Electromyographic investigation of human vocal cord paralysis

Electromyography of the posterior cricoarytenoid muscles: a consensus guideline

PURPOSE

Since the introduction of transcutaneous-transcricoidal needle approaches, electromyography (EMG) of the posterior cricoarytenoid muscle (PCA) became easier to perform and teach. Among the Neurolaryngology working group of the European Laryngological Society, several centers have adopted PCA EMG as part of their routine EMG workup in vocal fold immobility collectively gathering long-term experience. The purpose is to give an update and an extension to already existing guidelines on laryngeal EMG with specific regard to PCA EMG.

METHODS

Consensus of all co-authors is based on continuous exchange of ideas and on joint laryngeal EMG workshop experiences over at least 7 years. A Delphi method of consensus development was used, i.e., the manuscript was circulated among the co-authors until full agreement was achieved.

RESULTS

Step-by-step instructions on how to perform and interpret PCA EMG are provided.

CONCLUSIONS

Further research should include the establishment of normal values for PCA and thyroarytenoid muscle (TA) EMG as well as studies on the nature of some unusual activation pattern commonly seen in chronically lesioned PCA.

Crumley's Classification of Laryngeal Synkinesis: A Comparison of Laryngoscopy and Electromyography

OBJECTIVES/HYPOTHESIS

Applying the principles of misdirected nerve regeneration to the larynx, Roger Crumley in 1989 coined the term laryngeal synkinesis (LS) which he later (2000) classified into 4 types (type I - good voice, type II - involuntary twitches and poor voice, type III - adduction during inspiration, type IV - abduction during phonation). Neurophysiological data were not available for all LS patients at that time. The current study was undertaken to utilize and test the Crumley classification for a clinical interrater comparison and, secondly, compare predicted with actual laryngeal electromyography (LEMG) results.

STUDY DESIGN

Descriptive study.

METHODS

Laryngoscopic and LEMG data of patients with unilateral vocal fold paralysis (VFP) of 6 months duration or longer were combined for retrospective evaluation. Forty-five data sets were available for laryngoscopic classification by two local laryngologists and by Roger Crumley. Twenty-three data sets with complete thyroarytenoid (TA) and posterior cricoarytenoid (PCA) - EMG data were used to compare predicted with actual LEMG results.

RESULTS

Local laryngologists were able to classify 24 of 45, Crumley 30 of 45 cases into one of the 4 synkinesis types. There was substantial agreement between examiners (Cohens Kappa 0.66 [P < .001]). Comparison of predicted and actual LEMG data showed only moderate agreement. EMG sykinesis rates were lower in TA than in PCA and highest in Crumley type I cases.

CONCLUSION

The Crumley classification is helpful in describing and understanding synkinesis. It does not always correlate predictably with actual LEMG data. A complete LEMG mapping of all intrinsic muscles may improve understanding of chronic VFP.

LEVEL OF EVIDENCE

4. Laryngoscope, 131:E1605-E1610, 2021.

PCA Atrophy and Synkinesis as the Main Factors for Persistent Vocal Fold Immobility in RLN Paralysis

OBJECTIVES/HYPOTHESIS

An immobile vocal fold due to recurrent laryngeal nerve (RLN) injury usually shows no gross signs of atrophy and lies near the midline. In 1881, Felix Semon proposed that this phenomenon was due to a selective injury of nerve fibers supplying the posterior cricoarytenoid muscle (PCA) and supported this with postmortem proof of selective PCA atrophy. In recent decades, evidence has emerged that the RLN regenerates after injury but does not always result in useful motion of the vocal folds. It has been proposed that this is caused by laryngeal synkinesis. Laryngeal synkinesis describes a random distribution of regenerated nerve fibers to opposing vocal fold muscles. This study was conducted to clarify the relative contribution of these two potential pathomechanisms in our patient population.

STUDY DESIGN

Retrospective case analysis.

METHODS

Retrospective analysis of laryngeal EMG results from cases with RLN paralysis of at least 6 months duration seen at our neurolaryngology clinic.

RESULTS

Out of 118 PCA EMGs, there was not a single normal or near-normal tracing, whilst 33.3% of TA EMGs indicated normal or near normal innervation. PCA EMGs showed signs of persistent high-grade partial denervation (41.5%) as a sign of atrophy, moderate or strong synkinesis (21.2%), or a combination of both (37.3%).

CONCLUSIONS

In chronic RLN paralysis the intrinsic laryngeal muscles are affected to different extents either by atrophy or synkinesis or a combination of both. The PCA is always affected. The lesser damage to TA innervation explains the commonly seen maintenance of vocal fold muscle bulk.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:E1244-E1248, 2021.

Implications of Synkinesis in Unilateral Vocal Fold Paralysis

Objectives

In patients with unilateral vocal fold paralysis (UVFP), laryngeal electromyography (LEMG) occasionally observes synkinesis in laryngeal muscles, a condition that could impair vocal fold mobility and voice control. This study aims to evaluate the impact of synkinesis on UVFP patients.

Study Design

A retrospective case-control study.

Setting

Medical center.

Subjects and Methods

Patients with UVFP onset >6 months were recruited (N = 104). The outcome measurements included LEMG, quantitative LEMG analysis of thyroarytenoid–lateral cricoarytenoid (TA-LCA) muscle complex, glottal gap measured by videolaryngostroboscopy, voice-related quality of life, and voice acoustic analysis.

Results

According to the LEMG analysis, 8 patients (8%) had synkinesis, and 96 (92%) did not. In the synkinesis group, TA-LCA turn frequency in the lesioned side was comparable to that in the healthy side ( P = .52). Patients in the synkinesis group had higher TA-LCA turn frequency ( P = .001), higher probability of cricothyroid muscle dysfunction ( P = .04), and better voice-related quality of life ( P = .01) but objective voice outcomes comparable to those in the nonsynkinesis group.

Conclusions

Patients with synkinesis will have near-complete restoration in TA-LCA turn frequency but still experience voice impairment, a finding that is compatible with the mechanism of aberrant reinnervation. However, patients with synkinesis have better disease-related quality of life than do those without synkinesis.

