Etiology and Time to Presentation of Unilateral Vocal Fold Paralysis

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.

Recurrent laryngeal nerve recovery patterns assessed by serial electromyography

OBJECTIVES/HYPOTHESIS

Following acute injury to the recurrent laryngeal nerve (RLN), laryngeal electromyography (LEMG) is increasingly being used to determine prognosis for recovery. The LEMG findings change during the recovery process, but the timing of these changes is not well described. In this canine study, LEMGs were obtained serially following model RLN injuries.

STUDY DESIGN

Animal Study.

METHODS

Thirty-six canine RLNs underwent crush (n = 6), complete transection with reanastomosis (n = 6), half-transection half-crush (n = 5), cautery (n = 5), stretch (n = 5), inferior crush (n = 4), or inferior transection with reanastomosis (n = 5) injuries. Injuries were performed 5 cm from cricoid or were 5 cm further inferior. Under light sedation, LEMG of thyroarytenoid muscles was performed monthly for 6 months following injury. At 6 months, spontaneous and induced vocal fold motion was assessed.

RESULTS

Except for the stretch injury, the remaining groups showed very similar recovery patterns. Fibrillation potentials (FPs) and/or positive sharp waves (PSWs; signs of bad prognosis) were seen in all cases at 1 month and lasted on average for 2.26 months (range = 1-4 months). Motor unit potentials of at least 2+ (scale = 0-4+; signs of good prognosis) were seen beginning at 3.61 months (range = 2-6 months). The stretch injury was less severe, with 3 of 5 showing no FPs/PSWs at 1 month; all recovered full mobility. Ten of the 36 thyroarytenoid muscles (27.8%) had 1 electromyograph showing both bad prognosis and good prognosis signs simultaneously at 2 to 4 months postinjury.

CONCLUSIONS

LEMG can be used to predict RNL recovery, but timing is important and LEMG results earlier than 3 months may overestimate a negative prognosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:651-656, 2016.

A rare case of non-surgical vocal cord paralysis: Vocal cord hematoma

Although vocal cord paralysis (VCP) following thyroidectomy is primarily associated with surgical trauma, it is not the sole etiology. Vocal cord paralysis following thyroidectomy can be caused by a vocal cord hematoma with an incidence of 1.4% due to direct injury during orotracheal intubation. In this article, we present a case of VCP caused by vocal cord hematoma. A 32-year-old male patient who has been receiving propylthiouracil treatment for toxic multinodular goiter since 10 years was admitted to our hospital to be operated because of persisting complaints. The patient was hospitalized for sutureless thyroidectomy after he became euthyroid. Preoperative fiberoptic laryngoscopy performed by the ear, nose, and throat department revealed bilaterally motile vocal folds and a completely open airway. Patient underwent sutureless total thyroidectomy with a vessel sealing device (Ligasure^TM LF1212, Covidien, CO), and a minivac drainage system was placed in the thyroid lodge. On the morning of the first postoperative day, 50 mL of serosanguinous fluid was drained. The patient's voice was normal, and there was no ecchymosis. Postoperative fiberoptic laryngoscopy revealed a hematoma near the right vocal fold and paralysis of the right vocal fold; however, the airway was open. It should be kept in mind that VCP is not solely due to surgery but can also result from intubation, as observed in this case.

Effect of injection augmentation on need for framework surgery in unilateral vocal fold paralysis

OBJECTIVES/HYPOTHESIS

To determine whether injection augmentation reduces the likelihood of ultimately needing definitive framework surgery in unilateral vocal fold paralysis (UVFP) patients.

STUDY DESIGN

Retrospective cohort study.

METHODS

All patients diagnosed with UVFP (2008-2012) at the academic center were identified. The time from symptom onset to presentation to either community otolaryngologist and/or academic center, as well as any directed treatment(s), were recorded. Stepwise, multivariate logistic regression analysis was used to determine whether injection augmentation independently affected odds of needing definitive, framework surgery among patients who were seen within 9 months of symptom onset and had not undergone any prior rehabilitative procedures.

