Recommendations of the Neurolaryngology Study Group on laryngeal electromyography

Current opinion on laryngeal electromyography

PURPOSE

This study evaluates expert opinion on laryngeal electromyography (LEMG).

METHODS

A cross-sectional design was used to conduct an online survey of LEMG experts in 2021. They were questioned about the number LEMG performed annually, type of electrodes used, sector worked in, pain during the test, placement of the needle electrodes, interpretation of electrical muscle parameters, diagnosis of neuromuscular injury, prognostic sensitivity in vocal fold paralysis (VFP), laryngeal dystonia, tremor and synkinesis and quantifying LEMG.

RESULTS

Thirty-seven professionals answered (23 Spanish and 14 from other countries), with a response rate of 21.56%. All physicians used LEMG. 91.9% had one- or two-years' experience and 56.8% performed 10-40 LEMG per year. 70.3% were otolaryngologists and 27%, neurologists. In 89.1% of cases, a team of electrodiagnostic physician and otolaryngologist performed LEMG. 91.3% of Spanish respondents worked in Public Health, 7.14% of other nationalities; 37.8% in a university department. Bipolar concentric needles electrodes were used by 45.9% and monopolar concentric by 40.5%. 57% professionals considered good patients' tolerance to the test. LEMG sensitivity was regarded as strong, median and interquartile range were 80.0 [60.0;90.0] to diagnose peripheral nerve injuries, less for other levels of lesions, and strong to evaluate prognosis, 70.0 [50.0;80.0]. Respondents believe locate the thyroarytenoid and the cricothyroid muscles with the needle, 80.0 [70.0;90.0], as opposed to 20.0 [0.00;60.0] the posterior cricoarytenoid. The interpretation of the electrical parts of the LEMG was strong, 80.0 [60.0;90.0]. LEMG identify movements disorders, 60.0 [20.0;80.0], and synkinesis, 70.0 [30.0;80.0]. The professionals prefer quantitative LEMG, 90.0 [60.0;90.0].

CONCLUSIONS

The experts surveyed consider LEMG that is well tolerated by patients. The insertional and spontaneous activity, recruitment and waveform morphology can be assessed easily. LEMG is mainly useful in the study of peripheral nerve injuries, and its value in VFP prognosis is considered strong.

Hemodynamic Changes Associated With Transcervical Laryngeal Injection of Botulinum Toxin

PURPOSE

Laryngeal dystonia is a chronic neurologic disorder characterized by intention-induced spasms of the vocal folds driven by aberrant central motor processing. The use of in-office transcervical botulinum toxin injection for the treatment of laryngeal disorders, such as laryngeal dystonia, has been deemed safe and efficacious. There is, however, no available data outlining the hemodynamic changes experienced by patients undergoing this frequently performed procedure.

METHODS

One hundred and one patients diagnosed with laryngeal dystonia were enrolled in this prospective study. These patients underwent transcervical laryngeal botulinum toxin injection to address their dysphonia. Vital signs where acquired prior to, and at the time of injection. Alterations in these parameters were then evaluated for statistical significance.

RESULTS

Statistically significant increases in mean heart rate (5.8 ± 10.8 bpm, P < 0.0001), systolic blood pressure and diastolic blood pressure (7.0 ± 9.5 mm Hg, P < 0.0001; 8.7 ± 14.7 mm Hg, P < 0.0001) were discovered. No statistically significant difference in oxygen saturation was noted and no patients in the study faced major adverse outcomes.

CONCLUSIONS

Though these findings may not have related to clinically significant complication, our study demonstrates the importance of understanding potential stressors in a procedure routinely performed by laryngologists. This may result in more careful patient selection, alterations in procedure, and improved safety by acting in a timely fashion if alarming changes in hemodynamic parameters are noted.

Laryngeal Electromyography in the Therapeutic Process of Patients with Vocal Fold Immobility or Dysmobility

(1) Background: Laryngeal electromyography (LEMG) plays a key role in classifying the severity of nerve damage and determining the prognosis of the nerve recovery. LEMG is primarily a qualitative study, without a standardized approach to interpretation. The development of qualitative and quantitative analysis would situate LEMG in the gold standard of modern neurolaryngologic diagnostics. The aim of this study was to quantitatively evaluate laryngeal electromyography recorded in patients with vocal fold immobility or dysmobility. (2) Methods: The electromyographic material comprised 84 thyroarytenoid muscles recordings of 42 patients. (3) Results: In our study, we observed significant differences between EMG characteristics of healthy and paralyzed VF. Our study showed that recording laryngeal muscle activity during successive phases of breathing provides additional valuable information. We noticed that the frequency and amplitude of motor unit potentials correlates with the return of vocal fold functionality. (4) Conclusions: Laryngeal EMG guides the clinician on the best course of treatment for the patient. It is therefore important to develop an effective methodology and consensus on the quantitative interpretation of the record. Amplitude and frequency parameters are valuable in predicting neural recovery and in the return of vocal fold mobility.

Vocal fold immobility with normal LEMG: A range of possibilities

OBJECTIVE

The objective of this paper is to study the etiology of vocal fold immobility with non-pathological LEMG.

METHODS

A retrospective study was performed on patients who presented with vocal fold immobility and underwent LEMG from 2009 to 2017. Those patients with normal LEMG findings were selected. The different causes of vocal fold impairment were studied.

RESULTS

Of the 120 patients included in this study, 15 had a normal LEMG recording. The different etiologies of vocal fold immobility were idiopathic, central nervous system damage, iatrogenic, and external compression.

CONCLUSIONS

Vocal fold immobility and vocal fold paralysis are not equal terms. Vocal fold immobility with normal LEMG has a heterogeneous group of causes. It is not correct to assume that the major cause of immobility in patients with normal LEMG is always cricoarytenoid joint fixation.

Evaluation of Laryngeal Motor Neuropathy Using Transcranial Magnetic Stimulation-Mediated Evoked Potentials

OBJECTIVES/HYPOTHESIS

Contemporary evaluation of vocal fold motion impairment largely relies on clinical laryngoscopy, with the diagnoses of vocal fold paresis (VFPa) and paralysis (VFP) being based on identification of partial and complete restriction of gross vocal fold motion, respectively. No consensus exists on the diagnostic criteria of VFPa. Laryngeal electromyography does not offer any insight into nerve conduction velocity without the adjunction of nerve conduction studies, which are impractical to perform on laryngeal nerves due to their anatomic location. The present study aims to assess the feasibility of laryngeal nerve conduction studies using transcranial magnetic stimulation (TMS)-mediated myogenic evoked potentials in the evaluation of laryngeal motor nerve function.