Practice Parameter: Laryngeal Electromyography (An Evidence-Based Review)

This paper reports on an evidence-based review of laryngeal electromyography (EMG) as a technique for use in the diagnosis, prognosis, and treatment of laryngeal movement disorders including the laryngeal dystonias, vocal fold paralysis, and other neurolaryngological disorders. The authors performed a systematic review of the medical literature from 1944 through 2001 on the clinical application of EMG to laryngeal disorders. The review yielded 584 articles of which 33 met the predefined inclusion criteria. The evidence demonstrated that in a double-blind treatment trial of botulinum toxin versus saline, laryngeal EMG used to guide injections into the thyroarytenoid muscle in persons with adductor spasmodic dysphonia was beneficial. A cross-over comparison between laryngeal EMG-guided injection and endoscopic injection of botulinum toxin into the posterior cricoarytenoid muscle in abductor spasmodic dysphonia found no significant difference between the 2 techniques and no significant treatment benefit. Based on the evidence, laryngeal EMG is possibly useful for the injection of botulinum toxin into the thyroarytenoid muscle in the treatment of adductor spasmodic dysphonia. There were no evidence-based data sufficient to support or refute the value of laryngeal EMG for the other uses investigated, although there is extensive anecdotal literature suggesting that it is useful for each of them. There is an urgent need for evidence-based research addressing other applications in the use of laryngeal EMG for other applications. (Otolaryngol Head Neck Surg 2004;130: 770-9.)

Recurrent laryngeal nerve regeneration using an oriented collagen scaffold containing Schwann cells

OBJECTIVES/HYPOTHESIS

Regeneration of the recurrent laryngeal nerve (RLN), which innervates the intrinsic laryngeal muscles such that they can perform complex functions, is particularly difficult to achieve. Synkinesis after RLN neogenesis leads to uncoordinated movement of laryngeal muscles. Recently, some basic research studies have used cultured Schwann cells (SCs) to repair peripheral nerve injuries. This study aimed to regenerate the RLN using an oriented collagen scaffold containing cultured SCs.

STUDY DESIGN

Preliminary animal experiment.

METHODS

A 10-mm-long autologous canine cervical ansa was harvested. The nerve tissue was scattered and subcultured on oriented collagen sheets in reduced serum medium. After verifying that the smaller cultivated cells with high nucleus-cytoplasm ratios were SCs, collagen sheets with longitudinally oriented cells were rolled and inserted into a 20-mm collagen conduit. The fabricated scaffolds containing SCs were autotransplanted to a 20-mm deficient RLN, and vocal fold movements and histological characteristics were observed.

RESULTS

Scaffolds containing cultured SCs were successfully fabricated. Immunocytochemical examination revealed that these isolated and cultured cells, identified as SCs, expressed S-100 protein and GFAP but not vimentin. The orientation of SCs matched that of the oriented collagen sheet. Two months after successful transplantation, laryngeal endoscopy revealed coordinated movement of the bilateral vocal folds by external stimulation under light general anesthesia. Hematoxylin and eosin staining showed that the regenerated RLN lacked epineurium surrounding the nerve fibers and was interspersed with collagen fibers. Myelin protein zero was expressed around many axons.

CONCLUSIONS

Partial regeneration of RLN was achieved through the use of oriented collagen scaffolding.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:1622-1627, 2017.

Laryngeal muscle activity in unilateral vocal fold paralysis patients using electromyography and coronal reconstructed images

OBJECTIVE

To assess laryngeal muscle activity in unilateral vocal fold paralysis (UVFP) patients using laryngeal electromyography (LEMG) and coronal images.

STUDY DESIGN

Case series with chart review.

SETTING

University hospital.

SUBJECTS AND METHODS

Twenty-one patients diagnosed with UVFP of at least 6 months in duration with paralytic dysphonia, underwent LEMG, phonatory function tests, and coronal imaging. A 4-point scale was used to grade motor unit (MU) recruitment: absent = 4+, greatly decreased = 3+, moderately decreased = 2+, and mildly decreased = 1+. Maximum phonation time (MPT) and mean flow rate (MFR) were employed. Coronal images were assessed for differences in thickness and vertical position of the vocal folds during phonation and inhalation.

RESULTS

MU recruitment in thyroarytenoid/lateral cricoarytenoid (TA/LCA) muscle complex results were 1+ for 4 patients, 2+ for 5, 3+ for 6, and 4+ for 6. MPT was positively correlated with MU recruitment. Thinning of the affected fold was evident during phonation in 19 of the 21 subjects. The affected fold was at an equal level with the healthy fold in all 9 subjects with MU recruitment of 1+ and 2+. Eleven of 12 subjects with MU recruitments of 3+ and 4+ showed the affected fold at a higher level than the healthy fold. There was a significant difference between MU recruitment and the vertical position of the affected fold.

CONCLUSIONS

Synkinetic reinnervation may occur in some cases with UVFP. MU recruitments of TA/LCA muscle complex in UVFP patients may be related to phonatory function and the vertical position of the affected fold.

Spontaneous laryngeal reinnervation following chronic recurrent laryngeal nerve injury

OBJECTIVES/HYPOTHESIS

To enhance understanding of spontaneous laryngeal muscle reinnervation following severe recurrent laryngeal nerve injury by testing the hypotheses that 1) nerve fibers responsible for thyroarytenoid muscle reinnervation can originate from multiple sources and 2) superior laryngeal nerve is a source of reinnervation.

STUDY DESIGN

Prospective, controlled, animal model.

METHODS

A combination of retrograde neuronal labeling techniques, immunohistochemistry, electromyography, and sequential observations of vocal fold mobility were employed in rat model of chronic recurrent laryngeal nerve injury. The current study details an initial set of experiments in sham surgical and denervated group animals and a subsequent set of experiments in a denervated group.

RESULTS

At 3 months after recurrent laryngeal nerve resection, retrograde brainstem neuronal labeling identified cells in the characteristic superior laryngeal nerve cell body location as well as cells in a novel caudal location. Regrowth of neuron fibers across the site of previous recurrent laryngeal nerve resection was seen in 87% of examined animals in the denervated group. Electromyographic data support innervation by both the superior and recurrent laryngeal nerves following chronic recurrent laryngeal nerve injury.

CONCLUSIONS

Following chronic recurrent laryngeal nerve injury in the rat, laryngeal innervation is demonstrated through the superior laryngeal nerve from cells both within and outside of the normal cluster of cells that supply the superior laryngeal nerve. The recurrent laryngeal nerve regenerates across a surgically created gap, but functional significance of regenerated nerve fibers is unclear.

Laryngeal electromyography in dysphonic patients with incomplete glottic closure

The lack of specificity in laryngoscopical examination requires that the diagnosis of superior laryngeal and recurrent laryngeal nerve involvement be carried out with the aid of electromyography.

Objective

This study aims to assess the electrophysiological function of the superior and inferior laryngeal nerves by measuring the electrical activity of the muscles they innervate in dysphonic patients with incomplete closure of the vocal folds during phonation.

