Recurrent Laryngeal Neuropathy Research Articles

Equine laryngoplasty: Effects of three anchoring techniques in the muscular process and three positions for suture implantation in the cricoid cartilage.

To compare the effects of three anchoring techniques in the muscular process and three positions of laryngoplasty suture implantation in the cricoid cartilage on abduction of the arytenoid cartilage and interaction with the cricoarytenoid dorsalis (CAD) muscle compartments. Experimental study. Twenty-two cadaveric equine larynges. Three implantation techniques were assessed in the left muscular process. They were the use of a titanium corkscrew (CS), a standard caudal passage using a Jamshidi needle (JCa), and a standard cranial passage using a Jamshidi needle (JCr). Each was assessed in combination with three caudal locations in the cricoid cartilage (right, left, and left lateral). Each suture combination was tightened to submaximal abduction (Dixon grade 2). Force on the suture, degree of larynx caudal rotation, and CAD muscle indentation were evaluated. The force required for optimal arytenoid cartilage abduction was lower (p < .01) for constructs involving a CS (7.45 ± 4 N). The CS also resulted in lower (p < .01) CAD muscle indentation (2.01 ± 1.25 mm) and less larynx rotation (9 ± 3.87°; adjusted p < .05). When inserted into the muscular process at the CAD tendon insertion point, the biomechanical properties of the CS reduced the force required for optimal arytenoid cartilage abduction. The CS also minimized interference with the CAD muscle compartments and reduced caudal displacement of the left arytenoid cartilage when it was under suture tension. The CS implantation avoided larynx deformation and muscle interaction, offering the possibility to combine a nerve graft and laryngoplasty as a treatment for recurrent laryngeal neuropathy.

Unilateral laser ventriculocordectomy results in increased arytenoid stability in horses with severe left sided recurrent laryngeal neuropathy.

There is no objective information reporting the effect of unilateral laser ventriculocordectomy (VeC) on arytenoid abduction or stability. To evaluate arytenoid stability and abduction in horses with severe recurrent laryngeal neuropathy (RLN) before and after unilateral laser VeC. Prospective cohort. Eight horses with grade C or D exercising laryngeal function that underwent unilateral laser VeC were included. Exercising endoscopy was performed before and ≥6 weeks after left-sided laser VeC. Arytenoid stability at maximal exercise was calculated by measuring the left-to-right quotient angle ratio (LRQ) of the corniculate processes at the points of maximal arytenoid abduction (expiration) and maximal arytenoid collapse (inspiration). For each horse, means of measurements obtained for four breaths pre- and post-operatively were used for statistical analysis. The difference in LRQ between inspiration and expiration was lower post-operatively (median 0.039; interquartile range [IQR] 0.032-0.047) compared with pre-operatively (median 0.158; IQR 0.083-0.249; p = 0.01) confirming the left arytenoid was more stable following unilateral laser VeC. The degree of improvement was significantly greater for grade D horses compared with grade C horses (p = 0.04). The LRQ measured on maximal abduction was also lower post-operatively (median 0.467; IQR 0.444-0.506) compared with pre-operatively (median 0.578; IQR 0.554-0.655; p = 0.02) indicating the left arytenoid was less abducted following surgery. The sample size was small, no racehorses were included and post-operative assessment was conducted at a variable time after surgery. Unilateral laser VeC in grade C and D RLN-affected horses results in slightly reduced left arytenoid abduction but increased arytenoid stability.

Upper airway endoscopy in exercising horses: Findings in 164 barrel racing horses with respiratory clinical signs and/or poor performance

