The use of readily available equipment in a simple method for intraoperative monitoring of recurrent laryngeal nerve function during thyroid surgery: initial experience with more than 300 cases

HYPOTHESIS

An inexpensive and widely applicable technique to monitor recurrent laryngeal nerve (RLN) function during thyroid surgery can be safely implemented.

DESIGN

Consecutive sample.

SETTING

Single-surgeon academic practice.

PATIENTS

Three hundred sixty-three consecutive patients undergoing surgery for thyroid disease in the 18 months from November 1, 1999, to May 31, 2001.

INTERVENTIONS

Anesthetic management using laryngeal mask airway and spontaneous ventilation, combined with electrical RLN stimulation and fiberoptic video laryngoscopy to confirm vocal cord response.

MAIN OUTCOME MEASURES

Vocal cord response to RLN stimulation, intraoperative anatomic findings, postoperative voice quality, and anesthetic complications.

RESULTS

We used the laryngeal mask airway-based technique in 327 cases. Visualization of vocal cords was maintained throughout the surgery in 310 cases (95%). In 10 cases (3%), the branch of the RLN carrying vocal cord function could not be identified until electrical testing was performed. A single inadvertent RLN palsy was seen in 1 of the 17 cases in which vocal cord visualization was lost during the procedure (0.03% overall). Upper airway obstruction occurred in 16 (5%) of 327 attempted procedures, requiring tracheal intubation in 3 (1%). No further complications regarding airway management were seen. Pneumothorax was observed in 5 cases (2%), each of which resolved without chest tube placement.

CONCLUSIONS

This technique can be applied to thyroid surgery as a safe means of managing the airway. It is associated with an ability to test RLN function at will in more than 95% of cases using readily available equipment.

Internal superior laryngeal nerve afferent activity during respiration and evoked vocalization in cats

The purpose of this project was to identify and categorize patterns of activity of the internal branch of the superior laryngeal nerve during vocalization evoked by midbrain stimulation in cats anesthetized with alpha-chloralose. Unit activity was isolated from the cut distal end of the internal branch of the superior laryngeal nerve by means of floating bipolar electrodes that retained their contact with nerve fibers despite movement due to vocalization. The phases of respiration and vocalization were determined with a diaphragm electromyogram, a photoglottogram, and a microphone recording. Five groups of discrete afferent activities were defined according to relationships between the spike activity and the phases of vocalization. Group 1 cell activity peaked just before phonation, during expiratory airflow (n = 26). Group 2 cells (n = 19) followed a vocal fold vibratory pattern during phonation. Group 3 cell activity (n = 6) peaked during phonation, but did not follow vocal fold vibration. Group 4 cells (n = 3) were active during inspiration between phonations. Group 5 cells (n = 4) showed both inspiratory and expiratory modulation. These results indicate that laryngeal afferent activity responds to phonation-specific events during vocalization. This stereotyped afferent information might be used by the central nervous system to modulate vocalization.

Modulation of myosin heavy chains in rat laryngeal muscle

OBJECTIVES

To test the hypothesis that myosin heavy chain (MHC) composition is a biological marker indicative of appropriate and functional reinnervation.

STUDY DESIGN

Age-matched adult rats were randomized for prospective study under three experimental conditions.

METHODS

In adult rats, three experimental conditions were surgically created, including transient recurrent laryngeal nerve (RLN) crush injury, RLN transection and repair, and cricoarytenoid joint fixation with intact RLN. Animals were survived for 30, 90, and 180 days. At each interval, vocal fold mobility was assessed by rigid microlaryngoscopy. Laryngeal electromyography (EMG) was performed before euthanasia. The thyroarytenoid and posterior cricoarytenoid muscles were then excised, each muscle was processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and MHC composition was determined.

RESULTS

Thirty days after nerve crush injury, three of six animals regained vocal fold mobility and normal MHC composition. Impaired vocal fold motion in three of six animals was associated with MHC composition characteristic of denervation. At 90 and 180 days, normal vocal fold motion and normal MHC composition were observed in all animals. Following nerve transection and repair, impaired vocal fold motion and MHC composition characteristic of denervation were observed in all animals, despite evidence of reinnervation on EMG. Following joint fixation, alteration in MHC composition consistent with denervation was observed only at 30 days, as was evident in the nerve crush model.

