Development of a nerve conduction technique for the recurrent laryngeal nerve

Immediate effect of recurrent laryngeal nerve stimulation in patients with idiopathic unilateral vocal fold paralysis

BACKGROUND

There is a lack of effective treatment for idiopathic unilateral vocal fold paralysis (IUVFP). A better phonation was reported by patients after laryngeal nerve stimulation during our clinical examination.

OBJECTIVES

This study aims to investigate immediate effect of recurrent laryngeal nerve (RLN) stimulation on phonation in patients with IUVFP.

MATERIAL AND METHODS

Sixty-two patients with clinically identified IUVFP underwent RLN stimulation with needle electrodes. Laryngoscopy, acoustic analysis, and voice perception assessment were performed for quantitative comparison of vocal function and voice quality before and after the intervention.

RESULTS

Laryngoscopic images showed a larger motion range of the paralyzed vocal fold (p < .01) and better glottal closure (p < .01) after RLN stimulation. Acoustic analysis revealed that the dysphonia severity index increased significantly (p < .01) while the jitter and shimmer decreased after the intervention (p < .05). According to perceptual evaluation, RLN stimulation significantly increased RBH grades in patients with IUVFP (p < .01). Furthermore, the improvement in voice perception had a moderate positive correlation with the decrease in the glottal closure.

CONCLUSIONS AND SIGNIFICANCE

This study shows a short-term improvement of phonation in IUVFP patients after RLN stimulation, which provides proof-of-concept for trialing a controlled delivery of RLN stimulation and assessing durability of any observed responses.

Recurrent laryngeal motor nerve conduction studies in a rat model: Establishing an objective measure for investigating laryngeal innervation

INTRODUCTION/AIMS

Disease or injury can cause neuromuscular changes to the larynx that can affect voice, breathing, and swallowing. Motor nerve conduction studies have had limited use in the study of laryngeal neurophysiology, despite their importance in other anatomic sites. The aim of this study was to explore the feasibility of performing recurrent laryngeal motor nerve conduction studies (rlMNCS) in a rat model.

METHODS

rlMNCS were performed in 15 rats under anesthesia. A bipolar stimulating electrode was placed on the recurrent laryngeal nerve (RLN) 5 mm below the cricoid cartilage. Via direct laryngoscopy, a recording electrode was placed transorally into the thyroarytenoid muscle. The RLN was maximally stimulated to determine the compound muscle action potential (CMAP). Three consecutive trials were averaged.

RESULTS

The mean stimulating threshold to the RLN to achieve a CMAP from the thyroarytenoid was 1.7 ± 0.6 mA. RLN stimulation caused a visible adductor twitch of the vocal fold in all animals. The mean negative amplitude was 2.0 ± 0.8 mV, and the total area was 1.0 ± 0.4 mV ms. The CMAP latency and negative duration were 1.0 ± 0.1 ms and 0.9 ± 0.2 ms, respectively.

DISCUSSION

rlMNCS are feasible and may be useful in understanding laryngeal neurophysiology with disease or injury. This work could provide a tractable animal model for studying and monitoring treatment of neuromuscular conditions affecting voice, breathing, and swallowing.

Third branchial cleft cyst as a cause of hoarseness: a case report

Third branchial cleft cyst is a rare congenital disease of the neck. It presents as a painless mass that develops rapidly in the neck following an infection. This is the first case report of recurrent laryngeal nerve palsy caused by a third branchial cleft cyst. A 30-year-old woman presented with a 3-month history of hoarseness as her only symptom; she had no pain, fever, dysphagia, dyspnoea, or palpable neck mass. Laryngoscopy revealed that her right vocal cord was paralyzed. Computed tomography and magnetic resonance imaging revealed a cystic mass in the right tracheoesophageal groove that was closely associated with the trachea. Intraoperatively, the cyst was found not to originate from the thyroid or trachea, but it was compressing the right recurrent laryngeal nerve. The hoarseness resolved the day after the cyst was removed.

Development of In-Office Laryngeal Nerve Conduction Studies: Computed Tomography and Cadaveric Study

OBJECTIVES/HYPOTHESIS

In-office recurrent laryngeal nerve conduction studies (NCSs) are a technique that can potentially provide information about laryngeal innervation. NCS is essential in the management of other neuropathies including carpal tunnel syndrome and spinal cord injury. We hypothesize that laryngeal NCS may have similar utility in managing patients with vocal fold paralysis, atrophy, and neurodegenerative disease. NCSs are technically challenging because they require transcervical stimulation of the recurrent laryngeal nerve (RLN). This study combines radiographic data with cadaveric dissection to describe the anatomic parameters for optimal RLN stimulation.

STUDY DESIGN

Radiographic and Cadaveric Study.

