Findings of Multiple Muscle Involvement in a Study of 214 Patients with Laryngeal Dystonia Using Fine-Wire Electromyography

DaxibotulinumtoxinA Treatment for Laryngeal Respiratory Dystonia

BACKGROUND

Laryngeal respiratory dystonia (LRD) is diagnosed based on clinical presentation, patient history, and physical examination. Key indicators include dyspnea, desynchronized breathing patterns, and laryngoscopic findings that reveal vocal fold adduction during inspiration. Treatment for LRD remains controversial and often yields limited effectiveness. While botulinum toxin type A (BtxA) is commonly injected into the thyroarytenoid-lateral cricothyroid (TA-LCA) muscle complex, there are cases where injections into the interarytenoid (IA) muscle have also proven beneficial. DaxibotulinumtoxinA (DAXI) is an emerging therapy that has shown promising effectiveness and safety across various conditions, including cervical dystonia. In this report, we present the first documented use of DAXI specifically for LRD, highlighting the significant benefits experienced by the patient compared to previous treatments with BtxA.

CASE

A 77-year-old man presented with a 1-year history of significant shortness of breath. Laryngeal endoscopy demonstrated inappropriate adduction of the patient's vocal folds during respiration, suggestive of LRD. The patient received their first Botox (BtxA) injection in May 2018 and has since undergone a total of 40 injections. The patient had a variable response to BtxA injection into his TA-LCA muscle complex, experiencing general improvement in breathing but frequent negative impact on voice and swallowing function. In November of 2021, electromyography-guided BtxA injection into the patient's IA muscle was performed with significant improvement in results. The patient described near-complete resolution of his LRD breathing symptoms with minimal voice changes and a duration of benefit of ~50 days. In November of 2023, DAXI injection into the patient's IA muscle was performed. The patient self-reported a complete resolution of his symptoms for a total duration of benefit of 91 days. Subsequent injections with DAXI in February and May of 2024 had near identical responses.

CONCLUSION

DAXI appears to provide ~80% better duration than the patient's average BtxA injection and a 57% improvement than his best BtxA injection. DAXI is a safe and realistic alternative to BtxA injection in patients with LRD.

Utility of maximum phonation time in the diagnosis of spasmodic dysphonia (laryngeal dystonia)

OBJECTIVES

Maximum phonation time is a simple test used to assess glottic competency. Our objective was to evaluate any correlation between maximum phonation time and spasmodic dysphonia as adductor spasmodic dysphonia and abductor spasmodic dysphonia have an adductor and abductor overdrive, respectively.

METHODS

A 3-year data-review was performed for patients diagnosed with adductor spasmodic dysphonia, abductor spasmodic dysphonia and mixed spasmodic dysphonia. Maximum phonation time was noted on the first visit and compared with a control group.

RESULTS

Average maximum phonation time in adductor spasmodic dysphonia, abductor spasmodic dysphonia and control group was 25 seconds, 9 seconds and 16 seconds. A significant difference was found for adductor spasmodic dysphonia and abductor spasmodic dysphonia. A receiver operating characteristic curve analysis between adductor spasmodic dysphonia and control groups showed a positive predictive value of 81.3 per cent, negative predictive value of 83.9 per cent, sensitivity of 79.6 per cent and specificity of 85.2 per cent. Level of evidence = 4.

CONCLUSION

We recommend that maximum phonation time be added to the diagnostic armamentarium of spasmodic dysphonia. This correlation between maximum phonation time and spasmodic dysphonia has not been previously published.

Botulinum Neurotoxin Therapy in the Clinical Management of Laryngeal Dystonia

Laryngeal dystonia (LD), or spasmodic dysphonia (SD), is a chronic, task-specific, focal movement disorder affecting the larynx. It interferes primarily with the essential functions of phonation and speech. LD affects patients' ability to communicate effectively and significantly diminishes their quality of life. Botulinum neurotoxin was first used as a therapeutic agent in the treatment of LD four decades ago and remains the standard of care for the treatment of LD. This article provides an overview of the clinical application of botulinum neurotoxin in the management of LD, focusing on the classification for this disorder, its pathophysiology, clinical assessment and diagnosis, the role of laryngeal electromyography and a summary of therapeutic injection techniques, including a comprehensive description of various procedural approaches, recommendations for injection sites and dosage considerations.