CONCLUSION

Temporary injury and vocal fold immobilization result in transient shifts in MHC composition. Nerve transection and repair result in persistent alteration of MHC composition and vocal fold dysfunction. The expression of normal MHC composition is dependent on the condition of appropriate neural contact and functional reinnervation.

Arytenoid appearance and vertical level difference between the paralyzed and innervated vocal cords

OBJECTIVES/HYPOTHESIS

In unilateral vocal fold paralysis, it has been generally accepted that the paralyzed vocal fold presents at a higher level than a normally innervated vocal fold. In this study, we correlate the appearances of the paralyzed arytenoid and the differences in level between the paralyzed and innervated vocal folds.

STUDY DESIGN

Retrospective review using video-recorded images of larynx.

METHODS

A total of 38 patients were selected for this study who reported symptoms of voice change attributable to a paralyzed vocal fold unilaterally. Video recordings were obtained using the laryngeal telescope. The heights were assessed according to the paralyzed positions, status (inspiration or phonation), and appearances of the paralyzed arytenoid. The appearances of paralyzed arytenoid were further clarified as the portions of the medial surface of the arytenoid that were visualized.

RESULTS

In medial paralysis, the paralyzed vocal fold appeared mainly as being at an equal vertical level or as having no distinct difference from normal vocal fold during phonation. However, a few cases of medial paralysis showed a lower than normal or higher than normal vocal fold during phonation, depending on the appearance of the paralyzed arytenoid. In lateral paralysis, most of the paralyzed vocal folds were not higher than the innervated vocal folds during phonation.

CONCLUSIONS

The heights of paralyzed vocal folds were variable depending on the paralyzed positions, the status of the larynx, and appearances of the paralyzed arytenoid. The fact that the paralyzed vocal fold is at a higher level than the normal vocal fold should be reconsidered.

Irregular vocal-fold vibration--high-speed observation and modeling

Direct observations of nonstationary asymmetric vocal-fold oscillations are reported. Complex time series of the left and the right vocal-fold vibrations are extracted from digital high-speed image sequences separately. The dynamics of the corresponding high-speed glottograms reveals transitions between low-dimensional attractors such as subharmonic and quasiperiodic oscillations. The spectral components of either oscillation are given by positive linear combinations of two fundamental frequencies. Their ratio is determined from the high-speed sequences and is used as a parameter of laryngeal asymmetry in model calculations. The parameters of a simplified asymmetric two-mass model of the larynx are preset by using experimental data. Its bifurcation structure is explored in order to fit simulations to the observed time series. Appropriate parameter settings allow the reproduction of time series and differentiated amplitude contours with quantitative agreement. In particular, several phase-locked episodes ranging from 4:5 to 2:3 rhythms are generated realistically with the model.

Possible roles for GABAergic inhibition in the vocal control system of the zebra finch

The final common output from the telencephalic vocal control system in songbirds is the projection from nucleus RA, which drives respiratory and syringeal muscles via medullary nuclei. We examined the possible role of GABAergic inhibition in RA of adult male zebra finches by micro-injecting bicuculline, an antagonist of inhibitory GABA(A) receptors, while recording simultaneously with multiple microelectrodes. Following bicuculline injection, the normally high spontaneous activity of RA neurons exhibited a pattern of rhythmic bursting lasting up to 30 min. The bursts were often accompanied by involuntary vocalizations: monosyllabic notes resembling calls. Other experiments used microinjections that were below threshold for involuntary vocalization. When the bird sang to a female during a period after the injection, song structure was degraded: song duration was lengthened, noisiness increased, and novel syllables appeared. The results suggest that GABA normally contributes to regulating excitability in RA. When this regulation is blocked, activity increases sufficiently to engage the respiratory and vocal musculature. Synaptic inputs that affect GABAergic interneurons in RA could thus play a role in initiation and control of vocalization. The abnormal vocalizations produced in the presence of bicuculline suggest that GABAergic inhibition may normally help to shape the pattern of learned vocalizations, as well as to regulate overall RA activity.