Method

Thirty-nine patients with incomplete glottic closure were enrolled in a prospective study and had their cricothyroid, thyroarytenoid, and lateral cricoarytenoid muscles examined bilaterally through electromyography. Insertion activity, electrical activity at rest (fibrillation, positive wave and fasciculation) and during muscle voluntary contraction (recruitment, amplitude, potential length and latency between electrical activity and phonation) were measured.

Results

No altered test results were observed for parameters insertion activity and electrical activity at rest. None of the patients had recruitment dysfunction. The mean electrical potential amplitude values were within normal range for the tested muscles, as were potential durations and latency times between the onset of electrical activity and phonation.

Conclusion

No signs of denervation were seen in the thyroarytenoid, cricothyroid, and lateral cricoarytenoid muscles of the studied patients.

Recurrent Laryngeal Nerve Regeneration through a Silicone Tube Produces Reinnervation without Vocal Fold Mobility in Rats

Objectives:

We established an animal model of recurrent laryngeal nerve reinnervation with persistent vocal fold immobility following recurrent laryngeal nerve injury.

Methods:

In 36 rats, the left recurrent laryngeal nerve was transected and the stumps were abutted in a silicone tube with a 1-mm interspace, facilitating regeneration. The mobility of the vocal folds was examined endoscopically 5, 10, and 15 weeks later. Electromyography of the thyroarytenoid muscle was performed. Reinnervation was assessed by means of a quantitative immunohistologic evaluation with anti-neurofilament antibody in the nerve both proximal and distal to the silicone tube. The atrophy of the thyroarytenoid muscle was assessed histologically.

Results:

We observed that all animals had a fixed left vocal fold throughout the study. The average neurofilament expression in the nerve both distal and proximal to the silicone tube, the muscle area, and the amplitude of the compound muscle action potential recorded from the thyroarytenoid muscle on the treated side increased significantly (p < 0.05) over time, demonstrating regeneration through the silicone tube.

Conclusions:

Recurrent laryngeal nerve regeneration through a silicone tube produced reinnervation without vocal fold mobility in rats. The efficacy of new laryngeal reinnervation treatments can be assessed with this model.

Short-term laryngeal electromyography and histopathological findings after primary reconstruction of the inferior laryngeal nerve in rabbits: prospective study

INTRODUCTION

The recurrent laryngeal nerve can be injured during surgery. This study investigated recurrent laryngeal nerve reinnervation.

OBJECTIVE

To study the short-term effects of primary anastomosis of the recurrent laryngeal nerve, by laryngeal electromyography and histopathological analysis, in a rabbit model.

METHOD

Twenty Zealand rabbits underwent either right recurrent laryngeal nerve (1) transection with excision of 1 cm or (2) transection and end-to-end primary anastomosis. Vocal fold movements, laryngeal electromyography results and histological changes were recorded.

RESULTS

Vocal fold analysis showed a paramedian vocal fold in both groups, with perceptible vibratory movements in group two. Electromyography revealed total denervation potentials in group one, but denervation and regeneration signs in group two. Histopathologically, hyperkeratosis and parakeratosis of the vocal fold mucosa were seen in group one, and signs of parakeratosis and hyperplasia in group two.

CONCLUSION

Even under ideal conditions for primary recurrent laryngeal nerve anastomosis, a return to normal muscle function is unlikely. However, such anastomosis prevents muscle atrophy, and should be performed as soon as possible. The degree of nerve recovery is associated with the number, amplitude and myelination level of fibrils returning to the original motor end-plaque.

Laryngeal reinnervation surgery - results of a selective approach in an animal study

Laryngeal reinnervation surgery is a difficult subject due to the fact that the recurrent laryngeal nerve (RLN) is responsible for both adductor and abductor laryngeal activity. Non-selective reinnervation procedures will result in laryngeal synkinesis with restoration of tonicity. Restoration of mobility requires selective reinnervation of the adductor and abductor branches with nerves with similar activity patterns as the initial abductor and adductor branches of the RLN.

Unilateral true vocal fold synkinesis presenting with airway obstruction

OBJECTIVES

We present a case series of 10 patients with unilateral true vocal fold paralysis who presented with airway obstruction.

METHODS

A retrospective review of the authors' patients at 2 institutions with unilateral true vocal fold motion impairment was carried out over a 10-year period. Of these, 10 patients were identified who presented with stridor and dyspnea as a result of synkinesis. Six cases were a result of thyroidectomy, 1 case resulted from recurrent laryngeal nerve section for spasmodic dysphonia, 1 case occurred after anterior cervical diskectomy and fusion, and in 2 cases no cause was identified.

RESULTS

Three patients underwent tracheotomy. Two patients underwent partial arytenoidectomy. Seven patients underwent botulinum toxin injection; 2 were treated with breathing therapy, and in 1 case breathing therapy was recommended. Seven patients underwent treatment with more than 1 method.

CONCLUSIONS

Unilateral vocal fold paralysis may present with airway obstruction as a result of synkinesis. Treatment should be incremental and starts with breathing therapy and botulinum toxin injection. Partial arytenoidectomy or tracheotomy may be necessary for refractory cases.

Characterization of arytenoid vertical displacement in unilateral vocal fold paralysis by three-dimensional computed tomography

The paralyzed arytenoid is not immobile and is subjected to passive movement during phonation. If anatomical changes during inspiration and phonation are compared by three-dimensional computed tomography (3D CT), it is possible to observe vertical movement of the paralyzed arytenoid. Our aim was to use 3D CT to examine the characteristics of 3D arytenoid movement in unilateral vocal fold paralysis (UVFP). This is a prospective study. A total of 61 patients (18 females and 43 males) with UVFP who had undergone 3D CT imaging between April 2005 and January 2007 were included. Cricoid and arytenoid cartilage was imaged by 3D CT. We detected the movements of the paralyzed side when comparing inspiration and phonation. The degree of cranial displacement of the paralyzed arytenoids was classified into three grades (I for mild to III for severe). The mean flow rate (MFR) was calculated for each grade. By comparing the MFR of each grade with the normal control group, we determined whether cases would worsen according to grade. Passive gliding movement of the paralyzed arytenoids was found in 90.7% of cases. In all cases, the paralyzed arytenoids were displaced cranially compared to the unaffected side. MFR worsened significantly as the grade became more severe. We believe that the passive gliding movements observed when comparing inspiration and phonation are characteristic of paralysis. Even in mild cases, the paralyzed arytenoids are passively displaced cranially during phonation, and the degree of this displacement is one indicator that can be used to evaluate the severity of UVFP.

