Interarytenoid Muscle Research Articles

Glottal Voice Distortions: Nasolaryngoscopic and Spectral Analysis of Anatomophysiologic Changes in Singing Voice.

The distorted voices, commonly called vocal drives in Brazil and in some other South American countries, are vocal ornaments belonging to the aesthetics of popular singing and desired by singers of different styles. The advances in vocal sciences have allowed the demystification of this type of technique in the last four decades, classifying them as glottal, supraglottic or mixed distortions/drives. The interdisciplinary approach in the evaluation of singers who use glottal distortions is fundamental for a broad understanding of the particularities of each case. The present study has as main objective to describe the anatomophysiological and spectral findings of the glottal distortions, identified in the practice of many singers. A sample of three singers in a sung emission with and without vocal distortions was collected. PreSonus® AudioBox Studio One kit was used to record the voice during the nasolaryngoscopic evaluation. The singers underwent vocal warm-up and functional evaluation of the larynx based on two studies on contemporary singers. The singers performed the Snarl Voice and Phaser distortions and both showed particular anatomophysiological behaviors. The larynx was low in the first distortion and the level of the clean voice in the second, with the posterior opening of the glottis in both distortions being observed, with opening of the middle third of the glottis for the first as well. Formants vary according to the vocal tract settings used for the distortions. The glottic distortions present a complex anatomophysiological behavior in their composition, with fundamental participation of the transverse interarytenoid muscle and lateral cricoarytenoids, as well as the the participation of the vocal fold in the frequency break. F3 varied according to the longitudinal length and F4 with the diameter, both being related to the three-dimensional adjustments of the vocal tract.

An Euler–Bernoulli-type beam model of the vocal folds for describing curved and incomplete glottal closure patterns

Incomplete glottal closure is a laryngeal configuration wherein the glottis is not fully obstructed prior to phonation. It has been linked to inefficient voice production and voice disorders. Various incomplete glottal closure patterns can arise and the mechanisms driving them are not well understood. In this work, we introduce an Euler–Bernoulli composite beam vocal fold (VF) model that produces qualitatively similar incomplete glottal closure patterns as those observed in experimental and high-fidelity numerical studies, thus offering insights into the potential underlying physical mechanisms. Refined physiological insights are pursued by incorporating the beam model into a VF posturing model that embeds the five intrinsic laryngeal muscles. Analysis of the combined model shows that co-activating the lateral cricoarytenoid (LCA) and interarytenoid (IA) muscles without activating the thyroarytenoid (TA) muscle results in a bowed (convex) VF geometry with closure at the posterior margin only; this is primarily attributed to the reactive moments at the anterior VF margin. This bowed pattern can also arise during VF compression (due to extrinsic laryngeal muscle activation for example), wherein the internal moment induced passively by the TA muscle tissue is the predominant mechanism. On the other hand, activating the TA muscle without incorporating other adductory muscles results in anterior and mid-membranous glottal closure, a concave VF geometry, and a posterior glottal opening driven by internal moments induced by TA muscle activation. In the case of initial full glottal closure, the posterior cricoarytenoid (PCA) muscle activation cancels the adductory effects of the LCA and IA muscles, resulting in a concave VF geometry and posterior glottal opening. Furthermore, certain maneuvers involving co-activation of all adductory muscles result in an hourglass glottal shape due to a reactive moment at the anterior VF margin and moderate internal moment induced by TA muscle activation. These findings have implications regarding potential laryngeal maneuvers in patients with voice disorders involving imbalances or excessive tension in the laryngeal muscles such as muscle tension dysphonia.

The Internal Superior Laryngeal Nerve in Humans: Evidence for Pure Sensory Function.