Barrel racing involves sprinting through a cloverleaf pattern in under 20 s. The prevalence of upper airway obstructions (UAO) in barrel racers is unknown, thus a retrospective analysis of 164 client-owned horses referred for overground endoscopy (OGE) between 2014 and 2022 was performed. Referring complaints included respiratory noise, cough, epistaxis, behaviour (owner reported stress/anxiety, refusal to enter arena, excessive head shaking), and/or poor performance. Horses performed a standardized exercise test with low and high-speed components. Videoendoscopic recordings were systematically scored by one experienced clinician. Exercising abnormalities included palatal instability (PI), intermittent dorsal displacement of the soft palate (iDDSP), nasopharyngeal collapse (NPC), recurrent laryngeal neuropathy (RLN), ventro-medial luxation of the apex of the corniculate process of the arytenoid (VLAC), medial deviation of the aryepiglottic fold (MDAF), vocal fold collapse (VFC), and cricotracheal ligament collapse. Associations between co-existing UAOs, age and sex were examined (McNemar’s test; logistic regression; P < 0.05). During exercise, 24/164 (15%) horses had no UAO. In the remaining 140 horses, 56% had two or more. NPC was observed in 68/140 (49%), PI in 59/140 (42%), iDDSP in 55/140 (39%), VFC in 38/140 (27%), RLN in 27/140 (19%), VLAC in 14/140 (10%), MDAF in 8/140 (6%) and cricotracheal ligament collapse in 8/140 (6%). Nasopharyngeal collapse and RLN were primarily Grade 3 and Grade B, respectively. Associations exist between several co-existing UAOs, but not age or sex. Abnormalities were more frequent at low-speed (55%) than high-speed (22%), highlighting the importance of OGEs at different exercise intensities. Multiple UAOs appear common in barrel racers with clinical presentations.

Prevalence of Exercise-Induced Pulmonary Hemorrhage, Tracheal Mucus and Recurrent Laryngeal Neuropathy in Competitive Draft Pulling Horses.

Respiratory disease is common in the horse population and is often be associated with poor performance in equine athletes. Despite their outstanding strength and aerobic capacity, little regard is given to draft horses and the respiratory disorders they may encounter when performing athletic activity. For this reason, the objectives of this study were: (1) to determine the prevalence of exercise-induced pulmonary hemorrhage (EIPH), tracheal mucus (TM) and recurrent laryngeal hemiplegia (RLH) in a population of competitive draft pulling horses, and (2) to determine if there was an association between horse weight, height, age, amount pulled, or competition placing with EIPH, TM or RLH in draft pullers. Results of this study identified EIPH in 26% of the study population, RLH in 32% and TM in 82% of participating horses; however, no risk factors were identified for the development of these problems in draft pulling horses.

Evaluation of recurrent laryngeal neuropathy in domestic and feral horse populations in Australia using histologic and immunohistochemical analysis: A pilot study.

Little is known about potential differences in the left recurrent laryngeal nerve (Lrln) and left cricoarytenoideus dorsalis (LCAD) muscle between domestic and feral horse populations. If a difference exists, feral horses may provide a useful control population for research related to recurrent laryngeal neuropathy (RLN) and increase our understanding of potential population pressures influencing the incidence RLN. The objective of this study was to compare the Lrln and LCAD of domestic and feral horses using histological and immunohistochemical techniques (IHC). Sixteen horses, domestic (n = 8) and feral (n = 8), without clinical or ancillary examinations that were processed at an abattoir had the Lrln and LCAD muscle harvested immediately following death. Carcass weights were recorded. Subjective and morphometric histologic assessment were performed on Lrln sections. The LCAD was assessed for myosin heavy chain (fibre type proportion, diameter and grouping using IHC. Fibre-type grouping consistent with RLN was seen in both groups. Regenerating fibre clusters were more common in domestic compared to feral horses (p = 0.04). No other histologic differences occurred between groups. Muscle fibre typing demonstrated a lower mean percentage of type IIX fibres in the feral group compared to the domestic group (p = 0.03). There was no difference in type I or IIA proportions or mean diameter of any fibre type between the groups. The domestic population showed evidence of nerve regeneration suggesting RLN in this group, yet this was not supported by the higher proportion of type IIX muscle fibres compared to the feral population. Further evaluation to clarify the significance and wider occurrence of the differences is indicated.

Three-dimensional models of the equine larynx can be used to perform traditional measures of arytenoid abduction and permit the positioning of modeled implants to demonstrate the anatomic feasibility of placing a rigid implant across the cricoarytenoid joint.

