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

Blomstedt

2019

World Neurosurgery: X

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

Section: Discussionsupporting

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

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Voice Tremor Response to Deep Brain Stimulation in Relation to Electrode Location in the Posterior Subthalamic Area

Blomstedt

2019

World Neurosurgery: X

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“…The cZi is a small nucleus targeted in-between the red nucleus (Rn) and the posterior tip of the STN (pSTN) at the depth where the Rn has its maximal diameter (see Figure 1; Blomstedt, 2018), and this has been the DBS target of choice for ET at Umeå University Hospital since 2004. Previous investigations into the effects of DBS in the cZi have shown that unilateral cZi DBS can have a positive effect on voice tremor (Sandström et al, 2019b(Sandström et al, , 2018, also in the long term (Sandström et al, 2019a), and that habitual cZi DBS, optimized to treat the motor symptoms of ET, does not affect speech intelligibility (Sandström et al, 2020). However, in the same clinical population, it was also noted that speech intelligibility might deteriorate during highamplitude stimulation from electrode contacts higher up in the PSA (Sandström et al, 2020) and that successful voice tremor management may depend on the exact location of the electrode within the cZi (Sandström et al, 2019b); results that indicate that speech and voice outcomes could vary depending on targeting precision.…”

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confidence: 99%

Speech Function Following Deep Brain Stimulation of the Caudal Zona Incerta: Effects of Habitual and High-Amplitude Stimulation

Schalling

et al. 2021

J Speech Lang Hear Res

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Purpose Deep brain stimulation (DBS) is often successful in alleviating motor symptoms of essential tremor (ET); however, DBS may also induce adverse speech effects. The caudal zona incerta (cZi) is a promising DBS target for tremor, but less is known about the consequences of cZi DBS for speech. This preliminary study examined how habitual cZi DBS and cZi stimulation at high amplitudes may affect speech function in persons with ET. Method Fourteen participants with ET were evaluated: off stimulation, on habitual cZi DBS, and with unilateral cZi stimulation at increasing stimulation amplitudes. At each stimulation condition, the participants read three 16-word sentences. Two speech-language pathologists made audio-perceptual consensus ratings of overall speech function, articulation, and voice using a visual sort and rate method. Rated functions when off stimulation, on habitual cZi DBS, and at maximal-amplitude stimulation were compared using Friedman nonparametric tests. For participants with bilateral habitual DBS ( n = 5), the effects of bilateral and unilateral stimulation were described in qualitative terms. Results Habitual cZi DBS had no significant group-level effect on any of the investigated speech parameters. Maximal-amplitude stimulation had a small but significant negative effect on articulation. Participants with reduced articulatory precision ( n = 9) had more medially placed electrodes than the nonaffected group ( n = 5). Bilateral and unilateral left stimulation had comparable effects on speech. Conclusions Findings from this preliminary study of cZi DBS indicate that speech is generally not affected by stimulation at habitual levels. High-amplitude cZi stimulation may, however, induce adverse effects, particularly on articulation. Instances of decreased articulatory function were associated with stimulation of more medial electrode contacts, which could suggest cerebello-rubrospinal involvement.

“…Voice tremor is also a common symptom of ET that can interfere with communication and adversely affect quality of life (Chandran & Pal, 2013;Louis & Gerbin, 2013). While voice tremor may improve with DBS (Avecillas-Chasin et al, 2019;Hägglund et al, 2016;Matsumoto et al, 2016;Sandström et al, 2018Sandström et al, , 2019, stimulation-induced dysarthria is a frequently reported adverse effect, especially in those treated bilaterally (Alomar et al, 2017). DBS has been found to cause imprecise articulation and a slow speech rate (Mücke et al, 2014(Mücke et al, , 2018Plaha et al, 2011) in persons with ET and induce symptoms that can generally be described as characteristic of ataxic or mixed ataxic-spastic dysarthria (Matsumoto et al, 2016), but with "preserved intelligibility" (Matsumoto et al, 2016;Plaha et al, 2011).…”

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The Effects of Deep Brain Stimulation on Speech Intelligibility in Persons With Essential Tremor

Blomstedt

et al. 2020

J Speech Lang Hear Res

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Purpose The aim of this study was to investigate how deep brain stimulation (DBS) of the caudal zona incerta (cZi) affects speech intelligibility in persons with essential tremor. 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 randomized 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 essential tremor. 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.