To determine if the internal branch of the superior laryngeal nerve (iSLN) provides direct motor innervation to the interarytenoid muscle, a laryngeal adductor critical for airway protection. We studied the iSLN-evoked motor response in the interarytenoid and other laryngeal muscles. If the iSLN is purely sensory, there will be no detectable short latency motor response upon supramaximal stimulation, indicating the absence of a direct efferent conduction path. Intraoperative case series. In seven anesthetized patients undergoing laryngectomy for unilateral laryngeal carcinoma, the iSLN of the unaffected side was electrically stimulated intraoperatively with 0.1-ms pulses of progressive intensities until supramaximal stimulation was reached. Electromyographic responses were measured in the ipsilateral interarytenoid, thyroarytenoid, and cricothyroid muscles. None of the subjects exhibited short-latency interarytenoid motor responses to iSLN stimulation. Supramaximal electrical stimulation of the intact iSLN evoked ipsilateral motor responses with long latencies: 18.7-38.5 ms in the interarytenoid (n = 6) and 17.8-24.9 ms in the thyroarytenoid (n = 5). Supramaximal stimulation of the recurrent laryngeal nerve evoked ipsilateral motor responses with short latencies: 1.6-3.9 ms in the interarytenoid (n = 6) and 1.6-2.7 ms in the thyroarytenoid (n = 6). The iSLN provides no functional efferent motor innervation to the interarytenoid muscles. The iSLN exclusively evokes an interarytenoid motor response via afferent activation of central neural circuits that mediate the laryngeal reflex arc. These findings suggest that the role of the iSLN in vital laryngopharyngeal functions, such as normal swallowing and protection of the airway from aspiration, is purely sensory. 4 Laryngoscope, 131:E207-E211, 2021.

Are the interarytenoid muscles supplied by branches of both the recurrent and superior laryngeal nerves?

It has been generally accepted that the branches of the internal branch of the superior laryngeal nerve to the interarytenoid muscle are exclusively sensory. However, some experimental studies have suggested that these branches may contain motor axons, and therefore that the interarytenoid muscle is supplied by both the superior and recurrent laryngeal nerves. The aim of this work was to determine whether motor axons to the interarytenoid muscles are present in both laryngeal nerves. Basic research. Twelve human internal branches of the superior laryngeal nerve were dissected, and its branches to the interarytenoid muscle were removed and processed for choline-acetyltransferase immunohistochemistry, a method not used previously in studying the nerve fiber composition of the laryngeal nerves. The internal branch of the superior laryngeal nerve divided into two to five branches to the interarytenoid muscle. All branches contained motor axons, with the proportion of motor axons varying from 6% to 31%. The present study confirms that the internal branch of the superior laryngeal nerve provides a motor innervation to the interarytenoid muscles. N/A. Laryngoscope, 126:1117-1122, 2016.

Failed organ preservation strategy for adult laryngeal embryonal rhabdomyosarcoma

PurposeTo present a case of embryonal rhabdomyosarcoma of the intrinsic laryngeal musculature and discuss the treatment of this rare tumor. Methods and materialsA 45year-old male presented with an eleven month history of hoarseness. A mass of the posterior glottis was noted on fiberoptic laryngoscopy. Computed tomography indicated a 1.5×2.5cm laryngeal mass without cartilage involvement. Direct laryngoscopy and biopsy were consistent with embryonal rhabdomyosarcoma involving the interarytenoid muscle. A multidisciplinary tumor board recommended multimodality therapy including total laryngectomy. His case was reviewed along with the available English language literature. ResultsThe patient refused surgery, and he qualified for a pediatric rhabdomyosarcoma treatment protocol with induction chemotherapy followed by combined chemoradiation. There was no noted response and the patient was taken off protocol to increase the radiation dose without chemotherapy. Fifteen weeks following radiation, a repeat biopsy revealed viable tumor. The patient elected further experimental chemotherapy at an outside hospital. The patient currently is alive at 34months post-treatment with suspected persistent disease and continues to refuse surgery. ConclusionsEmbryonal rhabdomyosarcoma involving the larynx is an extremely rare tumor usually seen in children. There have been few previous adult cases reported and treatment options are not well described. We present a case of chemoradiation failure in an adult with embryonal rhabdomyosarcoma refusing surgical intervention. Although pediatric tumors can be effectively treated with organ preservation strategies, adult tumors may have a poorer response. Based upon our experience and existing literature regarding adult embryonal rhabdomyosarcoma of the larynx, multimodality therapy including surgical resection should be the treatment of choice.