STUDY DESIGN

Prospective controlled cohort study.

METHODS

Enrollment of three groups of subjects defined as healthy volunteers, subjects with clinically diagnosed unilateral VFP, and subjects with clinically diagnosed unilateral VFPa of peripheral etiology. Electrodiagnostic studies consisting of bilateral stimulation of the laryngeal motor cortex, proximal cisternal, and peripheral portions of the vagus nerves were performed using figure-of-eight magnetic stimulation coils, and myogenic evoked potentials recorded from bilateral thyroarytenoid, cricothyroid, and posterior cricoarytenoid muscles using indwelling hook wire electrodes. Conduction latencies were plotted against demographic and anthropometric variables. Values obtained in healthy volunteers were used as normative references and compared to aggregated latencies of VFP and VFPa groups.

RESULTS

Enrolled subjects included 19 healthy volunteers, 5 subjects with VFP, and 4 subjects with VFPa. Normative laryngeal nerve conduction latency ranges measured in healthy subjects were comparable to prior published values, and recorded latencies increased in positive correlation with age. VFPa subjects exhibited increased latencies in affected nerve sites, while VFP subjects presented more variability in electrophysiologic manifestations, mostly dependent on their degree of compensatory reinnervation. Aberrant and synkinetic reinnervation patterns were more predominant in the VFP group than the VFPa group.

CONCLUSIONS

Laryngeal nerve conduction studies using TMS-mediated myogenic evoked potentials are safely feasible. They may serve as a useful complement to laryngeal electromyography in the evaluation of motor laryngeal neuropathy and represent a promising diagnostic modality in the evaluation of VFPa. Based on the present study's findings, the commonly accepted notion of VFPa as a manifestation of a less severe form of neuropathy than VFP may be unsubstantiated. Aging may contribute to progressive motor nerve dysfunction. Future investigations are needed to ascertain the role of nerve conduction studies in clinical laryngology practice.

LEVEL OF EVIDENCE

3 Laryngoscope, 2022.

Vocal fold immobility with normal LEMG: A range of possibilities

OBJECTIVE

The objective of this paper is to study the etiology of vocal fold immobility with non-pathological LEMG.

METHODS

A retrospective study was performed on patients who presented with vocal fold immobility and underwent LEMG from 2009 to 2017. Those patients with normal LEMG findings were selected. The different causes of vocal fold impairment were studied.

RESULTS

Of the 120 patients included in this study, 15 had a normal LEMG recording. The different etiologies of vocal fold immobility were idiopathic, central nervous system damage, iatrogenic, and external compression.

CONCLUSIONS

Vocal fold immobility and vocal fold paralysis are not equal terms. Vocal fold immobility with normal LEMG has a heterogeneous group of causes. It is not correct to assume that the major cause of immobility in patients with normal LEMG is always cricoarytenoid joint fixation.

[Neurolaryngology]

Neurological and neurophysiological knowledge of neuromuscular diseases is combined in neurolaryngology with experience from laryngology. Laryngeal electromyography (LEMG) is the most important diagnostic and prognostic tool in neurolaryngology. It can be combined with diagnostic electrostimulation. Interest in LEMG today extends beyond the thyroarytenoid muscle to all accessible laryngeal muscles. LEMG should be performed and interpreted according to a standardized protocol. Main applications of LEMG are confirmation, topodiagnostic and prognostic assessment of vocal fold paralysis. It is possible to differentiate fresh from old recurrent laryngeal nerve lesions as well as mechanical vocal fold fixations from paralysis. Needle guidance for botulinum toxin injections in spasmodic dysphonia and for augmentation laryngoplasty can be supported by LEMG, but also by laryngeal ultrasound. The timing of therapy for temporary and permanent augmentations, thyroplasty and reinnervation surgery may be better defined with experience from neurolaryngology. The use of diagnostic neurostimulation can reveal any remaining active movement potential of a vocal fold and thus help identify candidates for future laryngeal pacemaker treatments. Other topics in neurolaryngology include spasmodic dysphonia and underlying neurological diseases such as stroke, central vocal fold paralysis, essential tremor and Parkinson's disease. Laryngoscopic, clinical and LEMG characteristics of these diseases are presented.

Critical Review and Consensus Statement for Neural Monitoring in Otolaryngologic Head, Neck, and Endocrine Surgery

BACKGROUND

Enhancing patient outcomes in an array of surgical procedures in the head and neck requires the maintenance of complex regional functions through the protection of cranial nerve integrity. This review and consensus statement cover the scope of cranial nerve monitoring of all cranial nerves that are of practical importance in head, neck, and endocrine surgery except for cranial nerves VII and VIII within the temporal bone. Complete and applied understanding of neurophysiologic principles facilitates the surgeon's ability to monitor the at-risk nerve.

METHODS

The American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) identified the need for a consensus statement on cranial nerve monitoring. An AAO-HNS task force was created through soliciting experts on the subject. Relevant domains were identified, including residency education, neurophysiology, application, and various techniques for monitoring pertinent cranial nerves. A document was generated to incorporate and consolidate these domains. The panel used a modified Delphi method for consensus generation.

RESULTS

Consensus was achieved in the domains of education needs and anesthesia considerations, as well as setup, troubleshooting, and documentation. Specific cranial nerve monitoring was evaluated and reached consensus for all cranial nerves in statement 4 with the exception of the spinal accessory nerve. Although the spinal accessory nerve's value can never be marginalized, the task force did not feel that the existing literature was as robust to support a recommendation of routine monitoring of this nerve. In contrast, there is robust supporting literature cited and consensus for routine monitoring in certain procedures, such as thyroid surgery, to optimize patient outcomes.

CONCLUSIONS

The AAO-HNS Cranial Nerve Monitoring Task Force has provided a state-of-the-art review in neural monitoring in otolaryngologic head, neck, and endocrine surgery. The evidence-based review was complemented by consensus statements utilizing a modified Delphi method to prioritize key statements to enhance patient outcomes in an array of surgical procedures in the head and neck. A precise definition of what actually constitutes intraoperative nerve monitoring and its benefits have been provided.