The Value of Laryngeal Electromyography in the Evaluation of Laryngeal Motion Abnormalities

SUMMARY

Laryngeal electromyography (EMG) functions routinely as a prognostic tool in the evaluation of vocal fold paralysis, as a guide for therapeutic injections into the laryngeal muscles, and more recently as an assessment tool in the evaluation of vocal fold paresis. This study investigates the clinical utility of laryngeal EMG as a diagnostic aid in the evaluation of movement disorders of the larynx in patients complaining of dysphonia. A retrospective chart review of all laryngeal EMGs performed at a tertiary laryngology referral center over a 13-month period was performed. All laryngeal EMGs were performed to evaluate laryngeal motion abnormalities in dysphonic patients. Thirty-seven laryngeal EMGs were completed during this study period. Analysis of the data revealed that the medical treatment plan changed as a result of findings on laryngeal EMG in 10/37 patients (27.0%); laryngeal EMG guided and/or confirmed the course of treatment in 12/37 patients (32.4%) and did not change the treatment plan in 15/37 patients (40.5%). Laryngeal EMG is a useful diagnostic tool that, in this study, contributed significantly to and helped guide the evaluation and management of motion disorders in the larynx of dysphonic patients.

Mild Vocal Fold Paresis: Understanding Clinical Presentation and Electromyographic Findings

The implications of mild vocal fold hypomobility are incompletely understood. This study describes the clinical, electromyographic, and probable etiologic findings in patients who presented with complaints of dysphonia and whose physical examination revealed vocal fold paresis as a factor possibly contributing to their voice complaints. A retrospective chart review of all patients who presented to a tertiary laryngology referral center over a 13-month period, who had a clinical diagnosis of mild vocal fold hypomobility and who underwent laryngeal electromyography, were included in the study. A total of 22 patients completed the medical evaluation of their voice complaint. Of these patients, 19 (86.4%) were found to have evidence of neuropathy on laryngeal electromyography. The clinical picture indicated the following probable origins for the vocal fold paresis: goiter/thyroiditis (7/22 or 31.8%), idiopathic (4/22 or 18.2%), viral neuritis (4/22 or 18.2%), trauma (3/22 or 13.6%), and Lyme's disease (1/22 or 4.5%). This article describes the clinical entity of mild vocal fold hypomobility and associated flexible laryngoscopic, rigid strobovideolaryngoscopic, and laryngeal electromyographic findings.

A new electromyographic definition of laryngeal synkinesis

Laryngeal synkinesis involves the misdirected reinnervation of an injured recurrent laryngeal nerve to vocal fold abductor and adductor musculature. The resultant laryngeal dyscoordination can cause vocal fold immobility and airway compromise. Although this entity is sometimes considered in the differential diagnosis, it is only demonstrable with laryngeal electromyography (EMG). We propose a new EMG definition of synkinesis to assist in its identification during workup of vocal fold immobility. A retrospective chart review from 1992 to 1997 in the Voice Disorders Clinic identified 10 patients with laryngeal synkinesis. Five patients had bilateral immobility, and 5 had unilateral immobility. Monopolar EMG was performed on all patients. Fine-wire EMG was performed when monopolar EMG did not elucidate the cause of the immobility. The EMG studies revealed synkinetic reinnervation in all subjects. On the basis of the EMG results, 7 of the 10 patients were treated with botulinum toxin to weaken the undesired reinnervation. Three of the 7 patients had benefit from this therapy. Laryngeal synkinesis should be considered as part of the differential diagnosis of vocal fold immobility. Awake laryngeal EMG is the only method to demonstrate synkinesis of the larynx. The diagnosis of synkinesis is clinically significant in cases of immobility to identify patients who might benefit from botulinum toxin therapy. Additionally, the presence of synkinesis in cases of unilateral immobility may be a contraindication to laryngeal reinnervation procedures. The benefit of botulinum toxin therapy is likely greater in the treatment of bilateral as opposed to unilateral immobility.

Electromyography and the immobile vocal fold

Laryngeal EMG has become a useful tool for the otolaryngologist in the four decades since the pioneering work of Faaborg-Anderson and Buchtal. It is able to distinguish between mechanical limitation and denervation in an immobile vocal fold. In the paralyzed vocal fold, it can guide workup by pointing to the site of the lesion. In the hands of a circumspect clinician, it can provide clinically valuable information regarding prognosis. Useful application of laryngeal EMG must rest on the basic fact that it isa qualitative test. Because of factors like sampling error, interfering signal from neighboring muscles, difficulties in needle placement, and our in-complete understanding of reinnervation physiology, the boundary between sophisticated, subtle interpretation and overreading is particularly difficult to distinguish. EMG diagnosis is based on patterns of abnormalities over time and, like other tests, requires interpretation in a clinical context. As in any such undertaking, there is no substitute for good judgment and experience. The most important benefit of clinical use of laryngeal EMG may be that it has catalyzed and broadened interest in laryngeal neurophysiology in the same way that stroboscopy has focused attention on the structure and function of the vocal fold lamina propria. The continuing refinement of electrodiagnostic approaches to the larynx that has resulted, including quantitative, single-fiber. and vector laryngeal EMG, and evolving methods of nerve conduction testing will continue to yield important insights into mechanisms of neural control that are likely to drive developments in the treatment of vocal fold paralysis in the future.

Restoring Vocal Fold Movement after Transection and Immediate Suturing of the Recurrent Laryngeal Nerve with Local Application of Basic Fibroblast Growth Factor: An Experimental Study in the Rat

OBJECTIVE

To evaluate the effects of basic fibro-blast growth factor (bFGF) on the recovery of vocal fold movement and the attenuation of laryngeal muscle atrophy after transection of the recurrent laryngeal nerve (RLN).

STUDY DESIGN

Quantitative assessment of vocal fold movement using the video cassette recorder (VCR) image-analysis method and histologic examination of the laryngeal muscle.

METHODS

Fifty-eight Wistar rats underwent RLN transection and one of the following three procedures: 1) transection of the RLN alone (transection group, n = 18), 2) suture of the nerve stumps followed by local administration of phosphate-buffered saline (PBS) solution using an osmotic pump (PBS group, n =20), or 3) suture of the nerve stumps followed by local administration of bFGF (FGF group, n = 20). Vocal fold movements were recorded with VCR by way of a rigid endoscope, and the VCR images were analyzed on a computer. Histologic changes in the thyroarytenoid (TA) muscle were evaluated by measuring the cross-sectional area of the muscle and average size of muscle fibers.