Selective stimulation of human intrinsic laryngeal muscles: Analysis in a mathematical three-dimensional space

OBJECTIVES/HYPOTHESIS

Standard stimulating methods using square waves do not appropriately restore physiological control of individual intrinsic laryngeal muscles (ILMs). To further explore our earlier study of evoked orderly recruitment by quasitrapezoidal (QT) currents, we integrated the contribution of the cricothyroideus (CT) with attention to mutual activation in an additional patient, based on recent studies of appropriate responses via strict recurrent laryngeal nerve (RLN) stimulation.

STUDY DESIGN

Basic science study.

METHODS

The patient received functional electrical stimulation (FES) with QT pulses at 5 Hz, 60 to 2,000 μAmp, 100 to 500 μs pulse width, 0 to 500 μs decay. Ipsilateral electromyography (EMG) responses were calculated using the average maximum amplitude, area under the curve, and the root mean square of the rectified amplitude waveforms. The thyroarytenoideus (TA), posterior cricoarytenoideus (PCA), lateral cricothyroideus (LCA), and the CT were each interrogated via two monopolar electrodes, values were recorded in MATLAB, exported to Excel, and analyzed. Individual and mutual recruitment configurations and activation delays with stimulation were explored using multiple regression and exploration factor analyses.

RESULTS

A total of 868 EMG data points based on 18 trials and up to 11 subtrials were captured from each of the four ILMs. Various combinations of pulse amplitude, pulse width, and exponential decay were found to produce significant (P ≤ .001) individual ILM responses. CT mirrored the LCA, whereas the TA and PCA exhibited separate interactions along shared trajectories in a three-dimensional space.

CONCLUSIONS

FES calibrated to individual and coupled ILMs offers promise for restoring normal and pathological contraction patterns via strict RLN stimulation.

LEVEL OF EVIDENCE

5 Laryngoscope, 130:967-973, 2020.

Phenomenology, genetics, and CNS network abnormalities in laryngeal dystonia: A 30-year experience

OBJECTIVE

Laryngeal dystonia (LD) is a functionally specific disorder of the afferent-efferent motor coordination system producing action-induced muscle contraction with a varied phenomenology. This report of long-term studies aims to review and better define the phenomenology and central nervous system abnormalities of this disorder and improve diagnosis and treatment.

METHODS

Our studies categorized over 1,400 patients diagnosed with LD over the past 33 years, including demographic and medical history records and their phenomenological presentations. Patients were grouped on clinical phenotype (adductor or abductor) and genotype (sporadic and familial) and with DNA analysis and functional magnetic resonance imaging (fMRI) to investigate brain organization differences and characterize neural markers for genotype/phenotype categorization. A number of patients with alcohol-sensitive dystonia were also studied.

RESULTS

A spectrum of LD phenomena evolved: adductor, abductor, mixed, singer's, dystonic tremor, and adductor respiratory dystonia. Patients were genetically screened for DYT (dystonia) 1, DYT4, DYT6, and DYT25 (GNAL)-and several were positive. The functional MRI studies showed distinct alterations within the sensorimotor network, and the LD patients with a family history had distinct cortical and cerebellar abnormalities. A linear discriminant analysis of fMRI findings showed a 71% accuracy in characterizing LD from normal and in characterizing adductor from abductor forms.

CONCLUSION

Continuous studies of LD patients over 30 years has led to an improved understanding of the phenomenological characteristics of this neurological disorder. Genetic and fMRI studies have better characterized the disorder and raise the possibility of making objective rather than subjective diagnoses, potentially leading to new therapeutic approaches. Laryngoscope, 128:S1-S9, 2018.

