Location of Deep Brain Stimulation in Parkinson's Disease Patients Affects Postoperative Voice Quality

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There is no consensus about whether the location of deep brain stimulation (DBS) affects voice-related outcomes in patients with Parkinson's disease—or even whether that question should be a concern. Some investigators believe it's important to understand how the location of DBS affects speech and try to target voice dysfunction during preoperative planning. Others view speech dysfunction as a necessary tradeoff for improved motor and neuropsychological outcomes.

Over the past several years, Massachusetts General Hospital has offered pre- and postoperative voice evaluations as part of the movement disorders DBS program. Mark Richardson, MD, PhD, director of Functional Neurosurgery in the Department of Neurosurgery, and colleagues have observed that the location of stimulation within the subthalamic nucleus (STN) is associated with perceptual, acoustic and aerodynamic measures of voice function. They report their findings in Neurosurgery.

Study Methods

The team identified 14 patients with Parkinson's disease who underwent bilateral STN DBS between September 2015 and September 2018 and had voice evaluations preoperatively and six to 35 months postoperatively.

Preoperatively, all patients were diagnosed with hypokinetic dysarthria, a specific motor speech disorder characterized by various deficits in fluency, phonation (physical production of speech), articulation and rhythm/stress/intonation. Some had additional diagnoses such as primary muscle tension dysphonia or vocal fold atrophy.

Perceptual Measures

Perceived severity of voice pathology was measured on a 0–100 visual analog scale. Voice severity improved, linearly and significantly, when electrodes were placed in the most anterior locations of the sensorimotor region of the left STN. Conversely, the severity worsened most when the contacts were in the most posterior locations. Location of contacts accounted for approximately 40% of the change in voice severity.

No previous study of DBS effects on voice has analyzed active contact locations in three-dimensional space.

Perceptual Measures

Perceptual measures tested included roughness, breathiness, hoarseness, strain, low pitch and high pitch. Low pitch was the only one that worsened significantly after surgery, and the change was not location-dependent.

Acoustic Measures

This study was also the first to evaluate the effects of DBS on cepstral (acoustic) voice measures, which reflect sound frequencies and thus the severity of dysphonia.

Cepstral peak prominence, a simple frequency measure, was not correlated with stimulation location. However, improvement in cepstral spectral index of dysphonia (CSID), a multiparameter score, was significantly correlated with anterior stimulation in the left STN.

Aerodynamic Measures

Improvements in phonatory airflow and shortness of breath during speech were also associated with more anterior stimulation in the left STN.

Continued Research Needed

Both CSID and the severity of vocal pathology are related to vocal fold vibration, which is fueled by adequate respiratory drive. More anterior electrode placement for DBS might have improved respiratory drive, leading to improved vocal quality for some patients.

Variation in the medial–lateral and dorsal-ventral positions in the left STN and variation in any direction on the right did not correlate with any voice outcome. The laterality of these findings is intriguing and warrants further research.

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