Nerve branches to the posterior cricoarytenoid muscle may complicate the laryngeal reinnervation procedure

To better understand the reason for the low success rate of posterior cricoarytenoid (PCA) muscle reinnervation, we attempted to identify the communicating branches that may exist between the nerve branch to the PCA muscle and the other laryngeal adductors in addition to the interarytenoid (IA) muscle. Quantitative histological assessment. Twenty human hemilarynges from patients with laryngeal or hypopharyngeal cancer were obtained after surgery and stained with Sihler's stain, which rendered the muscle translucent while counterstaining the neuroanatomy of the recurrent laryngeal nerve (RLN) inside the larynges. The nerve supply to the PCA muscle was separated into two main branches. One upper branch supplied the horizontal compartment, and the lower branch supplied the vertical/oblique compartment. In 14 specimens, two nerve branches to the PCA muscle arose separately from the RLN. In six specimens, one single main branch arose from the RLN and immediately ramified into two secondary branches. In all specimens except one, the nerve branch to the horizontal compartment was connected to the IA muscle. However, no communicating branches were observed between the nerve to the PCA muscle and the other laryngeal adductors. No anastomosis between nerve branches to the horizontal and vertical/oblique compartments or other variations of nerve distribution were observed. The communicating branches between the nerve branches to the PCA muscle and the IA muscle may be the only branch, complicating the reinnervation procedure. More investigations are needed to identify variations in the terminal branch distribution from the RLN. NA.

Influence and interactions of laryngeal adductors and cricothyroid muscles on fundamental frequency and glottal posture control.

The interactions of the intrinsic laryngeal muscles (ILMs) in controlling fundamental frequency (F0) and glottal posture remain unclear. In an in vivo canine model, three sets of intrinsic laryngeal muscles-the thyroarytenoid (TA), cricothyroid (CT), and lateral cricoarytenoid plus interarytenoid (LCA/IA) muscle complex-were independently and accurately stimulated in a graded manner using distal laryngeal nerve stimulation. Graded neuromuscular stimulation was used to independently activate these paired intrinsic laryngeal muscles over a range from threshold to maximal activation, to produce 320 distinct laryngeal phonatory postures. At phonation onset these activation conditions were evaluated in terms of their vocal fold strain, glottal width at the vocal processes, fundamental frequency (F0), subglottic pressure, and airflow. F0 ranged from 69 to 772 Hz and clustered into chest-like and falsetto-like groups. CT activation was always required to raise F0, but could also lower F0 at low TA and LCA/IA activation levels. Increasing TA activation first increased then decreased F0 in all CT and LCA/IA activation conditions. Increasing TA activation also facilitated production of high F0 at a lower onset pressure. Independent control of membranous (TA) and cartilaginous (LCA/IA) glottal closure enabled multiple pathways for F0 control via changes in glottal posture.

The role of the posterior cricoarytenoid muscle in phonation

The posterior cricoarytenoid muscle (PCA) is generally considered to be a respiratory muscle. Indeed, as the sole abductor of the glottis (i.e., the only laryngeal muscle with the capability of opening the true vocal folds), paralysis of the PCA may lead to asphyxiation. While the PCA muscle also appears to play a role in phonation, a consensus has not been reached among voice scientists regarding its precise role in the control of fundamental frequency, phonation threshold pressure, and other phonatory variables. Using a new developed method of graded stimulation to the laryngeal muscles, Chhetri, Neubauer, and Berry (2012) explored the role of the cricothyroid muscle (CT), thyroarytenoid muscle (TA), and the lateral cricoarytenoid and interarytenoid muscle complex (LCA + IA) on fundamental frequency, phonation threshold pressure and glottal posturing. The present study augments the previous study by also investigating the influence of the PCA muscle on these same phonatory variables. Similar to the adductor muscles, it is shown that the PCA muscle introduces new possibilities for achieving multiple phonation types at a given fundamental frequency.