RESULTS

In the transection group, vocal fold movement did not recover, and atrophy of the TA muscle gradually progressed after sectioning the nerve. In contrast, vocal fold movement as assessed by VCR image-analysis recovered in some cases in the immediate suturing groups, more markedly in the FGF group (34.1 +/- 29.1%) than in the PBS group (5.5 +/- 7.9%) (P <.05). Histologically, atrophy of the laryngeal muscle was significantly attenuated by the local administration of bFGF.

CONCLUSION

bFGF facilitates regeneration of the transected RLN and attenuation of intrinsic laryngeal muscle atrophy, thereby restoring laryngeal function.

Recent advances in laryngeal sensorimotor control for voice, speech and swallowing

PURPOSE OF REVIEW

This article reviews advances in knowledge on laryngeal sensorimotor control affecting the assessment, understanding, and treatment of laryngeal motor control disorders in voice, speech, and swallowing. Three topics are covered: new knowledge on laryngeal innervation and central nervous system control from basic research studies, the role of laryngeal sensation in normal swallowing and dysphagia in patients, and new approaches to the restoration of laryngeal motor control after recurrent laryngeal nerve disorders.

RECENT FINDINGS

A significant advance this year was tracing the efferent pathways from the cortex to the brainstem in monkeys. This provided new information on subcortical and brainstem connections in the laryngeal efferent pathways. Laryngeal sensory feedback continued to receive attention, and the role of sensory feedback in the control of the pharyngeal phase of swallowing is now well established. Further developments in neuromotor monitoring of the recurrent laryngeal nerve during thyroidectomy were seen, and a large case series recommended that these techniques become standard practice for surgery for thyroid benign recurrence or malignancy. Finally, the first tissue engineering papers in the field of vocal fold tissue and nerve restoration were published this year, beginning an exciting new approach to restoration of laryngeal motor control.

SUMMARY

Considerable attention has been given to laryngeal muscle physiology, denervation, and sensation in neurolaryngology. Relatively limited understanding is available regarding the central nervous system integrative control of laryngeal function for speech, respiration, and swallowing.

Practice parameter: laryngeal electromyography (an evidence-based review)

This paper reports on an evidence-based review of laryngeal electromyography (EMG) as a technique for use in the diagnosis, prognosis, and treatment of laryngeal movement disorders, including the laryngeal dystonias, vocal fold paralysis, and other neurolaryngological disorders. The authors performed a systematic review of the medical literature from 1944 through 2001 on the clinical application of EMG to laryngeal disorders. Thirty-three of the 584 articles met the predefined inclusion criteria. The evidence demonstrated that in a double-blind treatment trial of botulinum toxin versus saline, laryngeal EMG used to guide injections into the thyroarytenoid muscle in persons with adductor spasmodic dysphonia was beneficial. A cross-over comparison between laryngeal EMG-guided injection and endoscopic injection of botulinum toxin into the posterior cricoarytenoid muscle in abductor spasmodic dysphonia found no significant difference between the two techniques and no significant treatment benefit. Based on the evidence, laryngeal EMG is possibly useful for the injection of botulinum toxin into the thyroarytenoid muscle in the treatment of adductor spasmodic dysphonia. There were no evidence-based data sufficient to support or refute the value of laryngeal EMG for the other uses investigated, although there is extensive anecdotal literature suggesting that it is useful for each of them. There is an urgent need for evidence-based research addressing other applications in the use of laryngeal EMG for other applications.

Neurophysiology of swallowing

Swallowing is a complex motor event that is difficult to investigate in man by neurophysiological experiments. For this reason, the characteristics of the brain stem pathways have been studied in experimental animals. However, the sequential and orderly activation of the swallowing muscles with the monitoring of the laryngeal excursion can be recorded during deglutition. Although influenced by the sensory and cortical inputs, the sequential muscle activation does not alter from the perioral muscles caudally to the cricopharyngeal sphincter muscle. This is one evidence for the existence of the central pattern generator for human swallowing. The brain stem swallowing network includes the nucleus tractus solitarius and nucleus ambiguus with the reticular formation linking synaptically to cranial motoneuron pools bilaterally. Under normal function, the brain stem swallowing network receives descending inputs from the cerebral cortex. The cortex may trigger deglutition and modulate the brain stem sequential activity. The voluntarily initiated pharyngeal swallow involves several cortical and subcortical pathways. The interactions of regions above the brain stem and the brain stem swallowing network is, at present, not fully understood, particularly in humans. Functional neuroimaging methods were recently introduced into the human swallowing research. It has been shown that volitional swallowing is represented in the multiple cortical regions bilaterally but asymmetrically. Cortical organisation of swallowing can be continuously changed by the continual modulatory ascending sensory input with descending motor output.

SIGNIFICANCE

Dysphagia is a severe symptom complex that can be life threatening in a considerable number of patients. Three-fourths of oropharyngeal dysphagia is caused by neurological diseases. Thus, the responsibility of the clinical neurologist and neurophysiologist in the care for the dysphagic patients is twofold. First, we should be more acquainted with the physiology of swallowing and its disorders, in order to care for the dysphagic patients successfully. Second, we need to evaluate the dysphagic problems objectively using practical electromyography methods for the patients' management. Cortical and subcortical functional imaging studies are also important to accumulate more data in order to get more information and in turn to develop new and effective treatment strategies for dysphagic patients.

Laryngeal electromyography: an evidence-based review

This article reports on an evidence-based review of laryngeal electromyography (EMG) as a technique for use in the diagnosis, prognosis, and treatment of laryngeal movement disorders including the laryngeal dystonias, vocal fold paralysis, and other neurolaryngological disorders. The authors performed a systematic review of the medical literature from 1944 through 2001 on the clinical application of EMG to laryngeal disorders. Thirty-three of the 584 articles met the predefined inclusion criteria. The evidence demonstrated that in a double-blind treatment trial of botulinum toxin versus saline, laryngeal EMG used to guide injections into the thyroarytenoid muscle in persons with adductor spasmodic dysphonia was beneficial. A cross-over comparison between laryngeal EMG-guided injection and endoscopic injection of botulinum toxin into the posterior cricoarytenoid muscle in abductor spasmodic dysphonia found no significant difference between the two techniques and no significant treatment benefit. Based on the evidence, laryngeal EMG is possibly useful for the injection of botulinum toxin into the thyroarytenoid muscle in the treatment of adductor spasmodic dysphonia. There were no evidence-based data sufficient to support or refute the value of laryngeal EMG for the other uses investigated, although there is extensive anecdotal literature suggesting that it is useful for each of them. There is an urgent need for evidence-based research addressing the use of laryngeal EMG for other applications.

