Nerve-Muscle Pedicle Reinnervation of the Paralyzed Vocal Cord

Partial recovery of respiratory function and diaphragm reinnervation following unilateral vagus nerve to phrenic nerve anastomosis in rabbits

Respiratory dysfunction is the leading cause of mortality following upper cervical spinal cord injury (SCI). Reinnervation of the paralyzed diaphragm via an anastomosis between phrenic nerve and a donor nerve is a potential strategy to mitigate ventilatory deficits. In this study, anastomosis of vagus nerve (VN) to phrenic nerve (PN) in rabbits was performed to assess the potential capacity of the VN to compensate for lost PN inputs. At first, we compared spontaneous discharge pattern, nerve thickness and number of motor fibers between these nerves. The PN exhibited a highly rhythmic discharge while the VN exhibited a variable frequency discharge pattern. The rabbit VN had fewer motor axons (105.3±12.1 vs. 268.1±15.4). Nerve conduction and respiratory function were measured 20 weeks after left PN transection with or without left VN-PN anastomosis. Compared to rabbits subjected to unilateral phrenicotomy without VN-PN anastomosis, diaphragm muscle action potential (AP) amplitude was improved by 292%, distal latency by 695%, peak inspiratory flow (PIF) by 22.6%, peak expiratory flow (PRF) by 36.4%, and tidal volume by 21.8% in the anastomosis group. However, PIF recovery was only 28.0%, PEF 28.2%, and tidal volume 31.2% of Control. Our results suggested that VN-PN anastomosis is a promising therapeutic strategy for partial restoration of diaphragm reinnervation, but further modification and improvements are necessary to realize the full potential of this technique.

Nerve-muscle-endplate band grafting: a new technique for muscle reinnervation

BACKGROUND

Because currently existing reinnervation methods result in poor functional recovery, there is a great need to develop new treatment strategies.

OBJECTIVE

To investigate the efficacy of our recently developed nerve-muscle-endplate band grafting (NMEG) technique for muscle reinnervation.

METHODS

Twenty-five adult rats were used. Sternohyoid (SH) and sternomastoid (SM) muscles served as donor and recipient muscle, respectively. Neural organization of the SH and SM muscles and surgical feasibility of the NMEG technique were determined. An NMEG contained a muscle block, a nerve branch with nerve terminals, and a motor endplate band with numerous neuromuscular junctions. After a 3-month recovery period, the degree of functional recovery was evaluated with a maximal tetanic force measurement. Retrograde horseradish peroxidase tracing was used to track the origin of the motor innervation of the reinnervated muscles. The reinnervated muscles were examined morphohistologically and immunohistochemically to assess the extent of axonal regeneration.

RESULTS

Nerve supply patterns and locations of the motor endplate bands in the SH and SM muscles were documented. The results demonstrated that the reinnervated SM muscles gained motor control from the SH motoneurons. The NMEG technique yielded extensive axonal regeneration and significant recovery of SM muscle force-generating capacity (67% of control). The mean wet weight of the NMEG-reinnervated muscles (87% of control) was greater than that of the denervated SM muscles (36% of control).

CONCLUSION

The NMEG technique resulted in successful muscle reinnervation and functional recovery. This technique holds promise in the treatment of muscle paralysis.

Vocal fold paresis and paralysis: what the thyroid surgeon should know

The thyroid surgeon must have a thorough understanding of laryngeal neuroanatomy and be able to recognize symptoms of vocal fold paresis and paralysis. Neuropraxia may occur even with excellent surgical technique. Patients should be counseled appropriately, particularly if they are professional voice users. Preoperative or early postoperative changes in voice, swallowing, and airway function should prompt immediate referral to an otolaryngologist. Early recognition and treatment may avoid the development of complications and improve patient quality of life.

Vocal fold paresis and paralysis

Diagnosis and treatment of the immobile or hypomobile vocal fold are challenging for the otolaryngologist. True paralysis and paresis result from vocal fold denervation secondary to injury to the laryngeal or vagus nerve. Vocal fold paresis or paralysis may be unilateral or bilateral, central or peripheral, and it may involve the recurrent laryngeal nerve, superior laryngeal nerve, or both. The physician's first responsibility in any case of vocal fold paresis or paralysis is to confirm the diagnosis and be certain that the laryngeal motion impairment is not caused by arytenoid cartilage dislocation or subluxation, cricoarytenoid arthritis or ankylosis, neoplasm, or other mechanical causes. Strobovideolaryngoscopy, endoscopy, radiologic and laboratory studies, and electromyography are all useful diagnostic tools.