Quantitative laryngeal electromyography (LEMG) in unilateral vocal fold paralysis: Developing normative values using the opposite normal mobile vocal fold

OBJECTIVE

Laryngeal electromyography (LEMG) is used to confirm neuropathy; traditionally, it is evaluated qualitatively. This study aimed to develop normative values for the thyroarytenoid-lateral cricoarytenoid (TA-LCA) muscle complex by determining the mean turns (MT) and mean amplitudes (MA) using the opposite normal mobile vocal fold in unilateral vocal fold paralysis (VFP). This study also compared the MT and MA of the paralyzed vocal fold with that of the normal side and analyzed their correlations.

METHODS

This is a cross-sectional study in which 77 patients (18 males, 59 females, mean age of 48) with unilateral VFP with an opposite normal mobile vocal fold underwent LEMG with a standardized protocol. Koufman gradings and MT and MA were used for the qualitative and quantitative evaluations. Mann-Whitney U test was performed to compare the median of the turns and amplitudes between the opposite normal mobile vocal fold and the paralyzed side. A linear-scale graphical "cloud" of the normal TA-LCA muscle complex was generated using logarithmic regression analysis. The qualitative and quantitative parameters were analyzed using multiple analysis of variance and Kruskall-Wallis test. Post-hoc analysis was performed to further determine the differences of the significance between both parameters. The correlation between the qualitative and quantitative parameters was analyzed using Spearman correlation.

RESULTS

The MT and MA were significantly higher for the normal TA-LCA muscle complex than the paralyzed side (582 vs. 336; 412 vs. 296, respectively) and the median of the turns and amplitudes were significantly lower in the paralyzed side with p-values <0.001. A significant difference was observed between the Koufman grading and the combination of MT and MA [F (8,144) = 73.254] and between the Koufman grading and MT and MA individually [H (4, 72) = 18.3 and H (4, 72) =33.4], in which both had p-values <0.001. A moderate negative linear relationship was seen between the Koufman grading and MT and MA. On further analysis, it was revealed that only certain pairs of Koufman grading were statistical significant.

CONCLUSIONS

This study was the first to present the quantitative normative values and "cloud" of the TA-LCA muscle complex using the opposite normal mobile vocal fold in patients with unilateral VFP in which it is comparable to healthy controls. We concluded that quantitative LEMG supports the qualitative Koufman grading method however it cannot be used independently to determine the severity of neuropathy.

Quantitative laryngeal electromyography parameters may correlate with improved outcomes following botulinum toxin injection for spasmodic dysphonia

BACKGROUND

Despite use of qualitative laryngeal electromyography (LEMG) guided botulinum toxin A (BoNT-A) injection for treatment of adductor spasmodic dysphonia (AdSD), unsatisfactory injections and complete "misses" remain problematic. We aimed to determine if the quantitative LEMG measure of number of small segments (NSS) correlates with voice outcomes following (BoNT-A injection for AdSD.

METHODS

Automated quantitative LEMG analysis was performed during electromyography (EMG) -guided BoNT-A injection into the thyroarytenoid-lateral cricoarytenoid muscle complex for treatment of AdSD. Pre-injection phonatory NSS values were correlated with clinical voice outcomes and patient reported injection results.

RESULTS

Quantitative LEMG measures were obtained for 45 AdSD patients (28 female, mean age 60.8 ± 12.8 years) during EMG-guided BoNT-A injection. Mean sampled NSS during phonation immediately prior to BoNT-A injection was 524 ± 323 (range: 2-904). Mean follow up was 36.5 ± 9.4 days; one patient was lost to follow-up. In comparison to their previous BoNT-A injection, the current injection was rated as worse, same, and better by 13 (29.5%), 25 (56.8%), and 6 (13.6%) patients, respectively. All 4 (9.1%) patients with NSS < 200 rated their BoNT-A injection result as worse than previous, and change in Voice Handicap Index-10 (VHI-10) scores were worse or without change.

CONCLUSIONS

Aiming for an NSS value greater than 200 during phonation prior to BoNT-A toxin injection for AdSD may reduce unfavorable voice outcomes.

Comprehensive Evaluation of Voice-Specific Outcomes in Patients With Essential Tremor Before and After Deep Brain Stimulation

OBJECTIVE

Deep brain stimulation (DBS) is a treatment for medically refractory essential tremor (ET), but there is a paucity of literature examining the effects of DBS on voice in patients with ET pre-DBS and post-DBS. This study aimed to report a comprehensive evaluation of voice in patients with ET pre-DBS and 6-months post-DBS.

STUDY DESIGN

Case series.

METHODS

Five patients receiving DBS for ET underwent voice evaluations pre-DBS and 6-months post-DBS. One patient had concurrent ET of the vocal tract (ETVT). The evaluation included patient-reported, perceptual, acoustic, and phonatory aerodynamic analyses of voice. Voice Handicap Index-10, Grade, Roughness, Breathiness, Asthenia, Strain Scale, perturbation measures, cepstral spectral index of dysphonia, cepstral peak prominence, and mean phonatory airflow measures were also among the data collected.

RESULTS

Patients with ET presented with minimal changes in perceptual, acoustic, and phonatory aerodynamic parameters. Perceived vocal roughness significantly increased 6-months post-DBS (P = 0.047). The patient with ETVT presented with clinically significant improvement in almost all collected voice parameters 6-months post-DBS.

CONCLUSION

This is the first study to provide data encompassing auditory perceptual voice analysis, voice-specific patient-reported quality of life measures, acoustic, and phonatory aerodynamic outcomes in patients pre-DBS and 6-months post-DBS for ET. The results of our preliminary study have implications for the use of a comprehensive voice assessment to identify and measure change in voice outcomes in patients with ET and ETVT pre- and postsurgery.

Laryngeal Electromyography-Guided Hyaluronic Acid Vocal Fold Injections for Glottic Insufficiency

OBJECTIVES

To assess voice outcomes using the novel technique of in-office laryngeal electromyography-guided vocal fold injections (LEVFI) with hyaluronic acid to treat glottal insufficiency. Secondary objectives included determining the complication/completion rates and if any factors were associated with improved voice outcomes.

METHODS

Retrospective review of patients who received their first LEVFI from August 2017 to December 2018. Three- and six-month voice outcomes were assessed. Outcomes included voice handicap index-10 (VHI-10), maximum phonation time (MPT), perceptual analysis of voice (GRBAS), fundamental frequency, and stroboscopy.