To develop 3D models of larynges to compare arytenoid abduction measurements between specimens and models, and to investigate the anatomic feasibility of placing an implant across the cricoarytenoid joint (CAJ) with or without arthrotomy. Cadaveric equine larynges (n = 9). Equine larynges underwent sequential CT scans in a neutral position and with 2 arytenoid treatments: bilateral arytenoid abduction (ABD) and bilateral arytenoid abduction after left cricoarytenoid joint arthrotomy (ARTH). Soft tissue, cartilage, and luminal volume 3-dimensional models were generated. Rima glottidis cross-sectional area (CSA) and left-to-right quotient (LRQ) angles were measured on laryngeal specimens and models. Arytenoid translation, articular contact area, and length of modeled implants placed across the CAJ were measured on models. Data were analyzed using paired t test or ANOVA and Tukey's post hoc test or non-parametric equivalents (P < .05). ARTH CSA was larger for laryngeal specimens than models (P = .0096). There was no difference in all other measures of CSA and LRQ angle between treatment groups or between specimens and models. There was no difference between ABD and ARTH groups for arytenoid cartilage translation, contact area, and implant length. The articular contact area was sufficient for modeled implant placement across the CAJ with a narrow range of implant lengths (17.59 mm to 23.87 mm) across larynges with or without arthrotomy. These results support further investigation of a CT-guided, minimally invasive surgical procedure. Future studies will evaluate the outcomes of the new procedure for technical precision, biomechanical stability, and post-operative success rates for horses with recurrent laryngeal neuropathy (RLN).

A biomechanical comparison of a novel two-loop suture technique and two sutures for laryngoplasty in the horse.

Evaluation of the strength of the novel suture technique by comparison with a 2-interrupted suture technique. 40 equine larynges. 40 larynges were used; 16 laryngoplasties were performed using the currently accepted 2-suture technique and 16 using the novel suture technique. These specimens were subjected to a single cycle to failure. Eight specimens were used to compare the rima glottidis area achieved with 2 different techniques. The mean force to failure, as well as the rima glottidis area of both constructs, were not significantly different. The cricoid width did not have a significant effect on the force to failure. Our results suggest that both constructs are equally strong and can achieve a similar cross-sectional area of the rima glottidis. Laryngoplasty ("tie-back") is currently the treatment of choice for horses with exercise intolerance due to recurrent laryngeal neuropathy. Failure to maintain the expected degree of arytenoid abduction post-surgery occurs in some horses. We believe this novel 2-loop pulley load-sharing suture technique can help achieve and, more importantly, maintain the desired degree of abduction during surgery.

Successful treatment of laryngeal dysplasia with ventriculocordectomy and prosthetic laryngoplasty in a horse

SummaryProsthetic laryngoplasty is a recognised treatment option for recurrent laryngeal neuropathy (RLN) in horses; however, there is no report of the use of laryngoplasty alone or in combination, as a successful treatment of equine laryngeal dysplasia. A 6‐year‐old Warmblood gelding was referred to the hospital for investigation of respiratory noise and exercise intolerance. Grade 4 recurrent laryngeal neuropathy and bilateral vocal fold collapse were diagnosed with overground endoscopy. Ultrasonography revealed laryngeal dysplasia. The horse underwent standing laser bilateral ventriculectomy, left vocal cordectomy, right vocal cordotomy and left‐sided laryngoplasty. Abnormal structural anatomy of the left aspect of the larynx consistent with laryngeal dysplasia was identified during surgery. Post‐operatively, the horse showed substantial clinical improvement with decreased respiratory noise and improved exercise capacity. Follow‐up overground endoscopy at 6 months post‐operative revealed Dixon grade 4 abduction of the left arytenoid cartilage. Follow‐up information via telephone conversation with the owner confirmed that the horse continued in active exercise with clinical improvement. This case report highlights the value of combined clinical, endoscopic and ultrasonographic examinations of the larynx in a horse with laryngeal dysplasia and concurrent grade 4 RLN and the successful surgical treatment achieved with combined bilateral ventriculectomy, left vocal cordectomy, right vocal cordotomy and prosthetic laryngoplasty.

Computational fluid dynamic analysis of upper airway procedures in equine larynges.