Chemodenervation of the Larynx

Botulinum neurotoxin (BoNT) has existed for thousands of years; however, it was not medically utilized until investigations into its therapeutic use began in sincerity during the late 1970s and 1980s. This, coupled with the reclassification of spasmodic dysphonia as a focal dystonia, led to the use of chemodenervation for this disorder, which has since become a refined technique. Indeed, due to its safety and efficacy, BoNT has been investigated in multiple neurolaryngology disorders, including spasmodic dysphonia, vocal tremor, and muscle tension dysphonia. BoNT has been shown to be a useful and safe adjunct in the treatment for these disorders and may reduce or eliminate oral pharmacotherapy and/or prevent the need for a surgical intervention. We present the historical background, development, proposed mechanisms of action, uses, and techniques for administering BoNT for laryngeal disorders, with a particular focus on spasmodic dysphonia.

Long-Term Botulinum Toxin Dose Consistency for Treatment of Adductor Spasmodic Dysphonia

Objectives:

Botulinum toxin (BTX) injection is currently the primary and most common treatment for adductor spasmodic dysphonia (ADSD). A variety of injection strategies and dosage regimens have been described. This study reports on our experience with the dosage schedule and dosing consistency of BTX for the treatment of ADSD.

Methods:

We retrospectively reviewed our laryngeal BTX database for the period 1991 to 2005. Our strict inclusion requirements limited our selection to 13 patients who had received a minimum of 6 injections (average, 11.5; range, 6 to 19) of BTX for ADSD.

Results:

The average total dose of BTX to the larynx for each treatment episode was 3.9 units (range, 1.5 to 7.5). The total dose administered tended to trend downward among patients who began treatment from 1991 to 1998, indicating that the initial dose (usually 2.5 units per side) may have been high. Those patients who began from 1999 onward had a more stable dose, indicating that the initial dose (usually 1.5 units per side) was more suitable. The subjects underwent an average of 2.2 injections (range, 1 to 5) before reaching their optimal BTX dose. The total number of treatments performed in this group of patients was 150, of which 145 were successful (96.7%).

Conclusions:

The BTX dose for the optimal treatment of ADSD usually remains consistent over time, as does the treatment interval. An initial dose of 1.5 units per side or less appears to improve dosing stability, indicating that the initial dosing of 2.5 units per side in our study was often greater than required. The optimal BTX dose was usually ascertained by the second or third injection. In our patient population, the long-term dosing consistency of BTX confirmed that neither tachyphylaxis nor increasing sensitivity to BTX occurred during the course of treatment for ADSD.

Refractory Dysphonia Due to Isolated Cricothyroid Muscle Dystonia

OBJECTIVE

To demonstrate the utility of electromyography (EMG) in the evaluation and management of treatment-resistant dysphonia.

METHOD

We report a case of refractory dysphonia in which EMG was used to identify and treat isolated cricothyroid (CT) dystonia.

RESULTS

The patient, a healthy 43-year-old woman, presented with 9 months of progressive hoarseness. Her symptoms were present across vocal tasks but were particularly bothersome while dictating. On presentation, her voice was rated grade 3, roughness 3, breathiness 1, asthenia 0, and strain 3 (G3R3B1A0S3). Videostroboscopy was remarkable for hyperfunction. Voice therapy was not beneficial despite appropriate effort. Microdirect laryngoscopy revealed no evidence of structural pathology. The patient was referred for EMG because of her normal examination and failure to improve with therapy. The CT muscle demonstrated an increased latency of 750 ms in all vocal tasks. One month after CT injection with 3 units of botulinum toxin (BTX), her voice was improved. Perceptual voice evaluation was rated G1R1B0A0S1. Voice Handicap Index improved from 87 to 35.

CONCLUSIONS

In the absence of structural pathology, EMG can be a useful adjunct in the diagnosis of dysphonia that persists despite adequate trials of voice therapy. To our knowledge, this is the only report of laryngeal dystonia due to isolated CT dysfunction successfully treated with BTX.

Value of Laryngeal Electromyography in Spasmodic Dysphonia Diagnosis and Therapy

OBJECTIVE

To investigate the role of laryngeal electromyography (LEMG) in the diagnosis and treatment of spasmodic dysphonia (SD).