Visual observations of glottal configuration and vocal outcomes in arytenoid adduction

Arytenoid adduction procedures involve approximation of the arytenoid cartilages with the goal of reducing posterior glottal gap size and improving voice. However, voice outcomes after arytenoid adduction are not always optimal and may be improved by precise use of suture placements, forces, and direction angles. The development of intraoperative methods of assessing optimal suture direction appears critical for achieving the best voice outcome. The goal of this study was to examine the relationship of visual classification of glottal configuration, digital measures of the glottis, acoustic and aerodynamic measures, and voice outcome. Our results suggested that visual classification of glottal configuration was not useful in distinguishing voice outcome, except for cases in which there was a large posterior glottal gap. In contrast, acoustic and aerodynamic measures were related to digitized glottal measures and may be developed into a useful method of intraoperative monitoring.

Utility of laryngeal electromyography in predicting recovery after vocal fold paralysis

OBJECTIVES

To determine the value of laryngeal electromyography in predicting recovery after vocal fold paralysis and to determine what elements of laryngeal electromyography are most predictive of outcome.

DESIGN

Cohort study with retrospective data review.

SETTING

University voice center.

PARTICIPANTS

Consecutive sample of 31 patients with vocal fold paralysis diagnosed by indirect laryngoscopy, using either nasal insertion with a flexible nasopharyngoscope or peroral with a 70 degrees Hopkins rod. Inclusion criteria were that laryngeal electromyography had to have been performed between 21 days and 6 months from the onset of symptoms and patients must have been followed a minimum of 6 months.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Vocal fold motion at 6 months from onset of symptoms.

RESULTS

Nine subjects (29%) had resolved vocal fold motion, whereas 22 (71%) had persistent vocal fold paralysis. By using our laryngeal electromyography paradigm, 4 of 6 patients with a laryngeal electromyography prognosis of excellent resolved. The predictive value for a negative test was 66.7%. For patients with a fair or poor prognosis, 5 of 25 resolved. The predictive value for a positive test was 80%. Only 8 of 22 patients with persistent vocal fold paralysis had fibrillations, and spontaneous activity was not significantly related to outcome. Patients with absent or greatly decreased motor unit recruitment had a significantly higher proportion of permanent vocal fold paralysis (P<.05). Stepwise forward logistic regression determined that prognosis by laryngeal electromyography and onset time were significant predictors of outcome (P<.01). The model predicted 44.4% of resolved cases, which represents a moderate prediction.

CONCLUSIONS

This study confirms the utility of laryngeal electromyography in assessing prognosis for recovery of vocal fold motion after laryngeal nerve injury. The results support our hypothesis that preset decision rules based on laryngeal electromyography data can be effectively used to determine a prognosis for recovery of vocal fold motion.

Recurrent laryngeal nerve regeneration by tissue engineering

The recurrent laryngeal nerve (RLN) does not regenerate well after it has been cut, and no current surgical methods achieve functional regeneration. Here, we evaluate the functional regeneration of the RLN after reconstruction using a biodegradable nerve conduit or an autologous nerve graft. The nerve conduit was made of a polyglycolic acid (PGA) tube coated with collagen. A 10-mm gap in the resected nerve was bridged by a PGA tube in 6 adult beagle dogs (group 1) and by an autologous nerve graft in 3 dogs (group 2). Fiberscopic observation revealed functional regeneration of the RLN in 4 of the 6 dogs in group 1. No regeneration of the RLN was observed in any dog in group 2. We also tested for axonal transport, and measured the compound muscle action potential. The RLN can be functionally regenerated with a PGA tube, which may act as a scaffold for the growth of regenerating axons.

Glottal configuration, acoustic, and aerodynamic changes induced by variation in suture direction in arytenoid adduction procedures

Arytenoid adduction is a phonosurgical procedure in which the arytenoid cartilages are approximated to reduce posterior glottal gap size and improve voice. Voice outcomes following arytenoid adduction are not always optimal. The goal of this study was to systematically vary suture direction and force of pull on the arytenoid cartilages in a human excised laryngeal model to determine the optimal combination of factors for reducing glottal gap and improving voice. Several factors demonstrated significant effects. Changes in suture direction and force of pull affected glottal configuration in both the horizontal and vertical planes. Increased force of pull on the muscular process resulted in increased adduction of the vocal process for all suture directions. Changes in suture direction and force of pull also affected acoustic and aerodynamic measures of induced voice. Therefore, voice outcomes can be optimized with arytenoid adduction if the vocal fold plane is accurately adjusted.

Thyroarytenoid muscle maintains normal contractile force in chronic vocal fold immobility

BACKGROUND

Denervation of skeletal muscle typically results in irreversible denervation atrophy over time. This finding has generated controversy as to the efficacy of reinnervation procedures for chronic vocal fold immobility related to recurrent laryngeal nerve injury.

OBJECTIVE

To test the hypothesis that chronic vocal fold immobility after recurrent laryngeal nerve injury does not result in diminished maximal isometric force generation in the thyroarytenoid muscle.

STUDY DESIGN

Adult random-bred cats underwent either unilateral laryngeal denervation (n = 6) or sham surgery (n = 6). After 6 months, videolaryngoscopy was performed followed by in vitro measurement of maximal isometric tetanic force produced by the thyroarytenoid muscle.

RESULTS

All animals in the denervation group showed right vocal fold paralysis after the initial denervation operation; none of these animals had return of appropriately phased movement with respiration. Four had intermittent disorganized twitching movements. One had these movements plus an occasional weak adduction, and one had no movement. Normal vocal fold mobility was observed in 6 of 6 animals undergoing sham surgery. The maximal isometric tetanic force measured from the thyroarytenoid muscle in the sham group was 438 mN (+/-92 mN standard deviation [SD]). The maximal isometric tetanic force measured from the thyroarytenoid muscle in the chronically immobile group was 405 mN (+/-107 mN SD). Differences were not statistically significant.

CONCLUSION

Maximal isometric force in the thyroarytenoid muscle is not diminished in chronic vocal fold immobility after recurrent laryngeal nerve injury. We conclude that the possibility for restoration of contractile force to the chronically immobile thyroarytenoid muscle exists. This finding supports the pursuit of reinnervation procedures in the treatment of chronic vocal fold immobility.