Computational fluid dynamics (CFD) has proven useful in the planning of upper airway surgery in humans, where it is used to anticipate the influence of the surgical procedures on post-operative airflow. This technology has only been reported twice in an equine model, with a limited scope of airflow mechanics situations examined. The reported study sought to widen this application to the variety of procedures used to treat equine recurrent laryngeal neuropathy (RLN). The first objective of this study was to generate a CFD model of an ex-vivo box model of ten different equine larynges replicating RLN and four therapeutic surgeries to compare the calculated impedance between these procedures for each larynx. The second objective was to determine the accuracy between a CFD model and measured airflow characteristics in equine larynges. The last objective was to explore the anatomic distribution of changes in pressure, velocity, and turbulent kinetic energy associated with the disease (RLN) and each surgical procedure performed. Ten equine cadaveric larynges underwent inhalation airflow testing in an instrumented box while undergoing a concurrent computed tomographic (CT) exam. The pressure upstream and downstream (outlet) were measured simultaneously. CT image segmentation was performed to generate stereolithography files, which underwent CFD analysis using the experimentally measured outlet pressure. The ranked procedural order and calculated laryngeal impedance were compared to the experimentally obtained values. The CFD model agreed with the measured results in predicting the procedure resulting in the lowest post-operative impedance in 9/10 larynges. Numerically, the CFD calculated laryngeal impedance was approximately 0.7 times that of the measured calculation. Low pressure and high velocity were observed around regions of tissue protrusion within the lumen of the larynx. RLN, the corniculectomy and partial arytenoidectomy surgical procedures exhibited low pressure troughs and high velocity peaks compared to the laryngoplasty and combined laryngoplasty/corniculectomy procedures. CFD modeling of the equine larynx reliably calculated the lowest impedance of the different surgical procedures. Future development of the CFD technique to this application may improve numerical accuracy and is recommended prior to consideration for use in patients.

Computed tomographic geometrical analysis of surgical treatments for equine recurrent laryngeal neuropathy.

To characterize the 3-D geometry of the equine larynx replicating laryngeal hemiplegia and 4 surgical interventions by use of CT under steady-state airflow conditions. Secondly, to use fluid mechanic principles of flow through a constriction to establish the relationship between measured airflow geometries with impedance for each surgical procedure. 10 cadaveric horse larynges. While CT scans were performed, inhalation during exercise conditions was replicated for each of the following 5 conditions: laryngeal hemiplegia, left laryngoplasty with ventriculocordectomy, left laryngoplasty with ipsilateral ventriculocordectomy and arytenoid corniculectomy, corniculectomy, and partial arytenoidectomy for each larynx while CT scans were performed. Laryngeal impedance was calculated, and selected cross-sectional areas were measured along each larynx for each test. Measured areas and constriction characteristics were analyzed with respect to impedance using a multilevel, mixed-effects model. Incident angle, entrance coefficient, outlet coefficient, friction coefficient, orifice thickness, and surgical procedure were significantly associated with upper airway impedance in the bivariable model. The multivariate model showed a significant influence of incident angle, entrance coefficient, and surgical procedure on impedance; however, the orifice thickness became nonsignificant within the model. Laryngeal impedance was significantly associated with the entrance configuration for each procedure. This suggested that the equine upper airway, despite having a highly complex geometry, adheres to fluid dynamic principles applying to constrictions within pipe flow. These underlying flow characteristics may explain the clinical outcomes observed in some patients, and lead to areas of improvement in the treatment of obstructive upper airway disease in horses.