METHODS

The clinical manifestations, characteristics of motor unit potentials (MUPs), recruitment potentials, and laryngeal nerve evoked potentials (EPs) in LEMG, as well as the changes after botulinum toxin (BTX) treatment, were analyzed in 39 patients with adductor SD.

RESULTS

The main clinical manifestations were a strained voice and phonation interruptions; in addition, the patients displayed hyper-adducted vocal folds during phonation. LEMG revealed significantly increased amplitudes of the thyroarytenoid muscle MUPs. The recruitment potentials were in a dense bunch, discharging full interference patterns with significantly increased amplitudes; the mean and maximum amplitude of recruitment potentials were 3090 μV and 5000 μV, respectively. The amplitude of EPs of thyroarytenoid muscle increased significantly; the mean and maximum amplitudes were 10.3 mV and 26.3 mV, respectively. After BTX was injected, the LEMG revealed denervation changes, and the EPs weakened or disappeared in the injected muscle.

CONCLUSIONS

SD could be diagnosed, and the therapeutic efficacy of SD treatments could be evaluated based on clinical characteristics combined with LEMG characteristics. The increased amplitudes of the recruitment potentials and EPs of the thyroarytenoid muscle were the characteristic indexes. After BTX was injected, denervated potential characteristics appeared in the muscles.

Spasmodic dysphonia: a seven-year audit of dose titration and demographics in the Indian population

Objectives:

This study aimed to evaluate the demographics of spasmodic dysphonia in the Indian population and to analyse the optimum dose titration of botulinum toxin type A in this group. A comparative analysis with international studies was also performed.

Method:

The study involved a retrospective analysis and audit of botulinum toxin type A dose titration in spasmodic dysphonia patients who visited our voice clinic between January 2005 and January 2012.

Results:

The average total therapeutic dose required for patients with adductor spasmodic dysphonia was 4.2 U per patient per vocal fold (total 8.4 U per patient), and for patients with abductor spasmodic dysphonia, it was 4.6 U per patient.

Conclusion:

Our audit revealed that 80 per cent of the spasmodic dysphonia patients were male, which contrasts dramatically with international studies, wherein around 80 per cent of spasmodic dysphonia patients were female. Our study also revealed a higher dose titration of botulinum toxin for the Indian spasmodic dysphonia population in both adductor and abductor spasmodic dysphonia cases.

Differential vibratory characteristics of adductor spasmodic dysphonia and muscle tension dysphonia on high-speed digital imaging

OBJECTIVES

The purpose of this study was to quantify disorder-specific signature kinematic disturbances of vibratory motion in adductor spasmodic dysphonia (AdSD) and muscle tension dysphonia (MTD), in voice disturbances of a severe nature, with the use of high-speed digital imaging (HSDI). A secondary hypothesis of the study was to investigate the sensitivity and specificity of the signature kinematic features obtained from HSDI, in differentiating between AdSD and MTD.

METHODS

We used vibratory features from automated extraction of vocal fold motion waveforms and glottal cycle montage analysis from HSDI for differential kinematic profiling of AdSD and MTD.

RESULTS

Novel features of motion irregularities and micromotions (as small as 27 ms) were greater in number for AdSD, whereas reduced motion irregularities, absence of oscillatory breaks, absence of micromotions, and increased hyperfunction characterized the MTD group. Oscillatory breaks (as small as 8 ms), although present only in the AdSD group, were not statistically significant because of their reduced number of occurrences compared to the other features. Further montage analysis of successive glottal cycles of oscillatory breaks in the AdSD group revealed 3 different kinematic patterns within the AdSD group, indicative of likely AdSD with: 1) possible predominant thyroarytenoid muscle involvement, 2) possible predominant cricothyroid muscle involvement, and 3) possible combined involvements of the thyroarytenoid and lateral cricoarytenoid muscles. Four consistent but unique kinematic patterns were identified within the MTD group: 1) diplophonia, 2) vocal fry, 3) breathy phonation, and 4) pressed phonation. Sensitivity and specificity analysis revealed that only motion irregularity was a significant predictor of the presence of AdSD.

CONCLUSIONS

Fine kinematic analysis from HSDI can be used to aid detailed clinical profiling of the source characteristics of AdSD and MTD.

