Objective: To establish different clusters with distinctive speech characteristics in people with Parkinson’s disease (PwPD) who experience stimulation-induced dysarthria (SID).

Background: To date, the effect of deep brain stimulation (DBS) on speech function has been assessed in many studies, indicating that DBS may improve or worsen speech function independent of the effect on motor functions [1,2]. Previous data suggest that distinct subtypes of disturbed speech can be observed in PwPD[3]. 

Method: We present a dataset from a prospective study with 25 PwPD who had received a monopolar review aiming to evoke SID. Stimulation for each contact was increased until the onset of SID or other intolerable side effects. A German standard reading text was recorded under the stimulation parameters that induced SID as well as under inactivated DBS. The participant‘s speech function was subsequently evaluated blindly by two independent raters using the Assessment of Motor Speech for Dysarthria (AMSD) [4] and the Grade of dysphonia, Roughness, Breathiness, Asthenia and Strain (GRBAS) scale [5].

We then calculated change scores to assess the differences between the DBS-OFF condition and the conditions in which SID was provoked.

Following the methodology used by Tsuboi et al. in 2015, we conducted an exploratory factor analysis to investigate the role of each scale item. The generalized least-squares method was applied to the different rating items to identify underlying factors. This analysis was enhanced with Varimax rotation. Following this, a cluster analysis using Ward’s method was conducted on the factor scores to group samples into clusters. This classification was based on the similarity of their predominant speech and voice characteristics.

Results: We observe two distinct clusters signifying DBS induced speech dysfunction. We observe a cluster with strained speech, that is characterized by short rushes of speech, voice tremor, hypernasality and abnormal rate. Secondly, we report a cluster with factors signifying corticobulbar speech affection with roughness, strain and imprecise consonants among others.

Conclusion: Our findings highlight the presence of unique DBS-induced Parkinsonian dysarthria subtypes, implying that different underlying anatomical and pathological factors might be at play.

References: References:
1. Frost, E., Tripoliti, E., Hariz, M. I., Pring, T. & Limousin, P. Self-perception of speech changes in patients with Parkinson’s disease following deep brain stimulation of the subthalamic nucleus. International Journal of Speech-Language Pathology 12, 399–404 (2010).
2. Tanaka, Y. et al. Longitudinal Speech Change After Subthalamic Nucleus Deep Brain Stimulation in Parkinson’s Disease Patients: A 2-Year Prospective Study. J Parkinsons Dis 10, 131–140 (2020).
3. Tsuboi, T. et al. Distinct phenotypes of speech and voice disorders in Parkinson’s disease after subthalamic nucleus deep brain stimulation. J Neurol Neurosurg Psychiatry 86, 856–864 (2015).
4. Nishio M. Assessment of motor speech disorders (AMSD) Tokyo: Interuna . Publishers Inc; 2004. [(in Japanese)]
5.Hirano, M., Psycho-acoustic evaluation of voice, New York: Springer-Verlag. 1981.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cluster-analysis-of-stimulation-induced-dysarthria-subtypes-in-people-with-parkinsons-disease-and-subthalamic-deep-brain-stimulation/