Adenoviral GDNF gene transfer enhances neurofunctional recovery after recurrent laryngeal nerve injury

To assess the possibility of gene therapy for recurrent laryngeal nerve (RLN) injury, we examined functional and histological recovery after glial cell line-derived neurotrophic factor (GDNF) gene transfer in a rat RLN crush model. Adenoviral vector encoding beta-galactosidase gene (AxCALacZ) or human GDNF gene (AxCAhGDNF) was injected into the crush site of the RLN. Neurons in the nucleus ambiguus on the crushed side were labeled with X-gal or GDNF immnohistochemistry after AxCALacZ or AxCAhGDNF injection. Reverse transcription-polymerase chain reaction analysis revealed expression of human GDNF mRNA transcripts in brainstem tissue containing the nucleus ambiguus on the crushed side after AxCAhGDNF injection. Animals injected with AxCAhGDNF displayed significantly improved motor nerve conduction velocity of the RLN and recovery rate of vocal fold movement at 2 and 4 weeks after treatment as compared to controls. AxCAhGDNF-injected animals showed a significantly larger axonal diameter and improved remyelination in crushed RLN as compared to controls. Adenoviral GDNF gene transfer may thus promote laryngeal function recovery after RLN injury. Inoculation of adenoviral vector containing the GDNF gene at the site of damage soon after nerve injury may assist patients with laryngeal paralysis caused by nerve injury during head and neck surgery.

Laryngeal reinnervation

Laryngeal reinnervation refers to any of a number of surgical procedures intended to restore neural connections to the larynx, which have usually been lost from some type of trauma (eg, surgical). The nerve function(s) to be restored may be those of the recurrent laryngeal nerve or its subdivisions, those of the superior laryngeal nerve, or both, and they may be motor or sensory. Several different donor nerves are available and have been described. The technique used may be direct end-to-end anastomosis (neurorrhaphy), direct implantation of a nerve ending into a muscle, the nerve-muscle pedicle technique, or muscle-nerve-muscle methods. These nerves and techniques may be combined in many ways. A number of new techniques have been reported in animal studies; however, the animal studies do not always predict the results of analogous surgeries in human patients. The historical and current perspectives on these techniques are discussed in this article.

Voice therapy for vocal fold paralysis

There is no doubt that vocal fold paralysis is a debilitating condition affecting an individual's general health and quality of life. Optimal management of a patient with vocal fold dysfunction by an otolaryngologist, speech scientist, and speech language pathologist results in detailed objective videostroboscopic evaluation of glottal configuration during phonation, acoustic and aerodynamic measures, laryngeal EMG (if appropriate), and the patient's self-rating of vocal disability. Profound glottal incompetence is typically managed surgically with a few voice therapy sessions after surgery to ensure optimal vocal function. Patients with more adequate glottal closure are often seen for voice therapy and lost to follow-up when their voices improve enough to satisfy their vocal needs. It is essential that a complete battery of assessments, including perceptual, aerodynamic, acoustic, and stroboscopic measures, be obtained at periodic intervals in surgical and nonsurgical patients so as to evaluate vocal function over time. One of the few rigorous studies of perceptual, acoustic, aerodynamic, and videofiberscopic findings in patients after medialization with fat and thyroplasty assessed patients before surgery and at short (1-3 months),middle (4-6 months), and long (7-12 months) intervals after surgery. Improvement in most parameters at short- and long-term intervals was noted but not in the middle interval. The best results were obtained in women. Continued difficulty in increasing and maintaining subglottal pressure for high-intensity phonation was observed in both male and female patients. This fine study raises a number of questions as follows. What objective phonatory measures should be assessed before and after intervention and at what time intervals? Why were the women's results better than the men's results when no correlation of age, pulmonary function, or severity of preoperative voice and aerodynamic impairment was observed? Should voice therapy be initiated at the 4- to 6-month interval when voice quality diminished or within 1 to 2 months after surgery so that the decrement in vocal function might not occur? Why did vocal function ultimately improve after 7 to 12 months? Heuer et al and Colton and Casper found similar outcome satisfaction in patients electing surgery compared with those that were seen for voice therapy; however, the patients with lesser glottal incompetence in both studies opted for therapy. Can we better define vocal parameters that help to predict which patients may need surgery rather than therapy? Should all patients with high airflow measures but near-normal subglottal pressures and MPT greater than 10 seconds undergo 6 weeks of voice therapy rather than medical intervention? If all surgical patients were seen for 6 weeks of postoperative therapy, would voice satisfaction ratings increase to greater than 70%? Can we perceptively or objectively differentiate patients whose postoperative voices will be excellent from those whose voices will be merely adequate? These questions can only be answered by the development and implementation of a rigorous protocol studying women and men of varying ages with unilateral vocal fold paralysis choosing medialization surgery and electing voice therapy. Standardized assessments must include perceptual,aerodynamic, acoustic, stroboscopic, and patient satisfaction measures during soft- and loud-intensity tasks before and at periodic intervals after the two interventions.