Vocal Fold Paralysis Following COVID-19 Vaccination: Query of VAERS Database

ObjectiveVocal fold paresis or paralysis (VFP) may severely affect quality of life due to dysphonia and respiratory distress. As an increasing percentage of the United States population receives the COVID-19 vaccination, the objective of this study is to determine the correlation of COVID-19 postvaccination recurrent laryngeal neuropathy and resulting VFP.MethodsThe Vaccine Adverse Event Reporting System database was queried for patients exhibiting symptoms of VFP following COVID-19 vaccination. Patient demographics and clinical information including presenting symptoms, time of symptom onset, time of diagnosis and laterality.ResultsTwenty patients were found to have laryngoscopy confirmed VFP following COVID-19 vaccination. Vaccinations for Pfizer-BioNTech, Moderna, and Janssen were reported. Of those reported, 13 patients were female (65.0%) and seven were male (35.0%), with a mean age of 61.8 years. The most common presenting symptom was a hoarse voice (30.0%). A majority of these cases were unilateral in nature (64.0%). Mean time from vaccination to symptom onset was 12.1 days and mean time from vaccination to diagnosis was 37.6 days.ConclusionFor patients presenting with voice or swallowing complaints after receiving the COVID-19 vaccine, prompt evaluation by an otolaryngologist should occur. However, the potential VFP side effect of vaccination is very rarely cited in the literature and largely outweighed by the benefits of vaccination. Further research is needed to delineate the exact pathophysiology of this complication and determine whether a causal relationship exists.

The impact of grade of laryngeal function immediately prior to laryngoplasty and ipsilateral ventriculocordectomy on postoperative performance: 623 Thoroughbred racehorses (1998-2013).

There is persistent concern among some trainers, owners and veterinarians regarding the effect of preoperative laryngeal function grade on the outcome of laryngoplasty and ventriculocordectomy (LPVC). To determine the effect of laryngeal function grade prior to LPVC on postoperative performance. Retrospective case-series. Medical and race records of Thoroughbred racehorses diagnosed with recurrent laryngeal neuropathy (RLN) and treated with LPVC between 1998 and 2013 were reviewed. Horses were placed into three groups based on preoperative laryngeal function grade (grade III.1, grades III.2/III.3, and grade IV). The effect of preoperative laryngeal function grade on postoperative performance was determined by multivariable logistic regression, Cox proportional hazard model and multivariable linear regression analysis. In a multivariable logistic regression, grade III.2/III.3 horses had 1.88 times higher odds (95% CI=1.03-3.43) of racing after LPVC than grade IV (P=.04). A multivariable Cox's proportional hazard analysis controlling for race prior to surgery (P<.01) showed that likelihood of racing postoperatively was not different between grade III.1 and grade IV (P=.6), and although not statistically significant, there was a tendency for grades III.2/III.3 to be more likely to race postoperatively than horses with grade IV (P=.07). Kaplan-Meier survival analysis showed that grade IV horses took a longer time to race compared with grade III.1 and grade III.2/III.3. Laryngeal function grade did not influence the mean earnings per start. The small number of horses in the grade III.1 group compared with the III.2/III.3 and IV groups influenced the effect of grade III.1 on outcome. Laryngeal function grade may affect likelihood of racing after LPVC, but not earnings per start. Grade III. 2/III.3 horses were more likely to race postoperatively than grade IV horses, and grade IV horses took a longer time to first race after LPVC.

Diagnosis of upper respiratory tract disorders in horses using a cheap, flexible and steerable borescope

Background: Endoscopy is essential for the diagnosis of upper respiratory tract (URT) disorders in horses but equipment is expensive and therefore not always available. An industrial borescope might be a cheap alternative to visualize the URT. Objectives: To investigate the applicability of a smartphone-connected flexible and steerable borescope to perform URT endoscopy in horses. Study design: Prospective descriptive study. Methods: In horses with a clinical indication, endoscopy was first performed with a borescope (Mini Endoscope Camera 360° Steering 720P Borescope 8mm USB car Pipe inspection Camera; approximately 300 euros) and subsequently with a veterinary endoscope (TXHD136-9D, Dr. Fritz, Germany), which was used as gold standard. Typical URT structures of interest (depending on clinical signs) were digitally recorded. Recordings of both examinations were reviewed by a blinded observer. Results: One hundred horses underwent both endoscopic examinations via the right (n=100) and left (n=24) nasal passage. In 81/83 attempts, the ethmoid and sinus opening were visualized on the right side and in 22/24 attempts on the left side. Pharyngeal and laryngeal structures could always be visualized except in 6 horses where the tip of the epiglottis could not be seen due to technical failure of the steering mechanism. In 66/72 attempts, the trachea could be visualized proximally, of which 59 all the way until the carina. Borescope and endoscope grading scores for pharyngeal lymphoid hyperplasia, recurrent laryngeal neuropathy and tracheal mucus were identical in 88/100, 93/100 and 48/59 horses, respectively. The remainder differed only one (sub)grade. The borescope was replaced halfway the study as the steering mechanism started to fail after 45 to 50 examinations. Main limitations: A wide range of borescopes exist but only one type was tested. Conclusions: A flexible, steerable borescope, connected to a smartphone, provides a cheap alternative to perform URT endoscopy in horses.