Morphometric study of nucleus ambiguus in multiple system atrophy presenting with vocal cord abductor paralysis

AIM

To identify lesions responsible for vocal cord abductor paralysis (VCAP) in multiple system atrophy (MSA), we performed a morphometric study of the nucleus ambiguus which innervates the intrinsic laryngeal muscles.

METHODS

Two autopsied cases of MSA presenting with VCAP and one control were examined. Both cases of MSA showed selective neurogenic atrophy of the posterior cricoarytenoid muscles among the intrinsic laryngeal muscles, while no abnormalities were seen in the control. From a block of the medulla oblongata, sections 10 microm thickness were cut serially without spacing and stained with cresyl violet. The ambiguus neurons were counted in all the sections to make a histogram.

RESULTS

In the control case, ambiguus neurons showed densely populated areas and sparsely populated areas alternately with significant difference in the mean neuronal density between two areas. In MSA, ambiguus neurons were significantly decreased in number at all levels. It indicates that the neurogenic atrophy of the posterior cricoarytenoid muscle is derived from the neuronal loss of the nucleus ambiguus.

CONCLUSION

Though it has still been controversial whether or not the ambiguus neurons are decreased in number in MSA with VCAP, we speculated possible reasons for the disagreement on the involvement of the nucleus ambiguus as follows: different mechanism of VCAP are playing role, and histometric data have been disturbed by factors such as split-cell counting error and marked variation in the distribution of the ambiguus neurons.

Laryngeal reflexomyographic responses in rabbits: a neurolaryngological study of glottal movement

The role of the laryngeal reflex in glottal movement has been reported, but its mechanism remains unclear. To further investigate the neurophysiological characteristics of glottal movement, we recorded the laryngeal reflexomyographic responses (LRMRs) to electrical stimulation of the superior laryngeal nerve (SLN) in rabbits. The procedure involved simultaneous recording of the LRMRs from the thyroarytenoid muscles by means of bipolar hooked wire electrodes after electrical stimulation to the SLN. The results demonstrated characteristic patterns of the responses, consisting of R1 and R2, similar to those found in humans. The R1 response was obtained with a latency of 10.7 +/- 0.78 ms. The ipsilateral R2 response was obtained with a latency of 43.76 +/- 4.67 ms in all rabbits, and the contralateral R2 response with a latency from 42.6 to 50.2 ms in 4 rabbits. It was concluded that LRMRs may serve as a potential central laryngeal function test in the investigation of glottal movement control.

Effects of lesions of the central nucleus of the anterior archistriatum on contact call and warble song production in the budgerigar (Melopsittacus undulatus)

We studied the effects of both unilateral and bilateral lesions of the central nucleus of the anterior archistriatum (AAc) on the production of contact calls and warble song in adult male and female budgerigars. Birds were sorted into three experimental groups based on the percentage of AAc destroyed and whether lesions were unilateral or bilateral. The experimental groups were Unilateral Lesion (N = 8), Partial Bilateral Lesion (N = 5), and Bilateral Lesion birds (N = 12). Each group contained both sexes. Unilateral lesions had no demonstrable effects on contact call or warble song production. Bilateral lesions resulted in immediate and permanent disruption of all learned temporal and spectral characteristics of contact calls, although call initiation was not dependent on the AAc. Partial bilateral lesion effects varied with lesion size and location. At least 20-30% sparing of the AAc, including sparing portions of both the dorsal (AAcd) and ventral (AAcv) subdivisions on the same side of the brain, is necessary for production of prelesion contact call patterns. Warble song was absent in birds with complete bilateral destruction. Two birds with large yet incomplete lesions of the AAc sang after surgery, although the warble song of these birds was extremely impoverished and contained only a few of the typical warble song elements. Lesion results indicate that the AAc mediates the production of learned vocal features in male and female budgerigars, with each hemisphere capable of supporting a normal vocal repertoire.

