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Effects of Subthalamic Nucleus Deep Brain Stimulation on Bilateral Vocal Cord Paralysis in Parkinson's Disease

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Effects of Subthalamic Nucleus Deep Brain Stimulation on Bilateral Vocal Cord Paralysis in Parkinson’s disease

Elsa Arocho-Quinones MD1,2, Chris Sheridan RN2, Jonathan M. Bock MD FACS3, Brad Hiner MD4, Peter Pahapill MD PhD1,2

1Department of Neurosurgery, U.S. Department of Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295; 2Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI 53226; 3Department of Otolaryngology and Communication Science, Medical College of Wisconsin, Milwaukee, WI 53226; 4Department of Neurology, Medical College of Wisconsin, Milwaukee, WI 53226

Introduction

The role of laryngeal dysfunction in the development of speech disorders in Parkinson’s disease (PD) is being increasingly recognized, however, reports on stridor and bilateral vocal cord paralysis (VCP) in PD  are rare and studies on the effects of deep brain stimulation on bilateral vocal cord paralysis are lacking.

Herein, we present a case of stridor secondary to bilateral VCP in a patient with PD. Our goal was to assess the effects of subthalamic nucleus deep brain stimulation (STN-DBS) on vocal cord function and to correlate these effects with those on motor symptoms at different stimulation settings.

 

Case Report

History of Present Illness:

The patient is a 51 year old male with progressive Parkinson’s disease diagnosed 10 years ago and who’s symptoms began with tremors on the left side. His tremors progressed to grade 2/4 tremors, greater on his left than right side. He also developed motor fluctuations with bradykinesia, rigidity, and dyskinesia especially with head movements. He had imbalance problems and speech difficulties which seemed to respond to medication. He also reported intermittent shortness of breath, noisy breathing, reflux, dysphagia worse with solids than liquids, and frequent urination worse at night.

Prior to placement of his right-sided STN-DBS electrode he was noticed to have noisy breathing with stridor which he reported had started 9 months prior but had gotten worse after stopping his PD medications in preparation for surgery. Post-operatively, he was referred to a pulmonary specialist and subsequently to Otolaryngology for evaluation of airway obstruction. He was found to have bilateral vocal cord paralysis and a tracheostomy was recommended. One month after his right DBS electrode placement he underwent placement of the left STN-DBS electrode. Ten days later, he underwent implantation of a dual chamber subclavicular pulse generator with connection to bilateral STN-DBS electrodes under general anesthesia followed by tracheostomy placement. Three weeks later he returned to clinic for the initial programming of his STN-DBS system.

Medications: Amantadine, carbidopa/levodopa, rasagiline, ropinirole, and tamsulosin.

 

Methods:

The patient was evaluated following initiation of bilateral subthalamic nucleus deep brain stimulation (STN-DBS) at several intervals during a period of 11 months.

Outcomes were measured by direct observation of vocal cord function via transnasal laryngoscopy during clinic visits, assessment of reduction in antiparkinsonian medication requirement, and evaluation of UPDRS (Unified Parkinson’s Disease Rating Scale) motor scores in the medication-off, medication-on, stimulation-off, and stimulation-on states at various intervals post-operatively. Effects of short term low frequency stimulation with 60Hz were compared to stimulation at 150 Hz. 

Standardized scales were used to convert the dosing of his antiparkinsonian drug regimen into levodopa equivalent doses (LEDs).

Laryngeal function assessments were performed in conjunction with a speech-language pathologist. Digital videostroboscopy was used to record laryngeal motion while the patient was asked to sniff or inhale and then phonate a range of utterances at a variety of pitches and volumes.

Diagnostic Studies:

Pulmonary function testing: Spirometry and flow volume loop were normal. Lung volumes demonstrated mild air trapping. Diffusion capacity was only mildly reduced. Airway resistance was increased. Administration of an inhaled bronchodilator did not lead to significant improvement in spirometry.

CT neck: No evidence of mass or lymphadenopathy. Bilateral vallecula and pyriform sinuses are unremarkable. Both vocal cords are symmetrical.

Baseline evaluation of upper airway via transnasal laryngoscopy (Fig. 1A) revealed bilateral vocal fold paralysis at the paramedian position with intermittent twitch movement of the right vocal process but no significant movement of the left true vocal cord (TVC).

Results:

A baseline evaluation in the MED-OFF, STIM-OFF state yielded a UPDRS-III score of 57. There was a marked improvement in UPDRS-III scores after STN-DBS initiation (Table 1). His baseline antiparkinsonian drug regimen totaled 1600mg levodopa equivalent dose (LED) daily and this was reduced by 82% at 105 days post stimulation.

A baseline laryngoscopic evaluation revealed bilateral paralysis of vocal cord abduction. At 105 days post STN-DBS, the right TVC reached a maximal abduction of 2-3mm on inhalation but no movement of the left TVC.

On day 225 post STN-DBS, his UPDRS-III score was 32 with STIM-ON. After turning the stimulation off (STIM-OFF) for 2hrs, his UPDRS-III score was 74, and there was worsening in the abduction of the right TVC with an overall reduction in the tone of the vocal folds (Figure 1C). His speech also became effortful, garbled, and unintelligible during this time.

On day 328, the maximal vocal cord abduction was 5mm with stimulation at 150Hz and no significant difference in laryngeal motion was observed after short term stimulation at 60Hz.

Conclusions:

In the absence of head, neck, or chest pathology, the vocal cord paralysis in our patient was considered secondary to progression of Parkinson's disease (PD).

Bilateral STN-DBS resulted in improved motor scores, decreased medication requirement, and improvement in the abduction of the right TVC on inhalation although still insufficient for safe decannulation. Short term low frequency stimulation had no significant effect on vocal cord abduction.

As these results suggest a role for DBS in the neuromodulation of PD-induced vocal cord paralysis, a potentially life threatening condition, we will continue to evaluate the effects of DBS at various frequencies in an attempt to better target axial motor function and laryngeal control.