Diagnosis of upper respiratory tract disorders in horses using a cheap, smartphone‐connected, flexible and steerable borescope

SummaryBackgroundEndoscopy is essential for the diagnosis of upper respiratory tract (URT) disorders in horses but equipment is expensive. An industrial borescope might be used to visualise the URT when an endoscope is not available.ObjectivesTo investigate the applicability of a cheap, smartphone‐connected, flexible and steerable borescope to perform URT endoscopy in horses.Study designProspective descriptive study.MethodsIn horses with a clinical indication, endoscopy was first performed with a borescope and subsequently with a veterinary endoscope, which was used as gold standard. Typical URT structures of interest (depending on clinical signs) were digitally recorded. Recordings of both examinations were reviewed by a blinded observer.ResultsOne hundred horses underwent both endoscopic examinations via the right (n = 100) and left (n = 24) nasal passage. In 81/83 attempts, the ethmoidal labyrinth and sinus ostia were visualised on the right side and in 22/24 attempts on the left side. Pharyngeal and laryngeal structures could always be visualised except in 6 horses where the tip of the epiglottis could not be seen due to technical failure of the steering mechanism. In 66/72 attempts, the trachea could be visualised proximally, of which the carina was visualised in 59. Borescope and endoscope grading scores for pharyngeal lymphoid hyperplasia, recurrent laryngeal neuropathy and tracheal mucus were identical in 88/100, 93/100 and 48/59 horses, respectively. The remainder differed only one or two subgrades. The borescope was replaced halfway through the study as the steering mechanism started to fail after 45 to 50 examinations.Main limitationsLack of reliability and the absence of a working channel of this particular borescope model.ConclusionsA flexible, steerable borescope, connected to a smartphone, allows visualising specific parts of the URT in horses.

Development of a constant pressure perfused ex vivo model of the equine larynx.

Distal axonopathy is seen in a broad range of species including equine patients. In horses, this degenerative disorder of the recurrent laryngeal nerve is described as recurrent laryngeal neuropathy (RLN). The dysfunctional innervation of the cricoarytenoideus dorsalis muscle (CAD) leads to a loss of performance in affected horses. In general, ex vivo models of the larynx are rare and for equine patients, just one short report is available. To allow for testing new therapy approaches in an isolated organ model, we examined equine larynges in a constant pressure perfused setup. In order to check the vitality and functionality of the isolated larynx, the vessels´ reaction to norepinephrine (NE) and sodium nitroprusside (NP) as vasoactive agents was tested. Additionally, the contractility of the CAD was checked via electrical stimulation. To determine the extent of hypoxic alterations, lactate dehydrogenase (LDH) and lactate were measured and an immunofluorescent analysis of hypoxia-inducible factor (HIF-1α), a key transcription factor in hypoxia, was performed. For this, a hypoxia-induced cell culture for HIF-1α was developed. The application of NE led to an expected vasoconstriction while NP caused the expected vasodilation. During a perfusion period of 352 ±20.78 min, LDH values were in the reference range and lactate values slightly exceeded the reference range at the end of the perfusion. HIF-1α nuclear translocation could reliably be detected in the hypoxia-induced cell cultures, but not in sections of the perfused CAD. With the approach presented here, a solid basis for perfusing equine larynges was established and may serve as a tool for further investigations of equine larynx disorders as well as a transferrable model for other species.

