Katsuhide Inagi

Sulcus vocalis: a rational analytical approach to diagnosis and management.

The term sulcus vocalis has been applied to a spectrum of disorders ranging from minor vocal fold indentations to destructive lesions causing severe dysphonia. To clarify the pathophysiology and to develop a more rational approach to treatment, we report a series of sulcus patients including 20 surgical cases. Clinical and histopathologic analysis produced a clinically useful classification: type 1 is a physiologic variant accentuated by atrophy but with intact lamina propria; types 2 (sulcus vergeture) and 3 (sulcus vocalis) are characterized by severe dysphonia, loss of vibratory activity, and destruction of the functional superficial lamina propria. These latter cases respond favorably to microsurgery designed to remove destroyed tissue, release scar contracture, and promote mucosal redraping by regional undermining. Further study of the extracellular matrix of the superficial lamina propria (Reinkes space) might indicate a common pathway in the pathogenesis of sulcus deformities and other related benign vocal fold lesions.

AN ANATOMIC STUDY OF THE RAT LARYNX : ESTABLISHING THE RAT MODEL FOR NEUROMUSCULAR FUNCTION

The gross and microscopic anatomy of the rat larynx was studied with particular attention to myology and neuromuscular structures to further validate it as a model to evaluate morphologic and functional changes induced by botulinum injection. A laryngeal alar cartilage (LAlC), alar cricoarytenoid (ACA) muscle, and a superior cricoarytenoid muscle (SCA) were identified as anatomic structures not previously described. Two portions (medial and lateral) of the thyroarytenoid muscle (TA) were distinguished. The function of the ACA was suggested to be similar to the aryepiglottis muscle in humans and the function of the SCA was suggested to be similar to the human interarytenoid muscle. The predominant pattern of motor endplate (MEP) distribution in rat laryngeal muscles (posterior cricoarytenoid, lateral cricoarytenoid, cricothyroid, and SCA) was to have MEPs concentrated mostly at the midbelly of muscle where they were distributed throughout the cross-sectional area of the midbelly. The TA and ACA differed from this pattern. The lateral TA had MEPs concentrated at the anterior third of its belly and those of the medial TA were located at the midbelly. Motor endplates in the ACA were located mostly at the posterior portion of muscle. Muscle fiber-typing showed subtle differences between the intrinsic laryngeal muscles. Fast fibers were predominant in the rat laryngeal muscles. This study supports the expanded use of rats in studies of laryngeal neuromuscular function and disease in humans.

Correlation Between Vocal Functions and Glottal Measurements in Patients With Unilateral Vocal Fold Paralysis

Observations and analysis of glottal characteristics are critical in choosing the best modality for surgery in patients with unilateral vocal fold paralysis (UVP). This study suggests that multiple glottal characteristics influence the vocal product in patients with UVP. In addition to the horizontal position of the paralyzed vocal fold (deviation from the midline), the glottal area, degree of bowing of the paralyzed and contralateral vocal folds, maximum separation between vocal folds, compensatory glottal maneuvers, and the vertical glottic closure plane significantly influenced the quality of the voice. Clinicians should be aware of these observations to facilitate treatment planning and assessment of the results of surgical procedures used to improve voice quality in cases of UVP.

Muscle fiber-type changes induced by botulinum toxin injection in the rat larynx.

This study examined muscle fiber-type alterations after single or multiple botulinum toxin (BT) injections to better understand possible morphologic changes induced by therapeutic BT injections in patients with spasmodic dysphonia. Muscle fiber staining was accomplished in rat intrinsic laryngeal muscles with antibodies to specific myosin heavy chains. Results indicated that the typical baseline distributions of type II muscle fibers (ie, types IIa, IIb, IIx, and IIL) were altered by BT injection, while no change was observed in type I fibers. Embryonic fibers were observed only along the needle insertion site at 7 days post BT injection. Although inferences from these animal data to human neuromuscular function must be made with caution, our findings provide insight into the possible cellular and molecular changes characterizing BT-injected muscles.

Analysis of factors affecting botulinum toxin results in spasmodic dysphonia

This study was designed to investigate how variations in patterns of injection could improve the efficacy of botulinum toxin injections in relieving the symptoms of adductor spasmodic dysphonia. A total of 64 adductor spasmodic dysphonia patients who were injected using indirect laryngoscopic localization (for a total of 426 injections) were analyzed retrospectively using their own subjective data on duration of voice improvement, optimal voice improvement, breathiness side effects, and intervals between treatments. Injection to both the thyroarytenoid (TA) and the lateral cricoarytenoid (LCA) simultaneously gave the best voice results; the overall improvement from baseline was the longest lasting, and the period during which the voice was the best was the longest lasting. TA+LCA also gave the shortest duration of undesirable breathiness side effect. On the basis of these data, it seems reasonable to recommend that initial botulinum toxin therapy for adductor spasmodic dysphonia patients should be a single unilateral injection placed strategically at the posterior portion of the TA and directed toward the LCA so that both muscle groups are affected.