Delivery of an adenoviral vector to the crushed recurrent laryngeal nerve

OBJECTIVES

Objectives were to create a model of recurrent laryngeal nerve injury for testing the efficacy of potential therapeutic viral gene therapy vectors and to demonstrate that remote injection of a viral vector does not cause significant additional neuronal injury.

STUDY DESIGN

Animal model.

METHODS

Rats were randomly assigned to three groups of 10 animals each. In group I, the recurrent laryngeal nerve was crushed. In group II, the nerve was crushed and then injected with an adenoviral vector containing no transgene. In group III, the nerve was identified but was not crushed. Rats were killed at 1 week, and their larynges and brainstems were cryosectioned in 15-microm sections. Laryngeal cryosections were processed for acetylcholine histochemical analysis (motor endplates) followed by neurofilament immunoperoxidase (nerve fibers). Percentage of nerve-endplate contact was determined and compared between groups. Fluorescent in situ hybridization was performed on brainstem sections from rats in group II to confirm the presence of virus.

RESULTS

No significant difference in percentage of nerve-endplate contact exists between the two crushed-nerve groups (groups I and II) (P =.88). The difference between both crushed-nerve groups and the group with noncrushed nerves (group III) was highly significant (P <.0001). The presence of virus was confirmed in group II rats.

CONCLUSIONS

Crush provides a significant measurable injury to the recurrent laryngeal nerve and may be used as a model to explore therapeutic interventions for nerve injury. The remote injection of viral vector did not cause significant additional neuronal injury. Remote delivery of viral vectors to the central nervous system holds promise in the treatment of recurrent laryngeal nerve injury and central nervous system diseases.

Laser tenotomy and vocal process resection for bilateral midline vocal fold fixation

BACKGROUND

The present retrospective study presents the outcomes of a group of 21 patients with laryngeal obstruction caused by bilateral vocal fold fixation. All of these patients were treated by laser assisted muscle tenotomy and vocal process resection - a modification of the technique described by Michael and Eugene Rontal in 1994.1

METHODS

Between January 1997 and March 2002 the senior author performed muscle tenotomy and vocal process resection for bilateral vocal fold fixation on 21 patients.

RESULTS

The mean follow-up time was 2.3 years. The technique was successful in achieving an adequate airway and good voice with no aspiration in every case.

CONCLUSIONS

Laser assisted muscle tenotomy and vocal process resection is a proven treatment for bilateral medial vocal fold fixation with the provision of a good airway, good voice and the avoidance of aspiration.