RESULTS

Of the 121 eligible patients (55.4% male, age 63.7 years), 94 (77.7%) had complete 3-month data and 59 (48.8%) had complete 6-month data. VHI-10 was significantly improved from 25.7 ± 7.5 to 20.9 ± 10.9 at 3 months (P < .001) and to 19.1 ± 11.5 at 6 months (P < .001). MPT improved from 6.2 ± 5.4 seconds to 9.4 ± 7.1 seconds at 3 months (P < .001) and to 11.3 ± 8.2 seconds at 6 months (P < .001). GRBAS was improved in 74.8% of patients ([65.2, 82.8] 95% CI) at 3 months and 80.8% ([69.9, 89.1]) 95% CI) at 6 months. Stroboscopy showed a glottic gap improvement in 74.8% of patients ([65.8, 82.4] 95% CI) at 3 months and in 80.3% ([65.9, 88.5] 95% CI) at 6 months. Fundamental frequency was unchanged, as expected. Multivariate analysis reported that no factors were associated with better voice outcomes. Overall, 177/181 (97.8%) injections were completed. There were no complications.

CONCLUSION

In-office LEVFI is an effective, novel technique to treat glottic insufficiency with improved voice outcomes, high completion rate, and no significant complications.

Microstimulation in Different Parts of the Periaqueductal Gray Generates Different Types of Vocalizations in the Cat

In the cat four different types of vocalization, mews, howls, cries, and hisses were generated by microstimulation in different parts of the periaqueductal gray (PAG). While mews imply positive vocal expressions, howls, hisses, and cries represent negative vocal expressions. In the intermediate PAG, mews were generated in the lateral column, howls, and hisses in the ventrolateral column. Cries were generated in two other regions, the lateral column of the rostral PAG and the ventrolateral column of the caudal PAG. In order to define the specific motor patterns of the mews, howls, and cries, the following muscles were recorded during these vocalizations; larynx (cricothyroid, thyroarytenoid, and posterior cricoarytenoid), tongue (genioglossus), jaw (digastric), and respiration muscles (diaphragm, internal intercostal, external, and internal abdominal oblique). During these mews, howls, and cries we analyzed the frequency, intensity, activation cascades power density, turns, and amplitude analysis of the electromyograms (EMGs). It appeared that each type of vocalization consists of a specific circumscribed motor coordination. The nucleus retroambiguus (NRA) in the caudal medulla is known to serve as the final premotor interneuronal output system for vocalization. Although neurochemical microstimulation in the NRA itself also generated vocalizations, they only consisted of guttural sounds, the EMGs of which involved only small parts of the EMGs of the mews, howls, and cries generated by neurochemical stimulation in the PAG. These results demonstrate that positive and negative vocalizations are generated in different parts of the PAG. These parts have access to different groups of premotoneurons in the NRA, that, in turn, have access to different groups of motoneurons in the brainstem and spinal cord, resulting in different vocalizations. The findings would serve a valuable model for diagnostic assessment of voice disorders in humans.

Inter-rater reliability of seven neurolaryngologists in laryngeal EMG signal interpretation

Purpose

Laryngeal electromyography (LEMG) has been considered as gold standard in diagnostics of vocal fold movement impairment, but is still not commonly implemented in clinical routine. Since the signal interpretation of LEMG signals (LEMGs) is often a subjective and semi-quantitative matter, the goal of this study was to evaluate the inter-rater reliability of neurolaryngologists on LEMGs of volitional muscle activity.

Methods

For this study, 52 representative LEMGs of 371 LEMG datasets were selected from a multicenter registry for a blinded evaluation by 7 experienced members of the neurolaryngology working group of the European Laryngological Society (ELS). For the measurement of the observer agreement between two raters, Cohen’s Kappa statistic was calculated. For the interpretation of agreements of diagnoses among the seven examiners, we used the Fleiss’ Kappa statistic.

Result

When focusing on the categories “no activity”, “single fiber pattern”, and “strongly decreased recruitment pattern”, the inter-rater agreement varied from Cohen’s Kappa values between 0.48 and 0.84, indicating moderate to near-perfect agreement between the rater pairs. Calculating with Fleiss’ Kappa, a value of 0.61 showed good agreement among the seven raters. For the rating categories, the Fleiss’ Kappa value ranged from 0.52 to 0.74, which also showed a good agreement.

Conclusion

A good inter-rater agreement between the participating neurolaryngologists was achieved in the interpretation of LEMGs. More instructional courses should be offered to broadly implement LEMG as a reliable diagnostic tool in evaluating vocal fold movement disorders in clinical routine and to develop future algorithms for therapy and computer-assisted examination.

Vocal Fold Paresis

This article discusses vocal fold paresis as a separate and distinct condition from vocal fold paralysis. The signs and symptoms of paresis may be different and less obvious than those for paralysis, so this condition is often misdiagnosed or underdiagnosed. Elements necessary to heighten clinical suspicion are included to assist in educating practitioners on these subtle findings. Once paresis is suspected, associated respiratory or sensory abnormalities also should be sought, because these may change the treatment plan when recognized. Utility of laryngeal electromyography is discussed along with potential treatment options for both the motor and often-present sensory symptoms.

The impact of cricothyroid involvement on adductor recovery in unilateral vocal fold paralysis

OBJECTIVES/HYPOTHESIS

Wide variation in postinjury functional recovery is a hallmark of unilateral vocal fold paralysis (UVFP), ranging from zero to full recovery. The present study examined the impact of cricothyroid (CT) muscle involvement on recovery using quantitative laryngeal electromyography (LEMG) of the thyroarytenoid-lateral cricoarytenoid (TA-LCA) muscle complex at multiple times postinjury.

STUDY DESIGN

Prospective cohort study in a medical center.

METHODS

Eighty-one patients with UVFP (37 males and 44 females) received an initial assessment of quantitative LEMG, stroboscope, acoustic voice analysis and 36-Item Short Form Survey quality-of-life questionnaire at 3 to 6 months after UVFP onset and a follow-up assessment at 12 months after UVFP onset.

RESULTS

The initial and follow-up assessments were performed at 4.3 ± 1.9 and 12.5 ± 1.3 months after UVFP onset, respectively. The peak turn frequency of the TA-LCA muscle complex on the lesion side was improved at the follow-up (470 ± 294 Hz) compared with the initial assessment (300 ± 204 Hz) (P < .001). Patients were also divided into two groups with (n = 27) and without (n = 54) CT involvement, respectively. TA-LCA muscle complex turn frequency improved in patients without CT involvement (from 277 ± 198 to 511 ± 301 Hz; P < .001), but not in those with CT involvement (from 345 ± 211 to 386 ± 265 Hz; P = .46). Seventy-one of all patients received early intervention with intracordal hyaluronate injection, showing similar therapeutic effects in those with and without CT involvement.