The electromyographic behavior of the thyroarytenoid muscle during swallowing

The electromyographic (EMG) behavior of the laryngeal adductors (e.g., the thyroarytenoid [TA] muscle) during swallowing has been scarcely studied. However, the detailed analysis of TA muscle is important to understand the physiology of swallowing. We investigated 14 healthy adult subjects. Activation of the TA laryngeal adductor muscle was compared with the mechanically measured laryngeal up-down movement and with the onset of excitation of laryngeal elevators, such as submental (SM) muscles, during swallowing. The laryngeal adductor of TA and laryngeal elevators of SM muscles were electromyographically (integrated/rectified) recorded. The vertical laryngeal movements during swallowing were recorded using a piezoelectric sensor. The EMG behavior of the TA muscle revealed three different activities during swallowing. The basic activity was stable; it almost started with the upward movement of larynx and after the SM-EMG onset. A fore-burst was recorded just before the upward movement of the larynx and a late-burst appeared just after the downward movement. The fore-burst was proposed to be related with oral-laryngeal reflexes, and the late-burst could be a rebound activity after a short expiration of swallowing, while the basic activity is accepted to be a part of activity of central-pattern generator of swallowing program.

Motor innervation of the guinea pig interarytenoid muscle: reinnervation process following unilateral denervation

The authors investigated the process of denervation and reinnervation of the interarytenoid (IA) muscle in the guinea pig using transmission electron microscopy and glycogen depletion technique after unilateral transection of the recurrent laryngeal nerve (RLN) and superior laryngeal nerve to clarify the innervation pattern of the unpaired IA muscle. Anastomosis between the bilateral arytenoid branches was confirmed in the belly of the IA muscle. Five weeks after transection, all of the IA muscle fibers appeared to have been reinnervated by the contralateral RLN. As the arytenoid branch of the RLN runs together with that of the contralateral RLN in a single intramuscular nerve funiculus, it is possible that collateral sprouting branches grow and extend into the adjacent denervated Schwann's sheaths. The authors conclude that the unpaired IA muscle, as a whole, receives specific motor nerve supply from the bilateral RLNs, although each muscle fiber is innervated unilaterally.

Changes in length and spatial orientation of the vocal fold with arytenoid adduction in cadaver larynges

Videoendoscopy suggests that arytenoid adduction (AA) surgery not only medializes the paralyzed vocal fold, but increases the length of its membranous portion so that it more closely resembles the normal side. This could represent either real length change or out-of-plane rotation. Computed tomography scanning was performed on adult male cadaver larynges before and after the AA procedure to measure changes in length and spatial orientation of the vocal fold. Three-dimensional coordinates of radiopaque markers on the anterior commissure, posterior glottic midline, and vocal processes were determined. The distance between the vocal processes was 3.9 mm before, and 0.8 mm after AA. The mean vocal fold length was 12.4 mm before, and 13.4 mm after AA (p = .14). The vocal process moved consistently caudally, an average of 3.5 mm (p = .02). The data suggest that clinically apparent vocal fold length changes with AA could be an illusion due to vertical displacement of the vocal process, and not actual lengthening.

Major patterns of laryngeal electromyography and their clinical application

Laryngeal electromyography (LEMG) is clinically valuable in the evaluation of laryngeal dysfunction and vocal fold immobility. To facilitate clinical application of this electrophysiologic test, a detailed description of modified LEMG techniques is presented. The techniques were applied for simultaneous bilateral recordings of the thyroarytenoid, cricothyroid, and posterior cricoarytenoid muscles. The basic patterns of LEMG are classified into three different types: normal, neuropathy, and myopathy. In an attempt to characterize these patterns, we have reported eight LEMG-documented cases: unilateral laryngeal paralysis, bilateral laryngeal paralysis, cricoarytenoid joint dislocation, cricoarytenoid joint ankylosis, laryngeal myopathy, pharyngeal paralysis (soft palate paralysis), spasmodic dysphonia, and unilateral laryngeal paralysis with anastomosis. The significance of the major LEMG patterns is discussed.

Semon's law revisited: an electromyographic analysis of laryngeal synkinesis

Felix Semon's fascination with vocal fold paralysis led to his theory attributing medialization to isolated abductor paralysis. Later, the Wagner-Grossman hypothesis explained the vocal fold position on the basis of cricothyroid muscle activity. Other authors since that time have dispelled the notion of a role for the cricothyroid muscle in vocal fold position with paralysis. Utilizing laryngeal electromyography, several authors have found electrical activity suggestive of variable reinnervation and synkinesis. This current study included patients with persistent vocal fold immobility. Fourteen patients were studied: half with good voice and half with poor voice. The patients with good voice had a relatively normal arytenoid position and evidence of synkinesis. The group with poor voice had an arytenoid that tipped into the laryngeal inlet and had denervation or poor reinnervation. This suggests that the medialization and upright position of the arytenoid is due to synkinesis.

Laryngeal neurophysiology and its clinical uses

A fact well known to all otolaryngologists, but which occasionally bears repeating, is that the larynx is not just an organ of communication. The larynx sits at the crossroads of the pathways of air and food intake, and serves the vital function of keeping ingested food and water from entering the lungs. Another obvious consideration, however, is that if the larynx were not there and if the breathing and alimentary passages were totally separate (as after surgical laryngectomy), then there would be no need for the larynx other than to speak. Thus, in terms of survival of the organism, laryngectomy can be considered a viable treatment option any time laryngeal dysfunction compromises health. The problem with this line of reasoning, of course, is that speech, in humanistic terms, is a very compelling need. Someone who communicates in any mode other than that of normal speech is at a distinct disadvantage in almost any culture. Therefore, at its essence, the subspecialty of laryngology has as its central mission the preservation or restoration of normal voice and speech by the natural mechanism. In accomplishing this, it is necessary to understand how the larynx functions as an integral component of the systems for speech, breathing, and swallowing. The intent of this article is to outline essential features of laryngeal function, to describe how function is impaired by diseases, and to offer examples of the clinical significance of this information.

[Presymptomatic injury of the recurrent laryngeal nerve in benign thyroid disease: contribution of electromyography]

Diagnosis of recurrent laryngeal nerve palsy is usually possible through a clinical, laryngoscopical and electromyographical approach, but at a critical stage of the nerve injury. We observed four cases of benign thyroïd tumoral processes with a preoperative electromyographic examination showing neurogenic abnormalities in the thyroarytenoid muscle without any clinical symptoms. We presume that only laryngeal electromyography permits the diagnosis of mild, even asymptomatic laryngeal recurrent nerve injury. A recurrent laryngeal nerve palsy occurs in thyroid tumors, most often in malignant conditions, rarely in benign ones. Nevertheless early forms of nerve injury with benign thyroïd pathology could be underrated. Since the functional prognosis of symptomatic laryngeal nerve palsy is doubtful, laryngeal electromyography, through its ability to diagnose early nerve injury, provides helpful indications in thyroïd benign tumoral diseases for the therapeutic decision.