Electromyographic findings in recurrent laryngeal nerve reinnervation

Abductor, adductor, and combined reinnervation procedures have been explored with variable success rates. We describe the experience of a tertiary care center with adductor reinnervation procedures, including preoperative and postoperative videostroboscopy and electromyography (EMG) findings. A retrospective chart review was performed from 1997 to 2001 that included 9 patients. Preoperative and postoperative voice comparison was performed by 3 blinded speech pathologists. Clinical comparisons of videostroboscopy findings for vocal fold bulk, tone, position, presence of gap, and movement are elucidated. The preoperative and postoperative EMG findings are described. In all patients, preoperative EMG revealed a dense, complete denervation of the affected recurrent laryngeal nerve. No movement was noted on videostroboscopy with persistent glottic gap. Reinnervation involved a nerve-muscle pedicle or a direct neurorrhaphy of the ansa cervicalis to the recurrent laryngeal nerve. Voice improvement was noted between 60 days and 3 months after reinnervation. Four postoperative EMG studies were performed. An early postoperative EMG study at 5 months revealed activation of the lateral cricoarytenoid muscle and thyroarytenoid muscle with head-lift. Videostroboscopy showed excellent near-midline static positioning of the vocal fold. Late EMG studies, performed 12 to 16 months after reinnervation, revealed "learning" of these muscles, with new activation on "eee" phonation. We conclude that recurrent laryngeal nerve reinnervation procedures belong in the armamentarium of the laryngologist for the treatment of vocal fold paralysis. The EMG findings reported in this study suggest that ongoing reinnervation allows for activation with phonation in matured neuronal anastomoses. Overall, this procedure results in excellent patient acceptance and near-normal vocal quality.

Remote delivery of rAAV-GFP to the rat brainstem through the recurrent laryngeal nerve

OBJECTIVE

To demonstrate that a recombinant adeno-associated viral vector (rAAV) carrying the gene for green fluorescent protein (GFP) could be delivered to the rat brainstem by remote injection into the recurrent laryngeal nerve.

STUDY DESIGN/METHODS

rAAV-GFP is a serotype 2 adeno-associated vector containing the cDNA of GFP and woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) under the control of the CAG promoter (obtained from Matthew During, PhD, Thomas Jefferson Medical College). Five microliters or 10 microL of 1.4 x 109 particles/microL of rAAV-GFP were injected into the right recurrent laryngeal nerve of adult Sprague-Dawley rats. Rats were killed and perfused at 3 (n = 3) and 11 weeks (n = 3). Brainstems were removed and cryosectioned. Fluorescent in-situ hybridization (FISH) was performed on cryosections from animals killed at 3 weeks using a cDNA probe for woodchuck polyribosomal enzyme within the rAAV vector. In a third group (n = 2), Fluoro-Gold (Fluorochrome, Inc., Denver, CO) was injected into the right thyroarytenoid muscle for comparison of neuronal uptake distribution. These rats were killed and perfused at 3 weeks.

RESULTS

The presence of GFP was noted in neurons throughout the medulla of all rat brainstems after unilateral rAAV-GFP injection at both 3 and 11 weeks. In contrast to the Fluoro-Gold, GFP was noted bilaterally and outside of the nucleus ambiguus. FISH confirmed the presence of virus within neurons expressing GFP at 3 weeks.

CONCLUSIONS

Remote delivery of rAAV-GFP to the rat brainstem is possible through injection into the recurrent laryngeal nerve. This has important therapeutic implications for the future treatment of recurrent laryngeal nerve injury and neurodegenerative diseases.

Motion-specific laryngeal reinnervation using muscle-nerve-muscle neurotization

There is no current treatment method that can reliably restore physiologic movement to a paralyzed vocal fold. The purposes of this study were to test the hypotheses that 1) muscle-nerve-muscle (M-N-M) neurotization can be induced in feline laryngeal muscles and 2) M-N-M neurotization can restore movement to a paralyzed vocal fold. Muscle-nerve-muscle neurotization can be defined as the reinnervation of a denervated muscle via axons that are induced to sprout from nerves within an innervated muscle and that then traverse a nerve graft interposed between it and the target denervated muscle. A paralyzed laryngeal muscle could be reinnervated by axons from its contralateral paired muscle, thus achieving motion-specific reinnervation. Eighteen adult cats were divided into sham, hemilaryngeal-denervated, and M-N-M-reinnervated thyroarytenoid muscle groups. Five of the 6 reinnervated animals had histologic evidence of axons in the nerve graft, 4 of the 6 had evoked electromyographic evidence of crossed reinnervation, and 1 of the 6 had a return of appropriately phased adduction. This technique has great potential and should be further investigated.