CONCLUSIONS

Acute UVFP with combined TA-LCA muscle complex and CT muscle involvement has a poor prognosis, with poorer recovery of TA-LCA muscle complex recruitment. Early interventions should be considered in patients with UVFP with CT involvement.

LEVEL OF EVIDENCE

2 Laryngoscope, 130:139-145, 2020.

Isolated Paresis of Laryngeal Adduction: What Are the Laryngoscopic and Stroboscopic Findings?

OBJECTIVES/HYPOTHESIS

This study aimed to describe the videolaryngostroboscopic (VLS) findings in a cohort of patients with isolated paresis of laryngeal adduction and identify predictive variables that may be related to voice recovery.

STUDY DESIGN

Chart review and VLS analysis of dysphonic patients diagnosed with isolated paresis of laryngeal adduction by laryngeal electromyography (LEMG).

METHODS

Demographic, clinical, VLS, and LEMG findings were analyzed according to the outcome of dysphonia.

RESULTS

There were 17 patients, 12 males (70.6%), mean age of 46.6 years, with median dysphonia duration of 4 months (range, 1-60 months) included in the study. In all patients, gross movement of both vocal folds were normal. Laryngoscopy showed limited adduction of the ipsilateral ventricular fold, contralateral interarytenoid region deviation, and vocal fold atrophy in 100%, 94.1%, and 76.5% of patients, respectively. VLS findings included: impairment of glottic closure (94.1%), phase asymmetry (94.1%), and reduced mucosal wave on the affected side (76.5%). Predictors of good voice outcome were sudden onset (P = .012), duration of dysphonia on presentation shorter than 5 months (P = .005), and absence of polyphasic potentials on LEMG (P = .041).

CONCLUSIONS

Findings on VLS as described suggest isolated paresis of laryngeal adduction and should warrant indication of LEMG for definite diagnosis. Voice improvement may be related to clinical and LEMG findings.

LEVEL OF EVIDENCE

4 Laryngoscope, 129:919-925, 2019.

Comparison of inhaled versus intravenous anesthesia for laryngoscopy and laryngeal electromyography in a rat model

Background

Propofol and remifentanil intravenous combination is one popular form of total intravenous anesthesia (TIVA) in mainstream clinical practice, but it has rarely been applied to a rat model for laryngoscopy and laryngeal electromyography (LEMG). Our objective was to establish a safe and reproducible general anesthetic protocol for laryngoscopy and endoscopic LEMG in a rat model. Our hypothesis is that TIVA allows a minimally morbid, and feasible laryngoscopy and LEMG.

Methods

Sprague Dawley rats were subjected to either inhalational anesthesia (IA) (isoflurane) or TIVA (propofol and remifentanil) and underwent laryngoscopy and LEMG. The primary outcome was a complete minimally interrupted rigid laryngoscopy and obtaining reproducible motor unit potentials from the posterior cricoarytenoid muscles. The secondary outcome was morbidity and mortality.

Results

Seventeen out of twenty-two rats underwent both TIVA and IA. Only two underwent IA only. All nineteen rats that underwent IA had a successful experiment. Seventeen rats underwent TIVA, however, only nine completed a successful experiment due to difficulty achieving a surgical plane, and respiratory events. Upon comparing the success of the two anaesthetic regimens, IA was superior to TIVA (P = 0.0008). There was no statistical difference between the amplitudes (p = 0.1985) or motor units burst duration (p = 0.82605) of both methods. Three mortalities were encountered, one of which was due to lidocaine toxicity and two were during anesthetic induction. Respiratory related morbidity was encountered in two rats, all seen with TIVA.

Conclusions

TIVA is not an ideal anesthetic regimen for laryngeal endoscopy and LEMG in rat models. Contrary to our hypothesis, IA did not affect the quality of the LEMG and allowed a seamless rigid endoscopy.

Electronic supplementary material

The online version of this article (10.1186/s40463-018-0312-9) contains supplementary material, which is available to authorized users.

Vocal fold paresis: Medical specialists' opinions on standard diagnostics and laryngeal findings

PURPOSE

There is still no clear consensus on the diagnostic value of specific laryngeal findings in patients with suspected vocal fold paresis (VFP). The aim of the study was to establish expert opinion on criteria for the diagnosis of VFP in Europe.

METHODS

A cross-sectional survey using the questionnaire introduced by Wu and Sulica for US American experts was addressed to laryngeal experts in Germany, Austria, and Switzerland and in a second survey wave to members of the European Laryngological Society.

RESULTS

100 respondents returned survey 1 (response rate 47.2%). 26% worked at a university department. 28% regularly used laryngeal electromyography (LEMG). A pathologic test results in LEMG was considered to have the strongest positive predictive value for VFP (79 ± 23%), followed by a decreased vocal fold abduction (70 ± 29%), decreased vocal fold adduction (61 ± 34%), and atrophy of the hemilarynx (61 ± 31%). The multivariate analysis showed the predictive value of LEMG was estimated lower by respondents from non-university hospital (β = - 16.33; confidence interval (CI) = - 25.63 to - 7.02; p = 0.001) and higher in hospitals with higher frequency of VFP patients per months (β = 1.57; CI = - 0.98 to 2.16; p < 0.0001). 30 ELS members returned survey 2 (response rate, 8.4%). Their answers were not significantly different to survey 1.

CONCLUSIONS

The laryngology experts in Europe rely on LEMG for diagnosis of VFP like the US American experts, but paradoxically only a minority uses LEMG frequently. Next to LEMG, motion abnormities were considered to have the best predictive value for the diagnosis of VFP.