Interarytenoid botulinum toxin injection for recalcitrant vocal process granuloma

This study evaluated the efficacy of botulinum toxin type A injected into the interarytenoid muscle to treat recalcitrant vocal process granulomas. Retrospective clinical review at a tertiary care center. Eight patients with vocal process granulomas refractory to a variety of prior treatments including surgical resection, proton pump inhibitor therapy, and voice therapy underwent percutaneous injection of botulinum toxin type A into the interarytenoid muscle, performed in an office setting. Doses ranged from 5 U to 25 U in one to two injections. One patient demonstrated no improvement, two patients demonstrated partial resolution, and five patients demonstrated complete resolution of their granulomas. Four patients noted transient breathiness. There were no other side effects. All patients tolerated the injections without difficulty. Botulinum toxin injection into the interarytenoid muscle appears to be a safe and effective modality for treating recalcitrant vocal process granuloma.

Partial cricotracheal resection with tracheal intussusception and cricoarytenoid joint mobilization: Early experience in a new technical variant

Partial cricotracheal resection with tracheal intussusception and cricoarytenoid joint mobilization: Early experience in a new technical variant

Interarytenoid Muscle Botox Injection for Treatment of Adductor Spasmodic Dysphonia With Vocal Tremor

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

Establishing a New Animal Model for the Study of Laryngeal Biology and Disease: An Anatomic Study of the Mouse Larynx

Animal models have contributed greatly to the study of voice, permitting the examination of laryngeal biology and the testing of surgical, medical, and behavioral interventions. Various models have been used. However, until recently, the mouse (Mus musculus) has not been used in laryngeal research, and features of the mouse larynx have not been defined. Therefore, the purpose of this study was to qualitatively describe mouse laryngeal anatomy in relation to known human anatomy. Larynges of 7 C57BL mice were examined and photographed under stereotactic and light microscopy. The authors found that mouse laryngeal organization was similar to that of humans. The hyoid bone and epiglottal, thyroid, cricoid, and arytenoid cartilages were identified. An additional cartilage was present ventrally. Thyroarytenoid, posterior cricoarytenoid, lateral cricoarytenoid, and cricothyroid muscles were grossly positioned as in humans. Interarytenoid muscles were not present; however, a functional counterpart was identified. The authors provide an initial description of mouse laryngeal anatomy. Because of its amenability to genetic engineering, the mouse is the premiere model for the study of disease and the testing of interventions. Introduction of the mouse model for laryngeal study offers a tool for the study of normal laryngeal cell biology and tissue response to disease processes.

Anatomic study of human laryngeal ganglia: Number and distribution

We have studied 12 laryngeal nerves: six internal branches of the superior laryngeal nerve (ILN) and six recurrent laryngeal nerves (RLN) from three human adult larynges (two males and one female). After dissection of each individual laryngeal nerve using a surgical microscope, the nerves were preserved in 10% formalin, embedded in paraffin wax, serially sectioned transversely at a thickness of 10 microm and stained with hematoxylin and eosin. We found 2-4 ganglia associated with the ILN. At least two ganglia were always present (six out of six cases), the largest one being associated with the branch of the nerve innervating the vestibule and the smallest one associated with the branch innervating the aryepiglottic fold. Other ganglia were found associated with the branches for the glosso-epiglottic fold and vallecula (four out of six cases) and interarytenoid muscle (three out of six cases). The RLN showed from two to six ganglia, all of them located in its anterior terminal division. Two of the ganglia were located in the part of the nerve between the origin of the branches for the interarytenoid and lateral cricoarytenoid muscles (three out of six cases). The remaining ganglia were located close to or at the origin of the muscular branches innervating the intrinsic laryngeal muscles. The cytology of the ganglia reported suggests that they were all autonomic in nature, probably parasympathetic.

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.