Critical evaluation of neurolaryngological disorders

Otolaryngological examinations, videostroboscopic image analysis, and laryngeal electromyography were used as a test battery for a critical evaluation in 80 patients. Vocal fold movements were categorized into mobility, restricted mobility, immobility with different positions, and overactive movement. Laryngeal electromyographic examinations were conducted in all patients, and the results were classified into normal, neuropathic, and myopathic patterns. The electromyographic data were integrated with videostroboscopic findings, interpreted with knowledge of biomechanical and electrophysiological mechanisms of the larynx, and correlated clinically with underlying diseases. It is suggested that neurolaryngological procedures are most clinically useful when dictated by a decision-making algorithm.

Voice disorders in children

Pediatric patients with voice or speech problems usually should receive a team assessment in which communication between the pediatrician or primary care physician, the otolaryngologist, and speech pathologist occurs. Although speech or voice problems may prompt an otolaryngologic evaluation, the voice or speech problem simply may be the manifestation or symptom of a larger or more complex disease process. Whether that is the case of hypernasal speech, eventually leading to the diagnosis of velocardiofacial syndrome, or bilateral vocal fold paralysis, eventually leading to the diagnosis of hydrocephalus, it is apparent that patients with speech or voice disorders may eventually require multidisciplinary evaluation. The outlook for children with speech and voice difficulties is better than ever. Recent equipment advances, such as flexible laryngoscopy, video stroboscopy, and nasometry, for detection, evaluation, and management of speech problems have created a better environment than ever existed for care of these problems. Much research is being performed in the area of pediatric voice and speech problems. The National Institute of Deafness and Communicative Disorders and the National Institute of Dental Research have funded and currently fund many projects in these areas. Many pediatric hospitals now have voice or speech disorder clinics in which multiple disciplines are brought together to evaluate children with these problems. Children benefit best when speech and voice problems are managed in an interdisciplinary setting when necessary and by professionals who have experience and training in these specialized pediatric problems. Given the local, professional, and national resources that are expended toward recognition and treatment of speech disorders in children, it is truly a tragedy when those resources cannot be brought to assist children with voice and speech problems. Although voice and speech problems usually are recognized by parents or concerned family members, this task may rest on the pediatrician or other primary caregiver.

Unilateral vocal fold paralysis: a review of the current methods of surgical rehabilitation

This review article discusses the surgical treatment of patients suffering from unilateral vocal fold paralysis who have already been assessed and considered appropriate candidates for surgery. There are currently three main methods of surgical rehabilitation; injection medialisation; laryngeal framework surgery; re-innervation procedures.

The role of stroboscopy in the management of a patient with a unilateral vocal fold paralysis

Stroboscopy is well established as an essential diagnostic tool in the assessment of the vocal folds during phonation. This paper analyses the stroboscopic findings in 100 patients with a unilateral vocal fold paralysis. Reliable stroboscopic signals were only obtained in patients with the paralysed fold close to the midline. These patients seldom require surgery however, usually responding to speech therapy with laryngeal compensation giving a good voice. Most patients that require surgery have a large glottal deficiency, but in this series these patients did not give an adequate signal for analysis. Although useful in the assessment of the muscle tone of the paralysed fold, the influence of stroboscopy on the surgical treatment in this series was limited.

Use of laryngeal muscular tenotomy for bilateral midline vocal cord fixation

As experience has increased in the treatment of bilateral vocal cord fixation, a significant and fundamental refinement in the concept of repair has evolved. By the use of selective tenotomy of the interarytenoid and thyroarytenoid muscles, the arytenoid and the vocal cord can be made to move away from the midline and thus open the glottis. This has allowed a drastic reduction in the amount of arytenoid that must be removed and prevents both aspiration and arthritis of the joint with subsequent stiffness. The procedure can be performed as an endoscopic or microscopic open procedure. All eight patients treated by this method have been decannulated by 6 weeks postoperation, have returned to full function, have not had aspiration, and have no worsening of their voices. The use of this concept and technique has led to a relatively safe and reliable method of rehabilitating patients with bilateral midline vocal cord paralysis.