Impact of recurrent laryngeal nerve lesion on oropharyngeal muscle activity and sensorimotor integration in an infant pig model

The successful performance of a swallow requires dynamic integration between a wide range of sensory inputs and muscle activities to produce the coordinated kinematics of oropharyngeal structures. Damage to the recurrent laryngeal nerve (RLN) produces dysphagia in infants, with food or liquid entering the airway despite this nerve having minimal direct sensory or motor connections to the act of swallowing, apart from vocal fold closure. Previous results have demonstrated that a complete RLN lesion disrupts both performance and kinematics before initiation of the pharyngeal swallow in infants. We tested the hypothesis that a RLN lesion produces changes in the normal activity of oral floor, tongue, and infrahyoid muscles during a swallow. We recorded swallowing in our validated infant pig model, with synchronous high-speed imaging and fine-wire, chronic electromyography. We found changes in the timing, duration, and amplitude of the motor pattern in an array of muscles that are supplied by several different cranial and cervical nerves. Some of these changes in muscle activity are associated with the preparatory aspects of bolus aggregation or movement and so occur before the pharyngeal swallow. Taken with previous biomechanical results, these patterns suggest an intricate brain stem sensorimotor integration that occurs as part of a swallow. In particular, the execution of oral motor function is changed as a result of this simple lesion. NEW & NOTEWORTHY Damage to the recurrent laryngeal nerve compromises swallowing despite an absent or minimal contribution to either the motor or sensory aspects of this function. This study documents EMG changes, following RLN lesion, to non-RLN innervated muscles that are active during swallowing in an infant model. Some of these muscles fire before the pharyngeal swallow and are associated with the preparatory aspects of bolus aggregation and movement, suggesting important sensorimotor integration at a brain stem level.

Spasmodic Dysphonia: A Review. Part 2: Characterization of Pathophysiology

Objective

The purpose of this review is to describe the recent advances in characterizing spasmodic dysphonia. Spasmodic dysphonia is a task-specific focal laryngeal dystonia characterized by irregular and uncontrolled voice breaks. The pathophysiology is poorly understood, and there are diagnostic difficulties.

Data Sources

PubMed, Google Scholar, and Cochrane Library.

Review Methods

The data sources were searched using the following search terms: ( spasmodic dysphonia or laryngeal dystonia) and ( etiology, aetiology, diagnosis, pathogenesis, or pathophysiology).

Conclusion

The diagnosis of spasmodic dysphonia can be difficult due to the lack of a scientific consensus on diagnostic criteria and the fact that other voice disorders may present similarly. Confusion can arise between spasmodic dysphonia and muscle tension dysphonia. Spasmodic dysphonia symptoms are tied to particular speech sounds, whereas muscle tension dysphonia is not. With the advent of more widespread use of high-speed laryngoscopy and videokymography, measures of the disruptions in phonation and delays in the onset of vocal fold vibration after vocal fold closure can be quantified. Recent technological developments have expanded our understanding of the pathophysiology of spasmodic dysphonia.

Implications for Practice

A 3-tiered approach, involving a questionnaire, followed by speech assessment and nasolaryngoscopy is the most widely accepted method for making the diagnosis in most cases. More experimental and invasive techniques such as electromyography and neuroimaging have been explored to further characterize spasmodic dysphonia and aid in diagnosing difficult cases.

Continuous intraoperative neural monitoring in thyroid surgery: a Mexican experience

Intraoperative continuous neural monitoring (C-IONM) during thyroid surgery has been recognized as a useful tool to identify and confirm recurrent laryngeal nerve integrity. The aim of the present study is to analyze electromyographic features and thresholds for normal vocal fold function in our initial experience with C-IONM in thyroid surgery. C-IONM was utilized in 57 patients who underwent thyroid surgery between July 2012 and December 2015. EMG parameters were analyzed looking for potential predictors of postoperative vocal fold dismotility. There were 54 females (94.7%) and 3 males (5.3%) with a mean age of 46.7 ± 11.6 years. C-IONM was successfully registered in 89 of 107 nerves at risk (83.1%). Mean basal amplitude was 727.31 ± 471.25 μV and mean final amplitude was 650.27 ± 526.87 μV (P = 0.095, CI 95% 13.83-167.91). Mean basal latency was 5.23 ± 1.42 mS and mean final latency was 5.18 ± 1.50 mS (P = 0.594, CI 95% 0.39-0.24). Four patients had transient postoperative vocal fold paresis. None of these four patients had loss of signal (LOS), three had transient decrease in amplitude, and one had a normal registry throughout the operation. C-IONM is a useful tool to identify patients in whom intraoperative RLN is at risk during surgery. Final amplitude above 500 μV and no LOS is associated with RLN integrity and normal postoperative vocal fold function.

Laryngeal electromyographic changes in postthyroidectomy patients with normal vocal cord mobility

Thyroidectomy has been used for the treatment of thyroid disease for more than 100 years. In spite of the advancement of surgical techniques, there is still a risk of laryngeal nerve injury. The risk of partial or complete injury still depends on some surgical and disease-related factors. The aim of this study is to show the partial injury and to establish these risk factors via laryngeal electromyographic analysis (LEMG) in postthyroidectomy patients with normal vocal cord motion and mucosal anatomy. Patients who had undergone thyroid surgery were enrolled in this prospective study. LEMG analysis was performed to all patients with normal vocal cord mobility preoperatively and was repeated after the first and the third months of surgery. Thyroarytenoid (TA) and cricothyroid (CT) muscles were used to evaluate recurrent and external branch of superior laryngeal nerves, respectively. Four of the 32 patients had mild-to-moderate degrees of partial LEMG changes during preoperative LEMG analysis of TA and CT muscles on each side. After 3 months of surgery, there was a statistically significant worsening of LEMG findings in the right and left external branches of superior and left recurrent laryngeal nerves. Disease and surgery-related risk factors were analyzed. However, there was no significant relationship on the progression of LEMG findings according to these parameters. This is the first prospective study which supports the risk of progression of LEMG changes in patients with normal laryngoscopic examination after thyroid surgery. No reliable significant risk factor was found influencing the LEMG progression.

Animal Models for Dysphagia Studies: What Have We Learnt So Far

Research using animal models has contributed significantly to realizing the goal of understanding dysfunction and improving the care of patients who suffer from dysphagia. But why should other researchers and the clinicians who see patients day in and day out care about this work? Results from studies of animal models have the potential to change and grow how we think about dysphagia research and practice in general, well beyond applying specific results to human studies. Animal research provides two key contributions to our understanding of dysphagia. The first is a more complete characterization of the physiology of both normal and pathological swallow than is possible in human subjects. The second is suggesting of specific, physiological, targets for development and testing of treatment interventions to improve dysphagia outcomes.

Effect of Levodopa + Carbidopa on the Laryngeal Electromyographic Pattern in Parkinson Disease

BACKGROUND

Vocal impairment is one of the main debilitating symptoms of Parkinson disease (PD). The effect of levodopa on vocal function remains unclear.

OBJECTIVE

This study aimed to determine the effect of levodopa on electromyographic patterns of the laryngeal muscle in patients with PD.

STUDY DESIGN

This is a prospective interventional trial.