The Innervation of the Posterior Cricoarytenoid Muscle: Exploring Clinical Possibilities

Manipulation of the nerve supply to the posterior cricoarytenoid (PCA) muscle has potential for ameliorating the symptoms of some neurologic conditions such as abductor spasmodic dysphonia. The anatomy of the nerve supply to the PCA is better understood than in previous eras, but the anatomical understanding has not translated to clinical application yet. Microscopic dissection allowed the identification and measurement of the branches from the recurrent laryngeal nerves (RLNs) to the PCA in 43 human cadaver larynges. The cricothyroid (CT) joint was the primary landmark for measurement. Other structural measurements were also made on the larynges. All of the PCA muscles received innervation from the anterior division of the RLN. The number of direct branches from the RLN ranged from 1 to 5 (average 2.3) More than 70% of PCA muscles also received 1-3 branches off of the branch to the interarytenoid (IA) muscle. Less than half of PCA muscles received any kind of nerve branches from the posterior division of the RLN. Branches to the PCA most commonly departed the main RLN in its vertical segment and all entered the muscle from its deep surface. All branches departed the RLN within an average of 9.5mm from the CT joint; the branch to the IA occurs distal to this point. The innervation to the PCA is complex and redundant, and the segment of the RLN supplying those branches is difficult to expose safely. For these reasons, selective denervation or reinnervation procedures limited to the nerve branches may be technically difficult. When needing only to denervate the PCA, this can be accomplished by removing a portion of the PCA and the underlying nerve supply. Surgical technique should be based upon the understanding of the anatomy of the PCA muscle and its nerve supply.

Refinements in modeling the passive properties of laryngeal soft tissue

The nonlinear viscoelastic passive properties of three canine intrinsic laryngeal muscles, the lateral cricoarytenoid (LCA), the posterior cricoarytenoid (PCA), and the interarytenoid (IA), were fit to the parameters of a modified Kelvin model. These properties were compared with those of the thyroarytenoid (TA) and cricothyroid (CT) muscles, as well as previously unpublished viscoelastic characteristics of the human vocal ligament. Passive parameters of the modified Kelvin model were summarized for the vocal ligament, mucosa, and all five laryngeal muscles. Results suggest that the LCA, PCA, and IA muscles are functionally different from the TA and CT muscles in their load-bearing capacity. Furthermore, the LCA, PCA, and IA have a much larger stress-strain hysteresis effect than has been previously reported for the TA and CT or the vocal ligament. The variation in this effect suggests that the connective tissue within the TA and CT muscles is somehow similar to the vocal ligament but different from the LCA, PCA, or IA muscles. Further demonstrating the potential significance of grouping tissues in the laryngeal system by functional groups in the laryngeal system was the unique finding that, over their working elongation range, the LCA and PCA were nearly as exponentially stiff as the vocal ligament. This paper was written in conjunction with an online technical report (http://www.ncvs.org/ncvs/library/tech) in which comprehensive muscle data and sensitivity analysis, as well as downloadable data files and computer scripts, are made available.

Electromyography of the cricoarytenoid unit during supracricoid laryngectomy with a cricohyoidoepiglottopexy procedure

Two patients who received supracricoid laryngectomy with cricohyoidoepiglottopexy to treat laryngeal cancers, underwent intra-operative electromyography analysis. After the lesion was removed and the electrodes were inserted into the remaining intrinsic laryngeal muscles, the depth of anaesthesia was carefully reduced. Gentle tactile stimulations were applied to the pharynx to trigger the reflex movement of the remaining arytenoids. Recordings were made when reflex movement was achieved. Case one: Electromyography (EMG) of the remaining arytenoid demonstrated clear phase differences indicating reciprocal activities between the adductor group (lateral cricoarytenoid muscle, interarytenoid muscle) and the abductor muscle (posterior cricoarytenoid muscle). Case two: EMG of the remaining arytenoid demonstrated reciprocal activities between the interarytenoid muscle and the posterior cricoarytenoid muscle. Activity of the lateral cricoarytenoid muscle was not evident because the muscle was excised during removal of the paraglottic space. Mobility of the arytenoid was attributed to interaction between the interarytenoid muscle and posterior cricoarytenoid muscle. Reciprocal interaction between the interarytenoid muscle and posterior cricoarytenoid muscle alone is also capable of maintaining post-operative laryngeal functions after supracricoid laryngectomy with cricohyoidoepiglottopexy.