Laryngeal adductory pressure as a measure of post-reinnervation synkinesis

Laryngeal adductory pressure (LAP) is the pressure induced as the vocal folds squeeze on a balloon while the recurrent laryngeal nerve (RLN) is stimulated. The LAP has been shown to vary with the frequency of stimulation, with a characteristic slope. The RLN was divided and reanastomosed 4 different ways in 12 canine hemilaryngeal preparations; the 4 subgroups represented a range of expected post-reinnervation synkinesis recovery patterns. The LAP frequency-response curve was measured before surgery and at monthly intervals for 6 months after surgery. In the "best-case" group (RLN adductor and abductor trunks each divided and reanastomosed), the slope was found to return to normal. The 2 whole RLN division-reanastomosis groups (precise realignment or 180 degrees rotation) both gave results similar to those of the "worst-case" group (RLN adductor and abductor trunks divided and transposed); these 3 subgroups were all significantly different from baseline. The slope of the LAP frequency-response curve may be a useful means of indirectly quantifying laryngeal synkinesis.

Chemodenervation of the rat hemilarynx with phenol

In this study, the injection of phenol into the true vocal fold was evaluated on a rat model as a possible treatment for adductor spasmodic dysphonia. A 10% phenol solution was injected into the right true vocal fold. Quantitative measurement of vocal fold adductory force showed reduction to 35% of the preinjection value 3 months after injection (p < .05). Qualitative evaluation by videolaryngoscopy demonstrated maintenance of the normal vocal fold range of motion. Histologic studies showed a transient inflammatory infiltrate and myolysis, while the vocal fold mucosa and the cricoarytenoid joints remained undamaged. Further investigation into the potential use of phenol for treating spasmodic dysphonia is warranted.

Paradoxical vocal fold motion: presentation and treatment options

Paradoxical vocal fold motion is a rare disorder in which adduction of the folds occurs on inspiration. The disorder presents with signs of airway obstruction and often airway distress, so proper diagnosis by the otorhinolaryngologist is critical to subsequent management. We present a retrospective review of 10 patients with the diagnosis of paradoxical vocal fold motion seen over a 6-year period. Eight patients were females, and 6 required an acute airway intervention at presentation; 3 patients eventually underwent tracheotomy for respiratory decompensation. Six patients had a prior diagnosis of asthma, and this was determined to contribute to their respiratory status. Five patients were treated with botulinum toxin and 2 with flexible nasolaryngoscopic biofeedback, which improved the outcome. A review of the literature confirms a female predominance of patients presenting with paradoxical adduction and airway distress, often with a history of asthma and psychopathology. Our experience with botulinum toxin and biofeedback suggests that these procedures are viable treatment options in the management of patients with this disorder.

Combined arytenoid adduction and laryngeal reinnervation in the treatment of vocal fold paralysis

OBJECTIVE/HYPOTHESIS

Glottal closure and symmetrical thyroarytenoid stiffness are two important functional characteristics of normal phonatory posture. In the treatment of unilateral vocal cord paralysis, vocal fold medialization improves closure, facilitating entrainment of both vocal folds for improved phonation, and reinnervation is purported to maintain vocal fold bulk and stiffness. A combination of medialization and reinnervation would be expected to further improve vocal quality over medialization alone.

STUDY DESIGN

A retrospective review of preoperative and postoperative voice analysis on all patients who underwent arytenoid adduction alone (adduction group) or combined arytenoid adduction and ansa cervicalis to recurrent laryngeal nerve anastomosis (combined group) between 1989 and 1995 for the treatment of unilateral vocal cord paralysis. Patients without postoperative voice analysis were invited back for its completion. A perceptual analysis was designed and completed.

METHODS

Videostroboscopic measures of glottal closure, mucosal wave, and symmetry were rated. Aerodynamic parameters of laryngeal airflow and subglottic pressure were measured. A 2-second segment of sustained vowel was used for perceptual analysis by means of a panel of voice professionals and a rating system. Statistical calculations were performed at a significance level of P = .05.

