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Impact of deep brain stimulation in the caudal zona incerta on voice tremor and speech in persons with essential tremor
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Speech and Language Therapy. (Linda Sandström)ORCID iD: 0000-0002-7626-2889
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Objectives: Deep brain stimulation (DBS) is a symptomatic treatment for people with essential tremor (ET) who have unsatisfactory tremor relief with pharmacological treatment alone. A common symptom of ET is voice tremor, but only about 50% of patients with voice tremor get a satisfactory result with DBS. Moreover, stimulation-induced adverse effects on speech are often reported, especially with bilateral stimulation. In recent years, the caudal zona incerta (cZi) has been highlighted as a particularly efficient DBS-target for tremor; however, less is known about the effects of cZi-DBS on voice and speech. The aims of this thesis were to (i) describe how voice tremor and speech production are affected by habitual cZi-DBS optimized to treat the motor symptoms of ET, (ii) investigate how voice tremor and speech production are affected by unilateral cZi-stimulation at increasing amplitudes, with a particular focus on high-amplitude stimulation, and (iii) explore the extent to which patient characteristics and DBS related factors, such as electrode location and stimulation settings, influence the outcome.

Methods: This thesis comprises two different study protocols. Study I was a retrospective study of 19 patients with ET and voice tremor, and DBS effects on voice tremor were evaluated from clinical assessments made at baseline and 1, 3, and 5 years after surgery, respectively. Studies II-V included 37 persons with ET, and DBS effects on voice tremor and speech production were evaluated off- and on habitual stimulation, as well as in an experimental protocol with unilateral stimulation at increasing amplitudes (up to a maximum of 4.5V). Voice tremor (study II, III) was assessed by two listeners using the Visual Sort and Rate (VISOR) method. Speech intelligibility (study IV) was estimated from orthographic transcriptions of nonsense sentences made by two speech-language pathology students. Speech function, including articulation and voice quality (study V) were analysed in 14 participants and assessed by two speech-language pathologists using VISOR. Voice and speech outcomes following the experimental stimulation condition were evaluated in relation to the location of the active electrode contacts.

Results: Habitual cZi-DBS reduced voice tremor at all examinations and did not affect speech production on the group-level. By contrast, during unilateral high-amplitude stimulation, more negative effects on speech were noted, and the proportion of individuals with affected speech more than doubled at maximal amplitude stimulation compared with habitual cZi-DBS (40% compared to 17%). While most of these adverse effects were mild in general, a few participants exhibited more severe impairments of high-amplitude stimulation, especially on speech intelligibility and articulation. There were also cases in which high-amplitude stimulation worsened voice tremor or even induced the symptom. As for the contribution of electrode location, a deeper and more posterior stimulation origin were found to yield the most efficient voice tremor reduction, more medially located electrodes were associated with affected articulation, whereas deteriorated speech intelligibility was related to stimulation originating from a more superior location.

Conclusions: cZi-DBS is relatively safe in the sense that adverse effects on speech production are rarely seen during stimulation with the clinical settings. Furthermore, voice tremor can be expected to improve, both short- and long- term, although not always to such an extent that the symptom is alleviated completely. However, by increasing the stimulation amplitude beyond the clinical setting, one increases the risk of inducing unwanted speech-related effects and worsen voice tremor. Thus, it appears as though the challenge in the postoperative management of the DBS treatment lies in maintaining the therapeutic effect while still keeping the stimulation amplitude at a low level. The combined results of this thesis indicate that the best outcome for voice and speech might be achieved by stimulating from the posterior-inferior-lateral part of the cZi.