METHODS

Nineteen patients with PD-diagnosed by laryngeal electromyography-were enrolled. Cricothyroid and thyroarytenoid (TA) muscle activities were measured at rest and during muscle contraction (phonation), when participants were on and off medication (12 hours after the last levodopa dose).

RESULTS

Prevalence of resting hypertonia in the cricothyroid muscle was similar in the off and on states (7 of 19, P = 1.00). Eight patients off medication and four patients on medication had hypertonic TA muscle at rest (P = 0.289). No electromyographic alterations were observed during phonation for either medication states.

CONCLUSION

Despite a tendency for increased rest tracings in the TA muscle when participants were on medication, no association was found between laryngeal electromyography findings and levodopa + carbidopa administration.

Diagnostic and prognostic contribution of laryngeal electromyography in unilateral vocal-fold immobility in adults

OBJECTIVES

To study the diagnostic and prognostic contribution of laryngeal electromyography in unilateral vocal-fold immobility in adults.

MATERIAL AND METHODS

A retrospective study included patients with unilateral vocal-fold immobility undergoing laryngeal electromyography between 2007 and 2015. Neurogenic, normal or myogenic findings were compared to the clinical aspect. Prognosis for recovery was assessed from motor unit potentials on laryngeal electromyography, and compared to subsequent progress on laryngoscopy.

RESULTS

Sixty-three patients (mean age, 59 years) were initially included; 2 were subsequently excluded from analysis. Mean time from onset of immobility to laryngeal electromyography was 7 months. 85% of the 61 patients showed neurogenic findings, indicating neural lesion; 13% showed normal electromyography, indicating cricoarytenoid joint ankylosis; and 1 patient showed a myogenic pattern. Neurogenic cases were usually secondary to cervical surgery. Thirty-eight patients were followed up. In total, 75% of patients showing reinnervation potentials recovered. The positive predictive value of laryngeal electromyography was 69.2%.

CONCLUSION

Laryngeal electromyography is effective in specifying the origin of unilateral vocal-fold immobility in adults. It also has a prognostic role, lack of reinnervation potentials being a possible indication for early medialization surgery.

Botulinum toxin injection in laryngeal dyspnea

Data, regarding the use of botulinum toxin (BT-A) in laryngeal dyspnea, are scarce, coming from some cases reports in the literature, including Vocal fold paralysis, laryngeal dystonia, vocal cord dysfunction also called paradoxical motion of the vocal fold (PMVF), and post-neuroleptic laryngeal dyskinesia. There is no consensus regarding the muscles and the doses to inject. The aim of this study is to present a retrospective review of patients treated in our ENT Department by BT-A injection in this indication. This study is a retrospective study describing patients who underwent an injection of botulinum toxin for laryngeal dyspnea in the ENT Department from 2005 to 2015 years. The inclusion criteria were a dyspnea associated with a laryngeal dysfunction, confirmed by flexible fiberoptic nasopharyngolaryngoscopy. Information concerning the causes of the dyspnea, the botulinum toxin BT-A injections procedure, post-injection follow-up, and respiratory outcome were collected for all patients included. In the group of 13 patients included, the main cause identified as principal factor linked with the short breath was: a bilateral VF paralysis (Patel et al., Otolaryngol Head Neck Surg 130:686-689, 7), laryngeal dystonia (Balkissoon and Kenn, Semin Respir Crit Care Med 33:595-605, 2), Anxiety syndrome associated with unilateral vocal fold paralysis or asthma (Marcinow et al., Laryngoscope 124:1425-1430, 3), and an isolated asthma (Zwirner et al., Eur Arch Otorhinolaryngol 254:242-245, 1). Nine out of the thirteen patients were improved by the injections. A BT-A-induced stable benefit for four patients led them to stop the injections in the follow-up. Good outcome was observed in five other patients (main cause: bilateral VP paralysis), allowing a progressive lengthening of the delay between BT-A injections. Four patients did not report a positive risk/benefit ratio after BT-A injections; two of them (with bilateral VF paralysis), because of respiratory side effects and lack of benefit without the side effects for the two others. This failure of effect was not related with BT-A doses injected. This study provides support for using BT-A injections as a symptomatic treatment of periodic laryngeal dyspnea, regardless of the etiologic context. From our data, we suggest that a small starting dose (of around 4 U BT-A Botox^®) could be enough for a first injection to obtain a good benefit. The target muscle should be determined by the EMG analysis.

Diagnosis and management of unilateral thyroarytenoid muscle palsy

The objective of this study is to assess and propose a method of diagnosis and management of patients with unilateral thyroarytenoid muscle palsy (TAMP). This is a retrospective review of clinical records. The records of seven patients diagnosed as having idiopathic TAMP were reviewed. Despite the adductive and abductive functions of the vocal folds being within normal range, apparent palsy was seen in the unilateral thyroarytenoid muscle of these patients. TAMP was confirmed by laryngeal electromyography, and the adductive and abductive movements of the vocal folds were evaluated as the mobility of the arytenoid cartilages by three-dimensional computed tomography and endoscopy. Most of patients with TAMP had been diagnosed as having other diseases or normal, and in one patient, it took over 6 years to establish a correct diagnosis. Two patients recovered by conservative treatment; however, in five patients, TAMP remained even after 6 months. In 4 of those 5 patients, treatment with hyaluronic acid injections was performed. In the remaining patient, surgical treatment, namely, nerve-muscle pedicle flap implantation was performed, which resulted in a favorable recovery of phonation. The average maximum phonation time (MPT) of all patients was extended from 11.4 (±4.4) s before treatment to 19.9 (±4.3) s after treatment, and the pitch range was also increased from 25.1 (±7.2) to 34.6 (±5.8) semitones following our management course. Our results indicate that there is a possibility that TAMP can be diagnosed and treated sufficiently. Therefore, further research toward establishing the concept of and treatment for TAMP is anticipated.

Laryngeal Reflexes: Physiology, Technique, and Clinical Use

This review examines the current level of knowledge and techniques available for the study of laryngeal reflexes. Overall, the larynx is under constant control of several systems (including respiration, swallowing and cough) as well as sensory motor reflex responses involving glossopharyngeal, pharyngeal, laryngeal, and tracheobronchial sensory receptors. Techniques for the clinical assessment of these reflexes are emerging and need to be examined for sensitivity and specificity in identifying laryngeal sensory disorders. Quantitative assessment methods for the diagnosis of sensory reductions and sensory hypersensitivity may account for laryngeal disorders, such as chronic cough, paradoxical vocal fold disorder, and muscular tension dysphonia. The development of accurate assessment techniques could improve our understanding of the mechanisms involved in these disorders.