RESULTS

There were 9 patients in the adduction group and 10 patients in the combined group. Closure and mucosal wave improved significantly in both groups. Airflow decreased in both groups, but the decrease reached statistical significance only in the adduction group. Subglottic pressure remained unchanged in both groups. Both groups had significant perceptual improvement of voice quality. In all tested parameters the extent of improvement was similar in both groups.

CONCLUSION

The role of laryngeal reinnervation in the treatment of unilateral vocal cord paralysis remains to be established.

Long-term preservation of voice improvement following surgical medialization and reinnervation for unilateral vocal fold paralysis

In June of 1996, we reported improved functional voice results when reinnervation was combined with surgical medialization for unilateral vocal fold paralysis. In addition, it was noted that further wasting of the reinnervated vocal fold was prevented in 96% of these patients beyond 2 years' follow-up. The study reported here compares the long-term preservation of voice improvement achieved by surgical medialization alone with that resulting from combined medialization and nerve-muscle pedicle reinnervation. Further significant wasting of the paralyzed vocal fold with voice deterioration from that achieved by surgical medialization alone was noted between 6 months and 2 years postoperatively in 28% of patients, while only 4% of those undergoing combined reinnervation demonstrated this finding at a minimum of 2 years' follow-up.

[Measuring therapy success in laryngeal paralysis based on voice parameters]

The clinical courses of vocal rehabilitation of patients with different degrees of laryngeal paralysis can proceed very differently, but usually do not correspond with the physical changes of glottic function seen on laryngoscopy and stroboscopy. In this study 43 patients with laryngeal paralyses were examined, of whom 28 had regeneration of nerve function. Fifteen did not show any improvement in glottal function. All patients were asked to describe their voices, after which subjective data were compared to objective findings concerning vocal penetrating capacity, voice attack, volume, and capacity. In particular, voice capacity, attack, and vocal penetrating capacity were found to be valid in reflecting therapeutic effects and for estimating voice capability.

Changes in adult zebra finch song require a forebrain nucleus that is not necessary for song production

Male zebra finches normally crystallize song at approximately 90 days and do not show vocal plasticity as adults. However, changes to adult song do occur after unilateral tracheosyringeal (ts) nerve injury, which denervates one side of the vocal organ. We examined the effect of placing bilateral lesions in LMAN (a nucleus required for song development but not for song maintenance in adults) upon the song plasticity that is induced by ts nerve injury in adults. The songs of birds that received bilateral lesions within LMAN followed by right ts nerve injury silenced, on average, 0.25 syllables, and added 0.125 syllables (for an average turnover of 0.375 syllables), and changed neither the frequency with which individual syllables occurred within songs nor the motif types they used most often. In contrast, the songs of birds that received sham lesions followed by ts nerve injury lost, on average, 1.625 syllables, silenced 0.125 syllables, and added 0.75 syllables, turning over an average of 2.5 syllables. They also significantly changed both the frequency with which individual syllables were included in songs and the motif variants used. Thus, song plasticity induced in adult zebra finches with crystallized songs requires the presence of LMAN, a nucleus which had been thought to play a role in vocal production only during song learning. Although the changes to adult songs induced by nerve transection are more limited than those that arise during song development, the same circuitry appears to underlie both types of plasticity.

Innervation and reinnervation of cricothyroid muscle in the rabbit

The m. cricothyroideus of the rabbit is innervated by two motor nerves (n. laryngeus superior and n. laryngeus medius). No indication of extensive polyneuronal innervation was found in gold stained isolated muscle fibers and groups of fibers. Double end plates were found on about 2.5% of the fibers. It could not be ascertained whether they were supplied by different motor fibers or by branches of the same fiber. Intracellularly recorded spike potentials were observed in the same muscle fiber by stimulation of the two motor nerves in 6% of the fibers examined. The use of intracellular recording as a criterion for polyneuronal innervation was discussed. After resection of the n. laryngeus medius a fargoing reinnervation of the muscle by the n. laryngeus superior takes place.