RESULTS

Cohort consisted of 633 patients (55% female, 80% Caucasian, median age 60 years) with UVFP. The majority of etiologies were either surgery (48%) or idiopathic (37%). Duration to presentation at community otolaryngologist was shorter than to the academic center (median 2 vs. 6 months). Overall, less than half of UVFP patients had any operation (46%). Multivariate logistic regression found that earlier injection augmentation did not affect odds of ultimately undergoing framework surgery (odds ratio 1.13; confidence interval, 0.92-1.40; P = 0.23).

CONCLUSION

Nearly half of UVFP patients do not require any rehabilitative procedure. When indicated, early injection augmentation is effective at temporarily alleviating associated symptoms but does not reduce likelihood of needing a definitive framework operation in patients with UVFP. Understanding practice patterns and fostering early detection and treatment may improve quality of life in this patient population.

Laryngeal adductor function in experimental models of recurrent laryngeal nerve injury

OBJECTIVES/HYPOTHESIS

Most patients with unilateral vocal fold paralysis experience some degree of spontaneous reinnervation, which depends upon the type and severity of recurrent laryngeal nerve (RLN) injury. After partial recovery, the paretic vocal fold may or may not adduct adequately to allow glottic closure, which in turn affects phonatory and swallowing outcomes. This process was studied in a series of canine laryngeal nerve injury models.

STUDY DESIGN

Animal (canine) experiments.

METHODS

Maximum stimulable laryngeal adductor pressure (LAP) was measured pretreatment (baseline) and at 6 months following experimental RLN injuries (total n = 59). The nine study groups were designed to simulate a range of severities of RLN injury.

RESULTS

The greatest LAP recovery, at 108% of original baseline, was seen in a 50% transection model; the least recovery was seen when the RLN underwent complete transection with repair, at 56% with precise alignment and 50% with alignment reversed. Intermediate models (partial RLN injuries) gave intermediate results. Crush models recovered 105% of LAP, whereas a half-transection, half-crush injury recovered 72%, and cautery injuries recovered 61%. Controls (complete transection without repair) had no measurable recovery.

CONCLUSIONS

The injured RLN has a strong tendency to recover. Restoration of adductor strength, as determined by the LAP, was predictably related to the severity of RLN injury. The model RLN injuries studied provide a range of expected outcomes that can be used for future experiments exploring interventions that may improve postinjury adductor function.

LEVEL OF EVIDENCE

NA.

A computational study of the role of the aortic arch in idiopathic unilateral vocal-fold paralysis

Unilateral vocal-fold paralysis (UVP) occurs when one of the vocal folds becomes paralyzed due to damage to the recurrent laryngeal nerve (RLN). Individuals with UVP experience problems with speaking, swallowing, and breathing. Nearly two-thirds of all cases of UVP is associated with impaired function of the left RLN, which branches from the vagus nerve within the thoracic cavity and loops around the aorta before ascending to the larynx within the neck. We hypothesize that this path predisposes the left RLN to a supraphysiological, biomechanical environment, contributing to onset of UVP. Specifically, this research focuses on the identification of the contribution of the aorta to onset of left-sided UVP. Important to this goal is determining the relative influence of the material properties of the RLN and the aorta in controlling the biomechanical environment of the RLN. Finite element analysis was used to estimate the stress and strain imposed on the left RLN as a function of the material properties and loading conditions. The peak stress and strain in the RLN were quantified as a function of RLN and aortic material properties and aortic blood pressure using Spearman rank correlation coefficients. The material properties of the aortic arch showed the strongest correlation with peak stress [ρ = -0.63, 95% confidence interval (CI), -1.00 to -0.25] and strain (ρ = -0.62, 95% CI, -0.99 to -0.24) in the RLN. Our results suggest an important role for the aorta in controlling the biomechanical environment of the RLN and potentially in the onset of left-sided UVP that is idiopathic.