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Objective: To characterize changes in speech and voice parameters in patients with Parkinson’s disease (PD) after globus pallidus interna (GPi) deep brain stimulation (DBS).
Background: The majority of PD patients develop voice and speech disorders in their disease course, characterized by weak voice, monotonous pitch and loudness, short rushes of speech, and imprecise articulation (termed hypokinetic dysarthria). PD patients have variable speech changes following STN-DBS, but effects of GPi-DBS on speech performance in PD remain unclear.
Design/Methods: We used the prospective University of Florida INFORM database and chart review to identify PD patients who underwent bilateral GPi-DBS from 2006–2019. We collected demographics, experiences of daily living, motor and speech function. Our speech evaluation targeted speech subsystem domains (respiratory, laryngeal, velopharyngeal, orofacial, rate, prosody, rhythm, naturalness) and overall intelligibility, with severity ratings on a Likert scale ranging from 0 (no dysfunction) to 7 (anarthric). Patients missing pre- or postsurgical evaluations were excluded. We compared clinical evaluations between baseline and 6–12 months postsurgically.
Results: We identified 31 patients of which 58% were male (n=18), with mean age at surgery of 63.7±9.6 years. Baseline Unified Parkinson Disease Rating Scale (UPDRS) part III mean total score off medications was 41.2±10.4, with mean baseline speech subscore of 1.4±0.7. We examined speech subsystem domains and found significant worsening in the following parameters after bilateral GPi-DBS: laryngeal, velopharyngeal, prosody and naturalness (p<0.05). No significant difference was found in overall intelligibility between pre- (98.4±2.8%) and post (98.5±3.7%) GPi-DBS (p=0.46).
Conclusions: We found that GPi-DBS worsened several modalities of Parkinsonian speech without compromising overall speech intelligibility. This pattern appears different from impact of STN-DBS, whereby deterioration of articulation, reduced intelligibility and induction of spastic dysarthria are more commonly seen. Speech function may be less compromised after GPi-DBS. More investigation is needed to evaluate differential pathophysiological mechanisms of stimulation-related dysarthria.