Differentiating between adductor and abductor spasmodic dysphonia using airflow interruption

OBJECTIVES/HYPOTHESIS

To measure the laryngeal resistance (R(L)), subglottal pressure (P(s)), and mean flow rate (MFR) of adductor (ADSD) and abductor (ABSD) spasmodic dysphonia patients using the airflow interrupter.

METHODS

The R(L) of six ABSD and seven ADSD patients was measured using the airflow interrupter, a noninvasive device designed to measure MFR and P(s) via mechanical balloon valve interruption. Subjects performed 10 trials at each of two intensity levels, with each trial consisting of a sustained /a/ during which phonation was interrupted for 500 ms. Laryngeal resistance was calculated as subglottal pressure divided by airflow.

RESULTS

Mean R(L) for the ADSD and ABSD subtypes at 65 dB were 24.78 cmH(2)O/L/s and 14.51 cmH(2)O/L/s, respectively (P = .04). Mean R(L) at 70 dB were 40.02 cmH(2)O/L/s and 15.84 cmH(2)O/L/s (P = .014). P(s) for the ADSD and ABSD subtypes at 65 dB were 10.23 cmH(2)O and 8.32 cmH(2)O, respectively (P = .582). At the 70 dB level, P(s) were 12.39 cmH(2)O and 11.78 cmH(2)O (P = .886). MFR for the ADSD and ABSD subtypes at 65 dB were 435 mL/s and 746 mL/s (P = .205). Mean MFR at 70 dB were 518 mL/s and 848 mL/s (P = .198).

CONCLUSIONS

Noninvasive measurements of R(L) may be useful for differentiating between ADSD and ABSD. This simple objective test, which produces a quantitative output, could be used to evaluate laryngeal function in patients with spasmodic dysphonia.

Interarytenoid muscle botox injection for treatment of adductor spasmodic dysphonia with vocal tremor

OBJECTIVES/HYPOTHESIS

Up to one-third of patients presenting with adductor spasmodic dysphonia will have an associated vocal tremor. These patients may not respond fully to treatment using thyroarytenoid (TA) muscle botulinum toxin (Botox) injection. Treatment failures are attributed to the involvement of multiple muscle groups in the tremor. This study evaluates the results of combined interarytenoid (IA) and TA muscle Botox injection in a group of 27 patients with adductor spasmodic dysphonia and vocal tremor and in four patients with severe vocal tremor alone.

STUDY DESIGN

Patient-satisfaction data were reviewed retrospectively. Pre- and postinjection acoustic data were collected prospectively.

METHODS

Acoustic measures of fundamental frequency and cycle-by-cycle variability in frequency (jitter) and intensity (shimmer) were obtained from 15 patients' sustained vowel productions. Measures were collected after TA muscle injection, alone, and after combined TA and IA (TA+IA) muscle injections. In addition, two experienced voice clinicians blindly assessed tremor severity from recordings made for each patient in the two conditions. Patients were also queried regarding their satisfaction with the results of the injections and whether they desired to continue receiving TA+IA treatment.

RESULTS

Significant improvement in all acoustic measures except for % jitter was observed after the TA+IA muscle injections. Listeners identified voice samples after TA+IA muscle injections as demonstrating less tremor in 73% of the paired comparisons. Sixty-seven percent of the patients with spasmodic dysphonia and vocal tremor wished to continue to receive IA muscle injections. Only one patient with severe vocal tremor wished to continue with injections.

CONCLUSIONS

The addition of an IA muscle Botox injection to the treatment of patients with a combination adductor spasmodic dysphonia and vocal tremor may improve voice outcomes.

