudhri

Department of Neurosurgery, Stanford University School of Medicine

C. Kwang Sung

Department of Otolaryngology - Head & Neck Surgery, Stanford University Medical Center

Elizabeth E. DiRenzo

Department of Otolaryngology - Head & Neck Surgery, Stanford University Medical Center

Casey H. Halpern, M.D.

Department of Neurosurgery, Stanford University School of Medicine