A preliminary study of the prognostic role of electromyography in laryngeal paralysis

Confidence in the reliability of laryngeal electromyography to predict recovery is critical if this tool is to be used to select the type and timing of surgical intervention. The characteristics of electromyography of 14 patients with unilateral vocal fold paralysis were assessed to determine which factor or combination of factors would be most useful in determining prognosis. We examined the duration, amplitude, waveform morphology, root-mean-square, and time interval from onset to electromyography recording. The results supported the concept that electromyography recordings are valuable in determining prognosis if performed before 6 months and preferably within 6 weeks of onset of laryngeal paralysis. A positive prognosis for laryngeal recovery was indicated when the following electromyography features were present in the immobile vocal fold: (1) normal motor unit waveform morphology, (2) overall electromyography activity characterized by a root-mean-square value greater than 40 microV in any one task, and (3) no electrical silence during voluntary tasks. On the basis of this criteria our overall correct prognostic rate was 89%.

Quantitative analysis of EMG interference pattern in patients with laryngeal paresis

Conventional (visual) analysis of EMG was compared to a computerized quantitative method (turns/amplitude). Ten patients with a clinical history of peripheral nerve lesion were examined in order to investigate whether quantitative analysis of EMG increased the diagnostic sensitivity of peripheral nerve lesions to the laryngeal muscles. Quantitative analysis either agreed with conventional analysis or resulted in false negative diagnosis compared to conventional analysis. Thus, conventional analysis turned out to be more sensitive to neurogenic damage than the quantitative method. EMG results were compared to clinical findings.

Correlation between stroboscopy and electromyography in laryngeal paralysis

Twenty patients with vocal fold motion impairment were reviewed to correlate the findings of electromyography (EMG) and stroboscopy. The causes of motion impairment were idiopathic, previous surgery with recurrent laryngeal nerve injury, neck and skull base trauma, and neoplasm. The EMG studies were analyzed to assess the status of innervation of the immobile vocal fold. The presence or absence of the mucosal wave prior to therapeutic intervention was determined with stroboscopic examination. Eight of 10 patients with EMG evidence of reinnervation or partial denervation were found to have mucosal waves, and 3 of 10 patients with EMG evidence of denervation were found to have mucosal waves. Six patients developed mucosal waves after surgical medialization, despite evidence of denervation by EMG criteria. These findings support the premise that tension and subglottic pressure, rather than status of innervation, determine the presence of the mucosal wave.

Vocal cord paralysis: clinical and electrophysiologic features

Vocal cord paralysis may occur in isolation or as part of a constellation of findings in neurological disease. We investigated the pathophysiology of these disorders with laryngeal electromyography (LEMG). We studied 44 patients with idiopathic vocal cord paralysis, confirmed by laryngoscopy. The major LEMG finding, present in 29 vocal cords, was evidence of active or chronic denervation in the thyroarytenoid (TA), indicating recurrent laryngeal neuropathy. Denervation of the cricothyroid (CT) in 5 patients indicated superior laryngeal neuropathy. TA and CT involvement in 1 patient indicated proximal laryngeal or vagus nerve damage. LEMG was performed in 48 patients with other laryngeal disorders. LEMG proved to be a safe and effective procedure in the diagnosis of laryngeal neuropathy as distinguished from supranuclear and mechanical disorders of the larynx.

Bipolar hooked-wire electromyographic technique in the evaluation of pediatric vocal cord paralysis

Laryngeal electromyography is a valuable test to assess vocal cord paralysis in adults. This technique can be applied and adapted to the pediatric patient. In the operating room under general anesthesia and endoscopic guidance, bipolar hooked-wire electrodes are passed percutaneously through the anterior neck skin into both thyroarytenoid muscles. Electromyographic signals are evaluated during light anesthesia and on awakening. A critical appraisal of this technique is presented, including an analysis of sources of electrical interference in the operating room.

The clinical differentiation between vocal cord paralysis and vocal cord fixation using electromyography

With newer techniques for laryngeal intervention, it becomes a practical necessity to understand whether an immobile cord is due to neurogenic dysfunction or cricoarytenoid fixation. An objective test for this differentiation is laryngeal electromyography, which can be done as an office procedure with a minimum of discomfort. Our experience in a clinical setting has shown laryngeal electromyography to be efficient in accurately assessing the neuromuscular status of the intrinsic laryngeal musculature.

Misdirected reinnervation in the feline intrinsic laryngeal muscles after long-term denervation

Nerve terminals which resembled the autonomic nerve varicosities were found at all neuromuscular junctions of the feline intrinsic laryngeal muscles after 21 months of unilateral laryngeal paralysis. The structure of muscle fibers was preserved throughout this period, although there was no evidence of regeneration of transected recurrent laryngeal nerve. In the cricothyroid muscle, misdirected reinnervation was recognized in the different pathways from the other intrinsic laryngeal muscles.

Intraoperative laryngeal electromyographic assessment of patients with immobile vocal fold

The differential diagnosis of laryngeal ankylosis versus paralysis is occasionally difficult in patients with immobile vocal folds. Eight patients with acute and chronic evidence of vocal fold immobility were investigated by intraoperative electromyography (IEMG) during planned microlaryngoscopy. Bipolar hook wire electrodes were inserted into the thyroarytenoid muscle, of which the electrical activity was monitored during neuromotor blockade and emergence from anesthesia. The normal side and the side with ankylosis or stenosis showed normal IEMG activity. There was progressive recruitment of larger motor units during recovery from muscle relaxation. Patients with laryngeal paralysis failed to show such recruitment patterns. Thus, IEMG can be used as a diagnostic tool during operative laryngoscopy to differentiate neuromotor injury from anatomic causes of vocal fold immobility. The advantages of IEMG are its ease of application and certainty of electrode position. It can also be used to monitor recurrent nerve integrity and detect early laryngospasm. Further IEMG clinical study is warranted.

Evaluation of laryngeal muscle function by quantitative analysis of the EMG interference pattern

A computerized method for quantitative analysis of the EMG interference pattern was tested in the cricothyroid and thyroarytenoid muscles with the purpose of evaluating its usefulness for clinical purposes. In a normal male subject the mean amplitude and the number of turns/s were extracted from the EMG signal of sustained chest register phonations, with systematic variation of vocal pitch and intensity. In the cricothyroid, as well as the thyroarytenoid muscle, there was a considerable increase in mean amplitude and turns/s with both increased pitch and increased intensity. Pitch variation was the most effective way to induce changes in turns and amplitude levels in both muscles. In contrast to results from studies of larger muscles, the increase in both amplitude and turns was proportional to muscle force also at the highest loads.