Recommendations of the Neurolaryngology Study Group on laryngeal electromyography

The Neurolaryngology Study Group convened a multidisciplinary panel of experts in neuromuscular physiology, electromyography, physical medicine and rehabilitation, neurology, and laryngology to meet with interested members from the American Academy of Otolaryngology Head and Neck Surgery, the Neurolaryngology Subcommittee and the Neurolaryngology Study Group to address the use of laryngeal electromyography (LEMG) for electrodiagnosis of laryngeal disorders. The panel addressed the use of LEMG for: 1) diagnosis of vocal fold paresis, 2) best practice application of equipment and techniques for LEMG, 3) estimation of time of injury and prediction of recovery of neural injuries, 4) diagnosis of neuromuscular diseases of the laryngeal muscles, and, 5) differentiation between central nervous system and behaviorally based laryngeal disorders. The panel also addressed establishing standardized techniques and methods for future assessment of LEMG sensitivity, specificity and reliability for identification, assessment and prognosis of neurolaryngeal disorders. Previously an evidence-based review of the clinical utility of LEMG published in 2004 only found evidence supported that LEMG was possibly useful for guiding injections of botulinum toxin into the laryngeal muscles. An updated traditional/narrative literature review and expert opinions were used to direct discussion and format conclusions. In current clinical practice, LEMG is a qualitative and not a quantitative examination. Specific recommendations were made to standardize electrode types, muscles to be sampled, sampling techniques, and reporting requirements. Prospective studies are needed to determine the clinical utility of LEMG. Use of the standardized methods and reporting will support future studies correlating electro-diagnostic findings with voice and upper airway function.

Estimation of the number and size of motor units in intrinsic laryngeal muscles using morphometric methods

The number and size of motor units in the intrinsic laryngeal muscles were estimated by morphometric methods. Laryngeal muscles with their respective nerve branches were obtained from 64 fresh cadavers (32 older than 60 years, mean age 74 +/- 9 years and 32 younger than 60 years, mean age 51 +/- 8 years). Myelinated nerve fibers and the total number of muscle fibers were counted. Motor unit size was estimated by dividing the total number of muscle fibers by the total number of motor units in each case. The mean number of motor units ranged from 268 +/- 1.3 (interarytenoid muscle) to 431 +/- 1.6 (cricothyroid muscle). Thyroarytenoid and cricothyroid muscle presented the smallest (9.8 +/- 0.2) and largest (20.5 +/- 0.9) motor unit size, respectively, suggesting that thyroarytenoid muscle has a greater capacity to fine-tune its total force compared with the other intrinsic laryngeal muscles. No differences in motor unit number or size were observed between the right and left sides or between younger and older subjects. It is suggested that synaptic rearrangements may occur at the level of the neuromuscular junction in the human larynx that may explain the age-related changes in motor units reported by clinical methods.

Botulinum toxin therapy of laryngeal muscle hyperactivity syndromes: comparing different botulinum toxin preparations

Spasmodic dysphonia (SD) is a focal dystonia characterized by a strained, strangled voice. Botulinum toxin is a symptomatic treatment for SD and has become the mainstay of therapy over the last two decades. In this manuscript, we briefly review different laryngeal muscle hyperactivity syndromes, their injection techniques and toxins currently available. Adductor SD is the most common indication for botulinum toxin treatment in the larynx. All studies report similar results with regard to improvement, patient satisfaction and side effects. We describe different injection techniques to treat this disorder such as the percutaneous, transoral, transnasal, point-touch techniques. In abductor SD, a subtype of SD, the treatment is aimed at the posterior cricoarytenoid muscle. Other applications of botulinum toxin in the larynx include spasmodic laryngeal dyspnea and voice tremors. We also review injection techniques, the different toxin types used, and toxin doses.

Long-Term Follow-Up Results of Selective Laryngeal Adductor Denervation-Reinnervation Surgery for Adductor Spasmodic Dysphonia

Selective laryngeal adductor denervation-reinnervation surgery for the treatment of adductor spasmodic dysphonia was reported in 1999 in 21 patients with encouraging results. Here, we report long-term results of this procedure. Surgical outcome was evaluated using patient surveys and perceptual voice assessment. Measured outcomes included Voice Handicap Index (VHI)-10 scores, patient questionnaire, and perceptual evaluation for voice breaks and breathiness. Patient survey was obtained from 83 patients, and perceptual voice evaluation was performed in voice samples from 46 patients. Average follow-up interval was 49 months. Mean VHI-10 scores improved from a mean of 35.6 to 12.7. Eighty-three percent showed significantly improved VHI-10 scores, representing improved physical, social, and emotional well-being. There was a high degree of patient satisfaction, with 91% agreeing that their voice is more fluent after the surgery. Perceptual evaluation of postoperative voice samples revealed voice breaks in 26% (15% mild, 4% moderate, 7% severe) and breathiness in 30% (11% mild, 13% moderate, 6% severe). A majority of patients had stable, long-lasting resolution of spasmodic voice breaks.