METHODS

Fifty computed tomography scans were reviewed to determine the dimensions for ideal needle electrode placement. These values were compared to measurements from 12 fresh human cadaveric neck dissections. Ultrasound imaging was utilized in select cases. The neck was dissected to assess the accuracy of electrode placement.

RESULTS

Radiographically, the mean transcervical depth to the RLN was 33.2 mm ± 8.3 mm in males versus 29.4 mm ± 9.4 mm in females. The working space between the lateral trachea and carotid artery was 15.3 mm ± 3.6 mm on the right and 14.1 mm ± 2.9 mm on the left. After placement of stimulating electrodes into the cadaveric neck, the electrode tips were consistently within 8 mm of the RLN. Ultrasound guidance improved placement accuracy of the stimulating electrode.

CONCLUSIONS

Laryngeal NCSs can provide detailed and objective information about laryngeal innervation that could dramatically improve the management of various neuropathies. In-office NCSs require technical precision, and this study describes anatomic factors that may affect the feasibility of performing this technique.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:1566-1569, 2021.

Compound Motor Action Potential Measures Acute Changes in Laryngeal Innervation

Objective:

Vocal fold paralysis is caused by injury to the recurrent laryngeal nerve (RLN). Current clinical measures of laryngeal innervation are often nonquantitative. Compound motor action potentials (CMAP) measure motor innervation. The goal of this study was to determine whether CMAP can quantify laryngeal innervation following acute nerve injury.

Study Design:

Animal study.

Methods:

Twelve canine hemilaryngeal preparations were used. The RLN was serially stimulated with increasing intensities until the nerve was maximally stimulated. The CMAP amplitude was measured for each intensity stimulation and correlated. Next, the RLN was incompletely transected, and the reduction in CMAP amplitude was correlated to the percentage of transected axons. The percentage of transected axons was determined using horseradish peroxidase (HRP) staining.

Results:

Combining all hemilaryngeal preparations, the submaximal stimulation of the RLN linearly correlated with the resultant CMAP amplitude (r = 0.83; 95% CI, 0.76-0.88). Following partial RLN transection, the percentage of remaining axons linearly correlated with the CMAP amplitude (r = 0.87; 95% CI, 0.34-0.98).

Conclusions:

CMAP amplitude is a quantitative measure that may correlate with the degree of vocal fold innervation in canines. Following RLN injury, CMAP may help clinicians quantify the number of intact axons, assess the likelihood of recovery, and counsel patients on their prognosis.

Pathological classification of equine recurrent laryngeal neuropathy

Recurrent Laryngeal Neuropathy (RLN) is a highly prevalent and predominantly left-sided, degenerative disorder of the recurrent laryngeal nerves (RLn) of tall horses, that causes inspiratory stridor at exercise because of intrinsic laryngeal muscle paresis. The associated laryngeal dysfunction and exercise intolerance in athletic horses commonly leads to surgical intervention, retirement or euthanasia with associated financial and welfare implications. Despite speculation, there is a lack of consensus and conflicting evidence supporting the primary classification of RLN, as either a distal ("dying back") axonopathy or as a primary myelinopathy and as either a (bilateral) mononeuropathy or a polyneuropathy; this uncertainty hinders etiological and pathophysiological research. In this review, we discuss the neuropathological changes and electrophysiological deficits reported in the RLn of affected horses, and the evidence for correct classification of the disorder. In so doing, we summarize and reveal the limitations of much historical research on RLN and propose future directions that might best help identify the etiology and pathophysiology of this enigmatic disorder.

Compound Motor Action Potential Quantifies Recurrent Laryngeal Nerve Innervation in a Canine Model

Objective:

The compound motor action potential (CMAP) is the summated action potential from multiple muscle fibers activated by a single nerve impulse. The utility of laryngeal muscle CMAP for quantifying innervation following recurrent laryngeal nerve (RLN) injury was investigated.

Method:

In a series of 21 canine hemi-laryngeal preparations, RLNs were exposed and a stimulating electrode placed. Maximum CMAP amplitudes and area under the curve from the thyroarytenoid (TA) muscles were obtained at baseline and at 6 months following injury to the RLN. Injury mechanisms included crush, stretch, cautery, and complete transection with microsuture repair.

Results:

Prior to injury, baseline CMAP amplitudes and area under the curve were 15.81 mV and 15.49mVms, respectively. Six months following injury, CMAP amplitude and area under curve were 105.1% and 102.1% of baseline for stretch, 98.7% and 112.7% for crush, 93.3% and 114.3% for cautery. The CMAP amplitude and area under the curve in the transection/repair group had a 54.3% and 69.4% recovery, respectively, which were significantly different than baseline ( P < .01, P < .05). These values were correlated with vocal fold motion.

Conclusion:

The CMAP is a measure of vocal fold innervation. The technique could be further developed for clinical and experimental applications.