Management of Recurrent Laryngeal Nerve Paralysis

Evaluation

The classic presentation seen in clinical care is altered voice with or without some level of swallowing difficulty due to unilateral vocal fold paralysis (UVFP) after thyroid surgery. This may happen even despite an intact RLN and confirmatory intraoperative neural monitoring (IONM) findings at the completion of surgery. Sahli et al. found this rate to be as high as 18.8% with age ≥ 50 years as an independent risk factor for postoperative dysphonia and/or dysphagia. Although RLN injury may seem like the first logical culprit, thoughts should be given to alternative diagnoses. The chart should be reviewed for preoperative evaluation to ensure that there was no preexisting dysfunction before surgery. Otherwise, an intubation-related injury by compression of the nerve microcirculation may be considered but is probably a rare occurrence with a reported incidence of 0.08%.

UVFP after thyroidectomy most commonly presents with a breathy, weak voice. Projection is limited, and the voice is easily fatigued; there may be a subjective sense of shortness of breath during phonation. In addition to dysphonia, patients may also experience dysphagia with or without aspiration. One should therefore inquire about issues of choking or coughing while eating or drinking as well as any history of interval pneumonia. The voice is evaluated by both the clinician and the patient. The clinician performs a perceptual voice assessment most commonly using the GRBAS scale (grade, roughness, breathiness, asthenia, strain) or CAPE-V (consensus auditory perceptual evaluation of voice) tool to determine voice quality. Additionally, acoustic measures, such as jitter, shimmer, and noise-to-harmonic ratio, may be collected. The patient is asked to complete a voice handicap assessment survey, most commonly the Voice Handicap Index-10. These tools help establish a baseline from which progress can be tracked and the success of interventions can be measured. A comprehensive head and neck examination should follow. This includes assessment of cranial nerve function with special attention to the vagus nerve. The neck should be palpated for any lymphadenopathy, neck masses, or laryngotracheal malformations.

Videolaryngoscopy

Videolaryngoscopy is essential for the examination of the larynx in the dysphonic patient. Updated clinical practice guidelines published by the American Academy of Otolaryngology—Head and Neck Surgery state that laryngoscopy should be performed on any patient for which dysphonia does not improve or resolve within 4 weeks. For the postsurgical candidate in whom vocal fold paralysis is predicted, more expeditious laryngoscopy is warranted. Flexible laryngoscopy allows examination of the larynx in its physiologic position and during respiratory and phonatory tasks while providing magnified, high-resolution images of the larygopharyngeal mucosa. Videolaryngoscopy with the addition of stroboscopy provides further insight into vocal fold mobility and vibratory function as well as symmetry and completeness of glottic closure.

Endoscopic laryngeal examination should focus on any asymmetries in anatomy or movement. Playback may be slowed, viewed frame by frame, or even arranged as a mosaic to highlight any irregularities of motion. Repeated phonatory tasks may induce vocal fatigue and make subtle vocal fold paresis more apparent. Common tasks include an alternating /i/ vowel followed by a gentle sniff in repetition. For the identification of recurrent laryngeal nerve (RLN) injury the sine qua non is the absence of volitional motion (abduction of the vocal process) from the rested position. The glissando maneuver, sliding from low to high pitch and then back down to low pitch requires activation of the cricothyroid muscle by way of the superior laryngeal nerve (SLN). SLN paresis may present as a rotation of the posterior larynx toward the side of injury during a glissando maneuver. Videostroboscopy may highlight other features that may support the diagnosis of vocal fold paresis. Parameters found to be important include ipsilateral vocal fold thinning, vocal fold bowing, reduced movement and kinesis, and a phase lag of the vibratory waves. It is not uncommon that patients with unilateral vocal fold paralysis (UVFP) experience dysphagia and may be at increased risk of aspiration from glottal incompetence. Patients who report dysphagia or who have a potentially unsafe swallow often get a modified barium swallow (MBS) study and/or a fiberoptic endoscopic evaluation of swallowing (FEES). FEES may be performed after a videolaryngoscopy. During a FEES examination, the laryngopharyngeal anatomy is observed before and after swallowing. The flexible laryngoscope tip is positioned in the velopharyngeal inlet to provide uninhibited observation of the oropharyngeal and pharyngeal phases of swallowing. Baseline secretions are noted. During the swallow, the patient is observed for penetration (entry of contents into the larynx or laryngeal vestibule) or aspiration (passage of contents beyond the vocal folds and into the tracheobronchial tree). If abnormalities are discovered, the clinician can conduct trial interventions in real time such as chin tuck or breath hold. Aviv and colleagues added sensory testing as part of the endoscopic swallowing sensory testing (FEESST) examination using calibrated pulses of air to elicit the laryngeal adductor reflex. Tabaee et al. showed significantly higher rates of dysphagia in patients with decreased pharyngeal squeeze, decreased laryngopharyngeal sensation, and an absent laryngeal adductor reflex.

Laryngeal Electromyography

Laryngologists have reported the diagnostic inaccuracy of pure visual assessment of the larynx to diagnose neuromuscular dysfunction to be as high as one-third of cases. This is in comparison to laryngeal electromyography (LEMG), a technique to directly and objectively assess the integrity of laryngeal nerves and muscles. LEMG is a useful tool used as an adjunct to videostroboscopy, helping distinguish between neurologic causes of vocal fold immobility or hypomobility and mechanical causes, such as cricoarytenoid joint fixation. It is also a tool that can help prognosticate return of function in cases of paresis or paralysis and help predict whether patients will respond well to voice therapy alone or will require procedural intervention. The utility of LEMG has been a topic of much debate with sparse evidence-based support. In 2016, a consensus statement on the utility of LEMG for diagnosis and treatment of vocal fold paralysis after recurrent laryngeal neuropathy was published. It concluded that LEMG should be used if prognostic information is sought in a patient with vocal fold paralysis for more than 4 weeks but less than 6 months. In such patients, if they have active voluntary motor unit potential recruitment and polyphasic motor units potentials, recovery is anticipated. Furthermore, use of LEMG in the clinical algorithm led to a change in clinical management by better understanding the diagnosis in 48% of cases reviewed by Munin et al. LEMG in practice may take on a variety of forms from an individual to a team-based approach. Often an electrodiagnostic physician and an otolaryngologist work together to complete this office-based procedure.