The histologic fate of autologous collagen injected into the canine vocal fold

Collagen is a functionally essential component of the five-layered structure of the vocal fold. Soluble bovine collagen has previously been shown to be an effective injectable bioimplant for vocal fold defects, paralysis, and, especially, scarred larynges. Although bovine collagen appears to be well tolerated, the concern for possible adverse immunologic responses has deterred approval from the Food and Drug Administration for its clinical use in the larynx. Currently we are investigating the use of injectable autologous collagen for vocal fold augmentation. The purpose of this study is to examine the histologic fate of autologous collagen injected into the canine vocal fold at multiple intervals after injection. An ellipse of skin measuring 3 × 6cm was harvested from each of three dogs and processed into a naturally cross-linked injectable solution of collagen (Autologen). This autologous collagen was injected into one vocal fold and a control injection of buffer solution was injected contralaterally. The injections were well tolerated and no dog appeared to suffer any immediate or delayed ill effects. The dog larynges were harvested 1, 3, and 6 months after collagen injection and examined grossly and histologically. Injected autologous collagen material persisted in these experimental animals and appeared to be well tolerated. Based on this preliminary study, we anticipate autologous collagen to be at least as suitable as bovine chemically cross-linked collagen as an injectable bioimplant for vocal fold augmentation. It may also have the advantage of added safety and stability.

Efficacy of Repeated Botulinum Toxin Injections as a Function of Timing

This pilot study was designed to determine if the interval between repeated botulinum toxin injections influenced physiologic and histologic effects on laryngeal muscles in a rat model. The physiologic measurements included digitized videomicroscopic recording of vocal fold movement and electromyography. The histologic measurements included muscle fiber size and digitized optical density of laryngeal muscles after glycogen depletion by electrical stimulation. The results demonstrated that the effect of timing of the second injection was strongly correlated to laryngeal changes. Most notable were results in the subjects that underwent injections 6 weeks apart. We hypothesize that these findings might be related to terminal axonal sprouting with reinnervation. The results from this study help confirm and expand the validity of using the rat laryngeal model to understand the effect of botulinum toxin. Moreover, we believe that the data might be extrapolated to prove useful in predicting human responses to botulinum toxin treatment for functional dystonias such as spasmodic dysphonia.

Transoral Electromyographic Recordings in Botulinum Toxin—Injected Rat Larynges

Objective assessment of muscle function following botulinum toxin injections in laryngeal muscles is difficult in human subjects. We developed a rat laryngeal model for the study of botulinum toxin injection. A new laryngoscopic technique has made it possible to observe the rat larynx endoscopically and to obtain electromyographic measurements during and after injection of toxin. The electromyographic interference pattern, fibrillation potentials, and vocal fold movement were used for analyzing dose and volume effects of injected toxin. We conclude that the lowest dosage able to produce the maximal duration of functional laryngeal impairment is 0.07 U in a volume of 0.4 μL. This model will enable us to obtain physiologic and histologic parameters that can be used to assess the selection of optimal treatment regimens with botulinum toxin for the treatment of patients with spasmodic dysphonia.

Increased acute and chronic mitotic activity in rat laryngeal muscles after botulinum toxin injection

Objectives: To characterize the acute and chronic cellular effects of botulinum toxin (BT) injection into rat laryngeal muscles. A complete characterization of these effects is important because patients with focal dystonias of the head and neck are commonly treated with BT injection. Further, potential muscular changes in the larynx must be carefully delineated owing to the critical phonatory and airway protective functions of these muscles. Study Design: The acute and chronic cellular effects of BT injection were studied using 5′‐bromo 2′‐deoxyuridine (BrdU) following single and repeated BT injection into rat laryngeal muscles. BrdU is incorporated into mitotically active nuclei such that changes in cell proliferative behavior following BT injection can be monitored. Results: Increased mitotic activity was detected in the tissue samples studied following BT injection. Differences in the times of the peak distribution of BrdU‐labeled cells in each laryngeal muscle were observed. This may be related to the diffusion effects of BT. Prolonged muscle fiber changes, including splitting, were also observed as the result of repeated BT injection. Conclusions: The results of this study suggest that BT may induce a proliferative response in muscle tissue.

Electromyography in the laryngeal muscles of rat: Comparison between laryngeal muscles and limb muscle

There are many studies on the effect of botulinum toxin (BTX) in the rat model, but all use limb skeletal muscles. We could not find any articles that described the effect of BTX in rat laryngeal muscles. This paper reports the effect of BTX in thyroarytenoid (TA) muscles of the rat and the difference in tibialis anterior (AT) muscle. BTX effectiveness was evaluated by observing muscle movement and with monopolar needle electromyography (EMG). The interference pattern during respiratory activity was graded in the TA, and the presence of fibrillations determined in the TA and AT muscles every 2 to 3 days for 4 weeks after BTX injection. Different doses and volumes of BTX were prepared and similar doses and volumes of BTX were injected into both the TA and AT in each rat. The TA was injected using direct laryngoscopy. One day after BTX injection, the cords of the larynges that were injected with the largest doses and volumes were immobilized, foot movements were weakened, and the motor unit activation patterns of the TA muscle were decreased. These dysfunctions recovered between 10 days and 2 weeks after injection. The presence of fibrillations in injected TA and AT was observed 3 to 4 days after injection and continued for about 3 to 4 weeks. We believe that the rat larynx is a good model for the study of BTX effectiveness in spasmodic dysphonia because the short onset and short duration of the BTX effect should facilitate the study of altered injection parameters on the duration of BTX effectiveness.