Treatment of adductor-type spasmodic dysphonia by surgical myectomy: a preliminary report

OBJECTIVES

Despite the belief that it represents a central neurologic dysfunctional process, adductor-type spasmodic dysphonia without tremor is usually effectively treated by injection of botulinum toxin A; however, in most cases such injections must be repeated every few months. A promising new surgical procedure is herein reported.

METHODS

Under local anesthesia with intravenous sedation, a large laryngoplasty window is created, and under direct vision with intraoperative voice monitoring, fibers from the thyroarytenoid and lateral cricoarytenoid muscles are removed until breathiness occurs. The two sides are staged; that is, one side is done at a time, with surgery on the second side being performed 3 to 6 months after that on the first side, if needed.

RESULTS

This was a retrospective, unblinded study of 5 patients who underwent myectomy of the thyroarytenoid and lateral cricoarytenoid muscles. The preliminary results show improved voice fluency in all patients at 5 to 19 months of follow-up. There was no period of prolonged breathiness or dysphagia in any of the patients, and there were no surgical complications.

CONCLUSIONS

Myectomy of the thyroarytenoid and lateral cricoarytenoid muscles is a promising new surgical treatment for adductor-type spasmodic dysphonia that may effectively mimic "permanent" botulinum toxin injections.

Singer's dystonia: first report of a variant of spasmodic dysphonia

OBJECTIVES

We discuss the phonatory characteristics of a previously undescribed focal laryngeal dystonia present in the singing voice.

METHODS

We performed a retrospective chart review of 5 patients with singer's dystonia at a neurolaryngology referral center.

RESULTS

Four patients reviewed demonstrated phonatory characteristics consistent with adductor spasmodic dysphonia present in their singing voice. One patient demonstrated abductor spasmodic dysphonia in the singing voice. Each patient initially exhibited normal connected speech in conversational voicing. The treatment protocol and outcome are discussed, including the use of botulinum toxin.

CONCLUSIONS

Singer's dystonia is a previously undescribed neurologic disorder that should be understood by those who treat voice performers and voice disorders.

Three-dimensional compartmentalization of myosin heavy chain and myosin light chain isoforms in dog thyroarytenoid muscle

The thyroarytenoid muscle, a vocal fold adductor, has important roles in airway protection (e.g., prevention of aspiration) and phonation. Isoform expression of myosin heavy chain (MHC), a major determinant of muscle-shortening velocity, has been reported to be heterogeneous in this muscle in several mammals, differing markedly between the medial and lateral divisions. The objective was to determine the isoform expression patterns of both MHC and myosin light chain (MLC), with the latter having a modulatory role in determining shortening velocity, to further test whether the expression of both myosin subunits differs in multiple specific sites within the divisions of the dog thyroarytenoid muscle, potentially revealing even greater compartmentalization in this muscle. Our results indicate the existence of large gradients in the relative levels of individual MHC isoforms in the craniocaudal axis along the medial layer (i.e., airflow axis), where levels of MHC-I and MHC-IIA are low at both ends of the axis and high in the middle and MHC-IIB has a reciprocal distribution. The lateral layer is more uniform, with high levels of MHC-IIB throughout. The level of MHC-IID is relatively constant along the axis in both layers. Large differences exist in the distribution of MHC isoforms among single fibers isolated from sites along the craniocaudal axis, especially in the lateral layer. Systematic regional variations are apparent in the MLC isoform composition of single fibers as well, including some MLC isoform combinations that are not observed in dog limb muscles. Variations of MHC and MLC isoform expression in the dog thyroarytenoid muscle are greater than previously recognized and suggest an even broader range of contractile properties within this multifunctional muscle.