Objective: To investigate the effect of thalamic (ventral intermediate nucleus, VIM) and subthalamic (posterior subthalamic area, PSA) deep brain stimulation (DBS) in patients with essential tremor (ET) on speech motor control. We analyze (1) ET patients preoperatively vs. healthy controls, (2) ET patients pre- vs. postoperatively, and (3) PSA- vs. VIM-DBS.

Background: The VIM is the traditional DBS target in ET, while the PSA has recently been suggested as an alternative. However, stimulation-induced dysarthria (SID) is a common side effect of thalamic and subthalamic DBS [1]. The effects of VIM vs. PSA-DBS as well as pre- and postoperative effects on speech have not been explored systematically so far.

Methods: In a prospective, randomized, double-blind crossover design [2], 13 German ET patients were implanted bilaterally with a DBS system, with at least one contact in PSA and VIM. Patients were recorded acoustically before implantation, and with bilateral VIM- and PSA-DBS, and 13 age- and sex-matched healthy controls were included. Speech materials consisted of oral diadochokinesis (DDK) and a read standard text. To capture speech impairment, we analyzed acoustic DDK parameters related to oral and glottal control. Single phrases out of the read text were rated by 25 naive listeners for intelligibility and naturalness. Furthermore, both patients and the attending physician rated the “ability to speak” on a visual analog scale.

Results: Compared to healthy controls, we found reduced intelligibility in ET patients preoperatively. Additionally, articulation rate could be predicted by disease duration but not by age of patients. When comparing patient’s speech before and after implantation, we found a strong effect of DBS on acoustic measures as well as on ratings, indicating a further deterioration of speech. VIM- and PSA-DBS did not differ significantly from each other with regard to acoustic measures and ratings.

Conclusions: Firstly, our data suggest that speech is already impaired in ET patients without DBS. Secondly, speech worsens under DBS in terms of slower articulation rate and reduced glottal and oral control. Thirdly, subthalamic DBS does not differ from thalamic DBS with regard to speech motor control. Therefore, the PSA might serve as an alternative target in ET patients with no further disadvantage regarding SID.

References: [1] Flora ED, Perera CL, Cameron AL, Maddern GJ. Deep brain stimulation for essential tremor: a systematic review. Mov Disord 2010;25(11):1550-9. [2] Barbe MT, Franklin J, Kraus D, et al. Deep brain stimulation of the posterior subthalamic area and the thalamus in patients with essential tremor: study protocol for a randomized controlled pilot trial. Trials 2016;17(1):476.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-effect-of-thalamic-and-subthalamic-deep-brain-stimulation-on-speech-in-patients-with-essential-tremor-a-prospective-randomized-double-blind-crossover-study/