Posterior cricoarytenoid muscle electrophysiologic changes are predictive of vocal cord paralysis with recurrent laryngeal nerve compressive injury in a canine model

OBJECTIVES/HYPOTHESIS

Injury to the recurrent laryngeal nerve (RLN) is a dreaded complication of endocrine surgery. Intraoperative neural monitoring (IONM) has been increasingly utilized to assess the functional status of the RLN. Although the posterior cricoarytenoid muscle (PCA) is innervated by the RLN as the abductor of the larynx, PCA electromyography (EMG) is infrequently recorded during IONM and PCA activity after RLN compressive injury remains poorly characterized.

STUDY DESIGN

Single-subject prospective animal study.

METHODS

We employed a canine model to identify postcricoid EMG correlates of postoperative vocal cord paralysis (VCP). Postcricoid electrode recordings were obtained before and after compressive RLN injury associated with VCP.

RESULTS

Normative postcricoid recordings revealed mean amplitude of 1288 microvolt (μV) and latency of 8.2 millisecond (ms) with maximum (1 milliamp [mA]) vagal stimulation, and mean amplitude of 1807 μV and latency of 3.5 ms with maximum (1 mA) RLN stimulation. Following injury that was associated with VCP, there was 62.1% decrement in postcricoid EMG amplitude with maximum vagal stimulation and 80% decrement with maximum RLN stimulation. Threshold stimulation of the vagus increased by 23%, and there was a corresponding 42% decrease in amplitude. For RLN stimulation, latency increased by 17.3% following injury, whereas threshold stimulation increased by 61% with 35.5% decrement in EMG amplitude. Thus, if RLN amplitude decreases by ≥ 80%, with absolute amplitude of ≤ 300 μV or less and latency increase of ≥ 10%, RLN injury is likely associated with VCP.

CONCLUSION

Our results predict postoperative VCP based on postcricoid electromyographic IONM and may guide surgical decision making.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:2744-2751, 2016.

Prognostic Relevance of Mucosal Waves in Patients With Unilateral Vocal Fold Paralysis

OBJECTIVES

To analyze the prognostic relevance of mucosal waves (MWs) for recovery of unilateral vocal fold paralysis (UVP).

METHODS

The charts and stroboscopic examinations of 100 consecutive patients with a complete UVP were reviewed retrospectively. All had a minimal (estimated <3 mm) mucosal gap on stroboscopy. A positive or negative MW on the paralyzed vocal fold was associated with complete recovery to full adduction and abduction. All patients were followed for at least 12 months.

RESULTS

Causes of the paralysis were iatrogenic/traumatic (n = 82), malignancy associated (n = 10), and idiopathic (n = 8). In patients with positive MW at diagnosis (n = 80), the chance of recovery of unilateral vocal fold paralysis was 91.25%, whereas the chance of recovery with a negative mucosal wave (n = 20) was only 10%.

CONCLUSION

Positive MWs in stroboscopy are a predictor for recovery of (iatrogenic/traumatic) unilateral vocal fold paralysis and should be used in routine diagnostic assessment.

Motor organization of positive and negative emotional vocalization in the cat midbrain periaqueductal gray

Neurochemical microstimulation in different parts of the midbrain periaqueductal gray (PAG) in the cat generates four different types of vocalization, mews, howls, cries, and hisses. Mews signify positive vocal expression, whereas howls, hisses, and cries signify negative vocal communications. Mews were generated in the lateral column of the intermediate PAG and howls and hisses in the ventrolateral column of the intermediate PAG. Cries were generated in two regions, the lateral column of the rostral PAG and the ventrolateral column of the caudal PAG. To define the specific motor patterns belonging to mews, howls, and cries, the following muscles were recorded during these vocalizations: larynx (cricothyroid, thyroarytenoid, and posterior cricoarytenoid), tongue (genioglossus), jaw (digastric), and respiration (diaphragm, internal intercostal, external abdominal oblique, and internal abdominal oblique) muscles. Furthermore, the frequency, intensity, activation cascades, and turns and amplitude analyses of the electromyograms (EMGs) during these vocalizations were analyzed. The results show that each type of vocalization consists of a specific, circumscribed motor coordination. The nucleus retroambiguus (NRA) in the caudal medulla serves as the final premotor interneuronal output system for vocalization. NRA neurochemical microstimulation also generated vocalizations (guttural sounds). Analysis of the EMGs demonstrated that these vocalizations consist of only small parts of the emotional voalizations generated by neurochemical stimulation in the PAG. These results demonstrate that motor organization of positive and negative emotional vocal expressions are segregated in the PAG and that the PAG uses the NRA as a tool to gain access to the motoneurons generating vocalization.

Vocal cord paralysis predicted by neural monitoring electrophysiologic changes with recurrent laryngeal nerve compressive neuropraxic injury in a canine model

BACKGROUND

Recurrent laryngeal nerve (RLN) injury is a known complication of thyroid/parathyroid surgery. Intraoperative nerve monitoring (IONM) has been used to gain more information regarding the functional status of the RLN intraoperatively; however, the electromyography (EMG) parameters of RLN after nontransection neuropraxic compressive injury remain unknown.

METHODS

We developed a canine model to identify IONM EMG correlates of postoperative vocal cord paralysis (VCP) using a standardized method to simulate surgical RLN compression sufficient to cause VCP.

RESULTS

Compression nerve injury decreased EMG amplitude and increased EMG latency, with a 60% increase in RLN threshold stimulation compared to preinjury values. If RLN amplitude decreases by 80% with an absolute amplitude of 300 μV or less in combination with a latency increase of 10% or more, then nerve injury and associated VCP is likely.

CONCLUSION

These results may help surgeons to prognosticate postoperative neural function and intraoperative decision-making regarding contralateral thyroid surgery. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1341-E1350, 2016.

Multi-Motor Unit Potential Analysis and Other Quantitative Techniques for Laryngeal Electromyogram

Reference values for motor unit potentials of laryngeal muscles, the thyroarytenoid (TA) and cricothyroid (CT) muscles, have been collected using multi-motor unit potential quantitative electromyogram analysis technique with concentric quantitative electromyogram-needle electrode type in 40 healthy volunteers. The method is well tolerated, easy to perform, and examination of one muscle takes usually around 5 minutes. The mean motor unit potential amplitude of both muscles was significantly larger in men than in women. The method can safely be used in clinical routine. Other quantitative electromyogram methods are also shortly reviewed.

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.