Evaluation of Overground Endoscopy Findings in Colombian Criollo Paso Horses

The dynamic upper airway functional (URT) problems of Colombian paso horses (CPH) have not been investigated in literature up to date. These horses perform special walking gaits with high poll flexion of the neck. Our goal is to evaluate the upper airway mechanics in CPH, showing abnormal respiratory sounds and poor performance during exercise. Resting and overground endoscopy was performed in 40 CPHs. Statistical analyses were performed using the sciPy package. One-tailed Fisher exact tests were used to check for positive contingency between each pair of upper respiratory tract disorder (P < .05). Arytenoid cartilage collapse was observed in 35 of 40 cases during exercise. Among these, dynamic laryngeal collapse (DLC) was the most significant finding, but ventromedial luxation of the apex of the corniculate process of the arytenoid and recurrent laryngeal neuropathy was also observed. Dorsal displacement of the soft palate was only detected in 4 of 40 cases. DLC was significantly associated with vocal cord collapse, nasopharyngeal collapse, and medial collapse of the margins of the epiglottis, and medial collapse of the margins of the epiglottis was associated with nasopharyngeal collapse. DLC is only a typical feature in some special breeds worldwide. We suggest that the extensive poll flexion and the relatively small laryngeal lumen and high intensitivity workload are the most important predisposing factors of DLC. Ventromedial luxation of the apex of the corniculate process of the arytenoid was over-represented in our caseload, compared with other studies. Whereas, despite the intensive workload, dorsal displacement of the soft palate was relatively uncommon. We presume that this could also be tailored to the high poll flexion performed during the special gaits.

Immunohistochemical analysis of laryngeal muscle of horses clinically affected with recurrent laryngeal neuropathy.

As myosin heavy chain (MyHC) profile of muscle fibres is heavily influenced by neural input, changes in MyHC expression are expected in horses clinically affected with recurrent laryngeal neuropathy (RLN) yet, this has not been thoroughly investigated. To describe the changes in MyHC and fibre diameter in left cricoarytenoideus dorsalis (L-CAD) muscle of horses with clinical signs of RLN. Observational cohort study. Immunohistochemistry was used to assess the MyHC-based fibre-type proportion, size and grouping in the L-CAD of 10 Thoroughbred horses, five clinically affected with RLN and five unaffected controls based on resting endoscopic examination. The Mann-Whitney U test was used to compare the two groups. Compared to controls (of mean age 3.0±1.7years) which only expressed type I, IIA and IIX MyHC, the L-CAD of affected horses (of mean age 2.8±0.8years) had obvious fibre-type grouping, and despite apparent compensatory hypertrophy of a small number of fibres, a decrease in overall fibre diameter (median difference -35.2µm, 95% CI -47.4 to -7.9, P=.02) and diameter of type IIA fibres (median difference -46.8µm, 95% CI -52.1 to -5.0, P=.03) was observed. Anti-fast MyHC (MY32) cross-immunoreacted with embryonic-MyHC. Whereas MY32-positive fibres were identified as type IIX in controls, in affected horses these fibres were less than 50µm diameter with internal nuclei and were MYH3-positive for embryonic myosin indicating depletion of type IIX fibres, yet active regeneration and fibre renewal. Small sample size that did not include subclinical cases. Fibre size and appearance rather than staining colour were relied upon to differentiate embryonic from type IIX MyHC. Horses clinically affected with RLN have overall atrophy of fibres, loss of IIX fibres and expression of embryonic myosin indicating regenerative capacity. Despite hypertrophy of some remaining fibres, the overall decline in the bulk of fibres, including those most fatigue-resistant, may be the critical change that results in failure to maintain arytenoid abduction during exercise although direct comparison to subclinical cases is needed to confirm this.

Endoscopic recurrent laryngeal neuropathy grade prevalence in a sample of thoroughbred yearlings at public auction in South Africa (2013-2019).