Abstract [sv]

Essentiell tremor är en vanlig rörelsestörningssjukdom som kännetecknas av tremor (skakningar) främst i armar och händer, men det är även vanligt att rösten drabbas. Djup hjärnstimulering (deep brain stimulation, DBS) är en kirurgisk behandlingsmetod som visats vara mycket effektiv på tremor överlag, dock är resultaten gällande rösttremor mer varierande. Dessutom är talpåverkan en vanlig bieffekt av DBS, speciellt vid bilateral stimulering. I denna avhandling har DBS i kaudala zona incerta (cZi) utvärderats gällande dess effekter på rösttremor och talproduktion hos personer med ET. Syftet med avhandlingen är att: (i) beskriva effekterna av kronisk cZi-DBS som optimerats för att behandla ET, (ii) utforska effekterna av unilateral stimulering vid successivt ökande amplituder (med ett särskilt fokus på högamplitudstimulering), samt (iii) undersöka vilka faktorer som kan tänkas påverka resultatet.

Delstudie 1 är en retrospektiv långtidsstudie av 19 patenter med ET som hade rösttremor innan DBS-behandling. Effekterna av DBS på rösttremor utvärderades från bedömningar gjorda vid uppföljningar 1, 3 samt 5 år efter operation. Delstudie 2-5 inkluderade 37 personer med ET och effekterna av DBS på rösttremor och talproduktion utvärderades utifrån bedömningar gjorda: 1) med DBS avstängd, 2) med kronisk cZi-DBS, samt 3) vid unilateral stimulering i en experimentell procedur med gradvis ökande amplituder (upp till maximalt 4.5V). Rösttremor (delstudie 2 och 3) bedömdes perceptuellt av två lyssnare. Talförståelighet (delstudie 4) beräknades som procent korrekt uppfattade ord utifrån ortografiska transkriptioner av nonsensmeningar som utfördes av två logopedstudenter. Talfunktion, inklusive artikulation och röstkvalitet hos 14 personer med ET (delstudie 5) bedömdes perceptuellt av två erfarna logopeder. Röst- och talresultat från den experimentella stimuleringsproceduren utvärderades också i förhållande till elektrodens anatomiska läge.

Resultaten visade att kronisk cZi-DBS inte hade några negativa effekter på talproduktion överlag. Kronisk cZi-DBS förbättrade också rösttremor genomgående, dock med en betydande individuell variation. Under unilateral högamplitudsstimulering visade sig däremot fler negativa effekter på såväl rösttremor som på talproduktion. Vid stimulering med den maximala amplitudnivån hade andelen individer med talpåverkan mer än fördubblats jämfört med den vid kronisk cZi-DBS (från 17 % till 40 %). Även om dessa negativa effekter var små generellt sett var det tydligt att enskilda individers tal drabbades mer än andras. Vad gäller betydelsen av elektrodens läge inom cZi visade det sig att ett djupare och mer posteriort läge var gynnsamt för rösttremor. För talproduktion var negativa effekter förknippade med ett mer medialt läge (för artikulation) samt ett högre läge (för talförståelighet).

Sammantaget tyder avhandlingens resultat på att cZi-DBS sällan orsakar negativa effekter på tal när patienten stimuleras med de kliniska inställningarna (optimerade för att behandla symptomen av ET). Dessutom kan rösttremor förväntas förbättras, både på kort och på lång sikt. Däremot kan talpåverkan och negativa effekter på rösttremor framkallas om stimuleringsamplituden höjs. Utmaningen i den postoperativa behandlingen ligger således i att kunna bibehålla den terapeutiska behandlingseffekten samtidigt som stimuleringsamplituden hålls ner. Våra resultat antyder också att det kan vara bäst för patienters röst och tal om stimuleringen utgår från ett djupare, mer posteriort och mindre medialt läge inom cZi-området.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2020. , p. 67
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 2068
Keywords [en]
caudal zona incerta, deep brain stimulation, essential tremor, speech function, speech intelligibility, speech production, voice tremor
National Category
Other Medical Sciences not elsewhere specified Neurosciences
Identifiers
URN: urn:nbn:se:umu:diva-166784ISBN: 978-91-7855-163-7 (electronic)ISBN: 978-91-7855-162-0 (print)OAI: oai:DiVA.org:umu-166784DiVA, id: diva2:1382006
Public defence
2020-01-31, Sal A, psykiatriska kliniken, målpunkt F, plan 0, Norrlands universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2020-01-10 Created: 2019-12-31 Last updated: 2020-01-07Bibliographically approved
List of papers
1. Long-term effects of unilateral deep brain stimulation on voice tremor in patients with essential tremor
Open this publication in new window or tab >>Long-term effects of unilateral deep brain stimulation on voice tremor in patients with essential tremor
2019 (English)In: Parkinsonism & Related Disorders, ISSN 1353-8020, E-ISSN 1873-5126, Vol. 60, p. 70-75Article in journal (Refereed) Published
Abstract [en]