The muscular tissue of the vestibular folds of the larynx

The muscular tissue of the vestibular folds was investigated in plastinated serial sections of 32 normal adult larynges. Three muscular systems could be distinguished. A posterolateral muscle layer was found to be developed at the lateral margin of the posterior part of the vestibular fold. Its fibers extended in a sagittal direction, and their contraction probably resulted in an adduction of the entire tissue of the vestibular fold towards the midline. Within the anterior part of the vestibular fold, an anterolateral muscle sheet was seen to attach to the thyroid cartilage. An anteromedial muscular system consisted of scattered groups of muscle fibers situated medially and dorsally to the laryngeal ventricle and saccule. These fibers were presumed to exert a downward pressure on the vestibular folds, in addition to an adductor function. According to clinical experience, adductor movements of the vestibular folds can be trained, even in cases with a recurrent laryngeal nerve lesion, in order to produce a compensatory voice. Thus, the muscles of the vestibular folds are probably innervated by the superior laryngeal nerve.

Objective measures of laryngeal function after reinnervation of the anterior and posterior recurrent laryngeal nerve branches

Previous research indicates that separate reinnervation of the anterior and posterior branches of the recurrent laryngeal nerve (RLN) can provide purposeful motion of the larynx, even after transplantation. This canine study was undertaken to better determine the results of RLN reinnervation after nerve transection distal to its bifurcation. This approximates ideal conditions for transplantation, because potential rejection and nerve branch mismatch are eliminated. Eight months after nerve repair, video, electromyographic, mechanical, and histologic data were collected on four canines. Results show return of appropriate motion without synkinesis, including purposeful abduction on endotracheal tube occlusion. Abductory function was weaker on the reinnervated side, but adduction was equal or stronger on the reinnervated vocal cord. These results indicate that this method of RLN reinnervation produces consistent, strong physiologic motion in the denervated larynx.

[Modified posterior Dennis and Kashima cordectomy in treatment of bilateral recurrent nerve paralysis]

BACKGROUND

A number of different surgical methods are described in the literature to enlarge the glottic gap in patients with bilateral recurrent nerve paralysis with an excessively small glottic gap. The latest method is the posterior chordectomy described by Dennis and Kashima.

PATIENTS AND METHODS

Twenty-three patients with bilateral recurrent nerve paralysis were treated between 1993 and 1997. In the first 5 patients, a muscular triangle as described by Dennis and Kashima from the posterior part of the muscular portion of the vocal fold was resected. Later on, the surgical procedure was extended by additional resection of muscular tissue from the anterior two-thirds of the vocal fold. Preoperative and postoperative data were carefully assessed in a prospective setting. Subjective data such as limitation of physical exertion and ability to communicate were documented. There was objective documentation by spirometry and phoniatric-logopedic assessment of voice quality parameters. Generally, it takes a number of months until the final permanent state is reached. The minimum follow-up was therefore at least 6 months with a mean of 16 months.

RESULTS

The follow-up of the 23 patients showed that the surgical technique as originally described by Dennis and Kashima does not always improve breathing sufficiently in the long run. A repeat chordectomy was required in three out of five patients with this technique. The modified technique with additional muscle resection of the anterior two-thirds of the vocal fold resulted in the desired long-term enlargement of the glottic gap in 16 out of 18 patients. Spirometric controls showed a significant improvement of respiration. However, some voice quality parameters showed a significant reduction as expected. Despite this, the overall communication ability was described as only slightly reduced by the patients themselves.

CONCLUSIONS

By the modified posterior laser chordectomy, the glottic gap is widened on a long term, though less than after an arytenoidectomy. The compromise between reduction of voice quality and dyspnoea is better than after arytenoidectomy. The preservation of the laryngeal sphincter is important in that it prevents the latent aspirations that are occasionally observed and achieves a certain adduction of the vocal folds with phonation. The surgical procedure is technically simple, may be repeated, and never needs a tracheostomy.