Endoscopy of thoroughbred (TB) yearlings at public auctions is common in South Africa. Laryngeal function (LF) is a common concern of buyers of young TBs. Cancellation of sale because of LF abnormalities is a concern for both the vendor and the buyer, with recurrent laryngeal neuropathy (RLN) being a common cause of sale cancellation. The aim of this descriptive study was to determine the prevalence of RLN at South African premier TB yearling sales. This study was designed as a retrospective descriptive analysis of upper respiratory tract (URT) endoscopic examinations to determine RLN grade, performed at two premier TB yearling sales in South Africa. Results of buyer-requested endoscopic examination from 2013 to 2019 were included. Results from the yearling sales were analysed for prevalence of RLN grade (using Rakestraw’s 4-point system) and compared to similar previously published studies. For analysis of effects of gender on RLN grading, horses were grouped and Fisher’s exact test was used to determine if there was a relationship between gender and grade. For comparison of the effects of age on grade, and sales year on grade, a Kruskal–Wallis test was conducted. A value of p < 0.05 was considered significant. A total of 858 horses were examined out of 4149 offered for sale; there were 57.58% colts and 42.42% fillies (mean age of 18.1 months). The annual percentage for grade 1 was 84.04% ± 9.98%, for grade 2: 14.49% ± 10.69%, for grade 3: 0.71% ± 0.57% and for grade 4: 0.76% ± 0.94%. There were no other significant findings. The exclusive nature of the sale and the increasing proclivity for pre-sale scoping may have skewed the results. This study shows that RLN grade incidences in TB yearlings at public auctions in South Africa are as follows: grade 1: 84.04%, grade 2: 14.49%, grade 3: 0.71% and grade 4: 0.76%. The results were similar to that of an adult population of horses examined in South Africa in a previous study.

External transcutaneous ultrasound technique in the equine cricoarytenoideus dorsalis muscle: Assessment of muscle size and echogenicity with resting endoscopy.

Recent studies have assessed the cricoarytenoideus dorsalis muscle (CAD) using transoesophageal ultrasonography in equine recurrent laryngeal neuropathy (RLN). We assessed the CAD using the external transcutaneous ultrasound technique, which may constitute an easier method in horses. To evaluate ultrasonographic imaging of the left cricoarytenoideus dorsalis muscle (LCAD) and right cricoarytenoideus dorsalis muscle (RCAD) as a diagnostic tool for RLN using the transcutaneous ultrasound technique. Cross-sectional study. The axial plane thickness, cross-sectional area and echogenicity of the LCAD and RCAD were measured using transcutaneous ultrasonography in 164 horses. Assessments of LCAD were compared with those of RCAD. The LCAD:RCAD ratios in thickness and area were compared between control horses (resting grades 1 and 2) and horses with resting laryngeal grades 3 and 4 using the Havemeyer 4-point grading system with subgrades. The LCAD:RCAD ratios for thickness and area were 0.69 and 0.66 in horses with resting grades 3 and 4 respectively; LCAD was more hyperechogenic than RCAD in resting grades 3 and 4. LCAD:RCAD ratios for thickness and area in grades 3.II, 3.III and 4 were significantly lower than those in control horses. Thickness and area of the LCAD were negatively correlated with resting laryngeal grade MAIN LIMITATIONS: Overground endoscopy was not performed in this study. There were some differences in methodology: measurement of the physical thickness of the LCAD and clipping of hair at the laryngeal region were only performed in horses that underwent laryngoplasty. Results of ultrasonographic assessments of the CAD using transcutaneous ultrasonography were similar to those obtained by transoesophageal ultrasonography. This technique enables a simple, noninvasive, direct and easy examination. Assessment of the CAD using transcutaneous ultrasonography may be a useful technique and a potential option for determining whether to perform nerve graft or laryngoplasty.

Assessing pathological changes within the nucleus ambiguus of horses with recurrent laryngeal neuropathy: An extreme, length-dependent axonopathy.

Equine recurrent laryngeal neuropathy (RLN) is a naturally occurring model of length-dependent axonopathy characterized by asymmetrical degeneration of recurrent laryngeal nerve axons (RLn). Distal RLn degeneration is marked, but it is unclear whether degeneration extends to include cell bodies (consistent with a neuronopathy). With examiners blinded to RLN severity, brainstem location, and side, we examined correlations between RLN severity (assessed using left distal RLn myelinated axon count) and histopathological features (including chromatolysis and glial responses) in the nucleus ambiguus cell bodies, and myelinated axon count of the right distal RLn of 16 horses. RLN severity was not associated with RLn cell body number (P > .05), or degeneration. A positive correlation between the left and right distal RLn myelinated axon counts was identified (R2 = 0.57, P < .05). We confirm that RLN, a length-dependent distal axonopathy, occurs in the absence of detectable neuronopathy.