INTRODUCTION: 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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Deep brain stimulation, Essential tremor, Long-term evaluation, Voice tremor
National Category
Neurology Otorhinolaryngology
Research subject
Neurosurgery; Oto-Rhino-Laryngology
Identifiers
urn:nbn:se:umu:diva-152704 (URN)10.1016/j.parkreldis.2018.09.029 (DOI)000466258400013 ()30297208 (PubMedID)
Available from: 2018-10-19 Created: 2018-10-19 Last updated: 2019-12-31Bibliographically approved
2. Voice Tremor Response to Deep Brain Stimulation in Relation to Electrode Location in the Posterior Subthalamic Area
Open this publication in new window or tab >>Voice Tremor Response to Deep Brain Stimulation in Relation to Electrode Location in the Posterior Subthalamic Area
2019 (English)In: World Neurosurgery: X, ISSN 2590-1397, Vol. 3, p. 1-9, article id 100024Article in journal (Refereed) Published
Abstract [en]

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 tremorimproved 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.

National Category
Other Medical Sciences not elsewhere specified
Research subject
Neurosurgery; Oto-Rhino-Laryngology
Identifiers
urn:nbn:se:umu:diva-158712 (URN)10.1016/j.wnsx.2019.100024 (DOI)2-s2.0-85063299409 (Scopus ID)
Projects
Röst och tal efter djup hjärnstimulering för patienter med Parkinsons sjukdom och essentiell tremor
Available from: 2019-05-08 Created: 2019-05-08 Last updated: 2020-01-07Bibliographically approved
3. Unilateral Left Deep Brain Stimulation of the Caudal Zona Incerta Is Equally Effective on Voice Tremor as Bilateral Stimulation: Evidence from 7 Patients with Essential Tremor
Open this publication in new window or tab >>Unilateral Left Deep Brain Stimulation of the Caudal Zona Incerta Is Equally Effective on Voice Tremor as Bilateral Stimulation: Evidence from 7 Patients with Essential Tremor
2018 (English)In: Stereotactic and Functional Neurosurgery, ISSN 1011-6125, E-ISSN 1423-0372, Vol. 96, no 3, p. 157-161Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Bilateral stimulation, Caudal zona incerta, Deep brain stimulation, Essential tremor, Unilateral stimulation, Voice tremor
National Category
Neurology Other Medical Sciences not elsewhere specified
Research subject
Oto-Rhino-Laryngology; Neurosurgery
Identifiers
urn:nbn:se:umu:diva-150140 (URN)10.1159/000489938 (DOI)000441205500004 ()29975951 (PubMedID)
Available from: 2018-07-10 Created: 2018-07-10 Last updated: 2019-12-31Bibliographically approved
4. The effects of deep brain stimulation on speech intelligibility in persons with essential tremor
Open this publication in new window or tab >>The effects of deep brain stimulation on speech intelligibility in persons with essential tremor
2020 (English)In: Journal of Speech, Language and Hearing Research, ISSN 1092-4388, E-ISSN 1558-9102, Vol. 63, no 2, p. 456-471Article in journal (Refereed) Published
Abstract [en]

Purpose: To investigate how deep brain stimulation (DBS) of the caudal zona incerta (cZi) affects speech intelligibility in persons with essential tremor (ET).