Cross-innervation of the thyroarytenoid muscle by a branch from the external division of the superior laryngeal nerve

The neuroanatomy of the larynx was explored in seven dogs to assess whether there is motor innervation to the thyroarytenoid (TA) muscle from the external division of the superior laryngeal nerve (ExSLN). In 3 animals, such innervation was identified. Electrical stimulation of microelectrodes applied to the ExSLN resulted in contraction of the TA muscle, indicating that this nerve is motor in function. This was confirmed by electromyographic recordings from the TA muscle. Videolaryngostroboscopy revealed improvement in vocal fold vibration following stimulation of the ExSLN compared to without it. Previously, the TA muscle was thought to be innervated solely by the recurrent laryngeal nerve. This additional pathway from the ExSLN to the TA muscle may have important clinical implications in the treatment of neurologic laryngeal disorders such as adductor spasmodic dysphonia.

Loss of large myelinated nerve fibres of the recurrent laryngeal nerve in patients with multiple system atrophy and vocal cord palsy

OBJECTIVES

Vocal cord palsy seen in some patients with multiple system atrophy may result from neuronopathy of the recurrent laryngeal nerve.

METHODS

Six controls and six patients with multiple system atrophy, four with and two without vocal cord palsy were studied. The number of myelinated nerve fibres were counted and fibre diameter histograms were established for the motor and sensory divisions of the laryngeal branch of the recurrent laryngeal nerve.

RESULTS

Although both groups of patients with multiple system atrophy showed selective loss of the myelinated fibres in the motor branch, the change was greater in those with vocal cord palsy than in those without. The small myelinated nerve fibres (diameter < 7 microm) were decreased in number in both multiple system atrophy groups, whereas the large myelinated nerve fibres (diameter < 8 microm) were decreased only in those with vocal cord palsy, and preserved in those without the symptom.

CONCLUSION

In multiple system atrophy, the small myelinated fibres innervating the vocal cord are affected first, without obvious clinical signs. The patient develops vocal cord palsy only after the loss of the large myelinated fibres, which mostly comprise the alpha motor axons that innervate the intrinsic laryngeal muscles.

Correlation between instability of fundamental voice frequency and malignant infiltration of vocal fold nerve endings

Performing systematically acoustical objective voice analysis in patients with chronic chorditis and glottic cancer we detected a certain number of cases with exceptional acoustical pattern. In 7 of 50 patients with chronic chorditis this acoustical pattern was highly specific demonstrating frequent changes of fundamental frequency in short time interval. In 31 of 50 patients with glottic cancer the same phenomenon was recorded. Histology revealed in 6 of those 7 patients with clinical diagnosis of chronic chorditis invasive cancer of the vocal fold. Detailed and more sophisticated techniques (PAF Halmi for elastic and collagen fibres and neurohistochemical technique S-100 and NSE for nerve elements) demonstrated mainly preserved layer structure of vocal fold lamina propria and infiltrated nerve endings. Such histological findings strongly suggest that cancer infiltration is responsible for rapid changes of fundamental frequency (via mucosal reflexes) although vibratory segments are regular because of preserved layer structure. Such findings could contribute to better understanding of laryngeal control mechanisms and laryngeal mucosal reflexes in human. Also this acoustical sign may be a useful diagnostical parameter for very early diagnosis of glottic cancer. This is possible because of the great sensitivity and complexity of phonatory function.

Experimental study on reinnervation of vocal cord adductors with the ansa cervicalis

The purpose of this study was to reestablish the adduction of the paralyzed vocal cord through reinnervation of the adductor muscles for unilateral vocal cord paralysis. In nine dogs, the adductor branch of the recurrent laryngeal nerve was anastomosed to the main branch of the ansa cervicalis. Six months later, various techniques of observation showed that seven of nine cases had excellent to good adduction during whining. Adduction was caused by reinnervation of the adductor muscles from the ansa cervicalis as demonstrated by laryngeal spontaneous and evoked electromyography, contraction tension, and various histologic findings. Therefore, the new technique could be a good treatment of unilateral vocal cord paralysis.