Microsurgical anatomy of intralaryngeal distribution of the inferior laryngeal nerve

The functional results of a partial laryngeal surgery or a laryngeal reinnervation depend on the precise knowledge of the intra laryngeal anatomy of the inferior laryngeal nerve (ILN). Ten human larynges without known laryngeal disorders were obtained from human cadavers for ILN microdissection. Intra laryngeal ILN branching patterns were determined bilaterally. The lengths of the vertical, genu and oblique segments of the anterior division of ILN and the distance between the nerve within the paraglottic space and the cricothyroid articulation (CTA) were measured with a digital microcaliper. The mean lengths of the vertical, genu and oblique segments were 10.82, 5.89 and 9.29 mm, respectively. The mean distance between the nerve in the paraglottic space and the CTA was 11.20 mm. Key anatomical landmarks of the abductor division (vertical and genu segments of ILN) were the lateral border of posterior cricoarytenoid (PCA) muscle and the superior ligament of the CTA. The two-branch pattern for the lateral border of the PCA muscle has been the most frequent (50%). A branch of interarytenoid muscle (IA) originated from the genu segment. One or two branches for the PCA muscle has been identified in 75% of cases from the IA neural plexus on the front side of PCA muscle. The adductor division for the thyroarytenoid muscle and the lateral cricoarytenoid muscle was the oblique segment of the nerve. We conclude that abductor and adductor divisions of intra laryngeal ILN can be readily identified and the knowledge of key landmarks allows preservation of the ILN during partial surgery of the larynx and possibly selective muscle reinnervation.

Active and Passive Properties of Canine Abduction/Adduction Laryngeal Muscles

Active and passive characteristics of the canine adductor- abductor muscles were investigated through a series of experiments conducted in vitro. Samples of canine posterior cricoarytenoid muscle (PCA), lateral cricoarytenoid muscle (LCA), and interarytenoid muscle (IA) were dissected from dog larynges excised a few minutes before death and kept in Krebs-Ringer solution at a temperature of 37 degrees C +/- 1 degree C and a pH of 7.4 +/- 0.05. Active twitch and tetanic force was obtained in an isometric condition by applying field stimulation to the muscle samples through a pair of parallel-plate platinum electrodes. Force and elongation of the samples were obtained electronically with a dual-servo system (ergometer). The results indicate that the twitch contraction times of the three muscles are very similar, with the average of 32 +/- 1.9 ms for PCA, 29 +/- 1.6 ms for LCA, and 32 +/- 2.4 ms for IA across all elongations. Thus, PCA, LCA, and IA muscles are all faster than the cricothyroid (CT) muscles but slower than the thyroarytenoid (TA) muscles. The tetanic force response times of these muscles are also similar, with a maximum rate of force increase of 0.14 N/ms.

Findings of multiple muscle involvement in a study of 214 patients with laryngeal dystonia using fine-wire electromyography.

Although perceptual and stroboscopic data help in diagnosing and classifying laryngeal dystonia, these measures do not aid the voice clinician in targeting which specific muscles to treat with botulinum toxin. Most patients achieve smoother, less effortful voicing with standard injection regimens. However, there is a notable failure rate. We performed fine-wire electromyography on 214 consecutive patients with laryngeal dystonia. We correlated voice ratings, stroboscopy data, and fine-wire electromyography data. Videostroboscopy was successful in visually demonstrating most of the audible findings in isolated vocal tremor, but it was much less successful in identifying breaks alone or a combination of breaks and tremor. Fine-wire electromyography revealed that the thyroarytenoid muscle was significantly more likely than the lateral cricoarytenoid muscle to be the predominant muscle associated with adductor spasmodic dysphonia, and that the thyroarytenoid and lateral cricoarytenoid muscles were equally likely to be predominantly involved in tremor spasmodic dysphonia. In addition, several patients in both the adductor spasmodic dysphonia and the tremor spasmodic dysphonia groups presented with interarytenoid muscle predominance. All of the intrinsic laryngeal muscles are capable of being the predominant muscle in laryngeal dystonia, and there are patterns of muscle abnormalities that differ between adductor spasmodic dysphonia and tremor spasmodic dysphonia. Some of the failures in treating adductor spasmodic dysphonia with botulinum toxin, and the greater difficulty with success in treating patients with tremor spasmodic dysphonia, are due to failure to deliver toxin to the appropriate muscles.