Method: Thirty-five participants were evaluated: off stimulation, on chronic stimulation optimized to alleviate tremor, and during unilateral stimulation at increasing amplitude levels. At each stimulation condition, the participants read 10 unique nonsense sentences from the Swedish Test of Intelligibility. Two listeners, blinded to stimulation condition, transcribed all recorded sentences orthographically in a randomised procedure. A mean speech intelligibility score for each patient and stimulation condition was computed, and comparisons were made between scores off- and on stimulation.

Results: Chronic cZi-DBS had no significant effect on speech intelligibility, and there was no difference in outcome between bilateral and unilateral treatments. During unilateral stimulation at increasing amplitudes, nine participants demonstrated deteriorating speech intelligibility. These nine participants were on average older and had more superior contacts activated during the evaluation compared with the participants without deterioration.

Conclusions: Chronic cZi-DBS, optimized for tremor suppression, does not generally affect speech intelligibility in persons with ET. Furthermore, speech intelligibility may be preserved in many individuals, even when stimulated at high amplitudes. Adverse effects of high-amplitude unilateral stimulation observed in this study were associated with stimulation originating from a more superior location, as well as with the participants’ age. These results, highlighting age and stimulation location as contributing to speech intelligibility outcomes were, however, based on a limited number of individuals experiencing adverse effects with high-amplitude stimulation and should, therefore, be interpreted with caution.

Keywords
caudal zona incerta, deep brain stimulation, essential tremor, posterior subthalamic area, speech intelligibility
National Category
Neurology
Research subject
Neurosurgery
Identifiers
urn:nbn:se:umu:diva-166782 (URN)10.1044/2019_JSLHR-19-00014 (DOI)
Available from: 2019-12-30 Created: 2019-12-30 Last updated: 2020-02-28
5. Speech function following deep brain stimulation of the caudal zona incerta: effects of habitual and high-amplitude stimulation
Open this publication in new window or tab >>Speech function following deep brain stimulation of the caudal zona incerta: effects of habitual and high-amplitude stimulation
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Purpose: To investigate to what extent deep brain stimulation (DBS) of the caudal zona incerta (cZi) affects speech function in persons with essential tremor (ET).

Method: fourteen participants with ET were evaluated: off stimulation (OFF), with habitual stimulation optimized to treat the motor symptoms of ET (ON), and during unilateral stimulation at increasing amplitudes. At each stimulation condition, the participants read three 16-word sentences designed to elicit a variety of articulatory movements. Two listeners made consensus ratings of overall speech function, articulation, and voice using a visual sort and rate method (VISOR). Rated function OFF and ON as well as during unilateral stimulation at the individual maximal amplitude level (MAX) was compared with Friedman nonparametric tests. The effects of bilateral and unilateral stimulation for the five participants treated with bilateral cZi-DBS were compared on a descriptive level.

Results: Habitual cZi-DBS had no significant group-level effect on any of the investigated speech parameters. Articulation was adversely affected by MAX stimulation, and decreased articulation was associated with more medially located electrode contacts. Bilateral and unilateral stimulation were indicated to have similar effects on speech function.

Conclusions: Habitual cZi-DBS did not have any systematic adverse effects on speech function, but response to stimulation was heterogeneous. Unilateral high-amplitude stimulation was found to have more consistent negative effects, particularly on articulation. Decreased articulatory function was associated with high-amplitude stimulation of medially located contacts, suggestive of cerebello-rubrospinal involvement. These results were, however, based on a limited number of individuals and should, therefore, be interpreted with caution.

Keywords
caudal zona incerta, deep brain stimulation, essential tremor, posterior subthalamic area, speech function
National Category
Neurology
Identifiers
urn:nbn:se:umu:diva-166783 (URN)
Available from: 2019-12-30 Created: 2019-12-30 Last updated: 2020-01-03Bibliographically approved

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