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

Introduction: 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. Methods: 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. Results and discussion: 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.

Genetics of Equine Respiratory Disease.

Genetic factors influence the development of guttural pouch tympany, recurrent laryngeal neuropathy, severe equine asthma, exercise-induced pulmonary hemorrhage, and possibly also some malformations and infectious diseases of the respiratory tract. The current data suggest that most of these diseases are complex, resulting from the interaction between several genes and environmental factors. To date, no specific genes or causative mutations have been identified that would allow the development of practical genetic tests. In the future, genetic profiling panels, based on multiple genetic markers and environmental risk factors, may allow identification of individuals with an increased genetic risk.

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.

BACKGROUND: 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. OBJECTIVES: 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. STUDY DESIGN: Cross-sectional study. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Exercising upper respiratory videoendoscopic findings of 50 competition draught horses with abnormal respiratory noise and/or poor performance.

BACKGROUND: Upper respiratory tract (URT) endoscopy at rest is commonly used to evaluate competition draught horses with URT conditions. Overground endoscopy might be preferred for draught horse URT evaluation as it allows the horses to be driven with harness, overcheck and cart-load under similar conditions to those experienced in the show ring where airway conditions are most prominent. OBJECTIVE: To describe the exercising URT findings of competition draught horses with abnormal respiratory noise and/or poor performance. STUDY DESIGN: Case series. METHODS: Medical records of competition draught horses undergoing overground endoscopic evaluation between January 2013 and January 2018 with a presenting complaint of abnormal respiratory noise and/or poor performance were reviewed. Video recordings of resting and overground endoscopy were evaluated in all horses. Spearman's rank correlation coefficient was calculated between laryngeal function at rest and at exercise. RESULTS: Fifty competition draught horses were examined. Thirteen had previously undergone URT surgery. There was significant correlation between resting and exercising laryngeal function (ρ = 0.77, P<0.01). Abnormalities were detected in 46 horses and included arytenoid cartilage collapse (n = 31), vocal fold collapse (n = 27), palatal dysfunction (n = 14), epiglottic disorders (n = 11), dynamic laryngeal collapse (n = 1), rostral deviation of the palatopharyngeal arch (n = 3) and medial deviation of the aryepiglottic folds (n = 16). The majority of horses had a complex of abnormalities (n = 31) or required exercising examination for identification (n = 41). Incidental upper oesophageal incompetence was observed in nine horses. MAIN LIMITATIONS: Retrospective collection of data. CONCLUSIONS: Overground endoscopic evaluation was a useful technique for identifying URT disorders in competition draught horses. The spectrum of upper airway conditions identified in exercising draught horses supports the use of overground endoscopy as a diagnostic technique and could influence treatment considerations. The Summary is available in Portuguese - see Supporting Information.

Meta-analysis evaluating resting laryngeal endoscopy as a diagnostic tool for recurrent laryngeal neuropathy in the equine athlete.

BACKGROUND: Resting endoscopy has commonly been used as a method to predict laryngeal function at exercise. OBJECTIVES: To perform a meta-analysis to determine the sensitivity and specificity of resting laryngeal endoscopy to predict clinical recurrent laryngeal neuropathy at exercise. STUDY DESIGN: Meta-analysis. METHODS: Manuscripts were included if data were available for both resting and exercising airway function on all or a subset of horses. Normal resting endoscopy was defined as laryngeal grades 1 or 2 on a 4-/7-point scale or 1, 2 or 3 on a 5-point scale and normal dynamic endoscopy as a dynamic laryngeal grade A. RESULTS: Twelve studies including 1827 horses were evaluated. A small proportion of horses with grade 1 or grade 2 laryngeal function at rest, 3.5 and 11.9%, respectively, were identified as having abnormal laryngeal function at exercise. Within the horses with grade 3 laryngeal function at rest, 16% were classified as grade A, 26.4% as grade B and 57.6% as grade C at exercise. Worsening subgrades within resting grade 3 demonstrated an increasing proportion of complete or partial paralysis at exercise. The sensitivity and specificity of resting endoscopy was 74.4 and 95.1%, respectively, and the positive and negative predictive values were 85.6 and 90.5% respectively. MAIN LIMITATIONS: Use of two separate grading systems for evaluating resting laryngeal function. Other forms of dynamic airway collapse were not evaluated. CONCLUSIONS: Resting endoscopy is sensitive and highly specific for predicting laryngeal function at exercise. Dynamic endoscopy is important to assess multiple causes of airway collapse.

Exploratory factor analysis of signalment and conformational measurements in Thoroughbred horses with and without recurrent laryngeal neuropathy.

BACKGROUND: Conflicting results have been reported for risk factors for recurrent laryngeal neuropathy (RLN) based on resting endoscopic evaluation and comparison of single conformation traits, with many traits correlated to one another. OBJECTIVES: To simplify identification of signalment and conformation traits (i.e. variables) associated with RLN cases and controls diagnosed with exercising overground endoscopy (OGE) using exploratory factor analysis (EFA). STUDY DESIGN: Prospective cohort. METHODS: Pearson's rank correlation was used to establish significance and association between variables collected from n = 188 Thoroughbreds from one stable by observers blinded to OGE results. Exploratory factor analysis was conducted on nine variables for cases and controls; common elements between variables developed a factor, with variables grouped into three factors for cases and controls respectively. Correlation (loading) between each variable and factor was calculated to rank relationships between variables and cases/controls, with factors retrospectively named based on their underlying correlations with variables. RESULTS: Numerous inter-correlations were present between variables. Most strongly correlated in cases were wither height with body weight (r = 0.70) and ventral neck length (r = 0.68) and in controls body weight with rostral neck circumference (r = 0.58). Wither height (r = 0.61) significantly loaded the top-ranked factor for cases ('heightRLN '), explaining 25% of conformational variance. Ventral neck length (r = 0.69) and age (r = 0.57) significantly loaded the second-ranked factor for cases ('neck lengthRLN '), explaining 16% of conformational variance. Rostral neck circumference (r = 0.86) and body weight (r = 0.6) significantly loaded the top-ranked factor for controls ('body sizeCON '), explaining 19% of the variance. Wither height (r = 0.84) significantly loaded the second-ranked factor for controls ('heightCON '), explaining 13% of the variance. MAIN LIMITATIONS: Horses had not reached skeletal maturity. CONCLUSIONS: Exploratory factor analysis allowed weightings to be determined for each variable. Wither height was the predominant conformational feature associated with RLN. Exploratory factor analysis confirms aggregated conformational differences exist between RLN cases and controls, suitable for future evaluations.

Identification of loci affecting sexually dimorphic patterns for height and recurrent laryngeal neuropathy risk in American Belgian Draft Horses.

Equine recurrent laryngeal neuropathy (RLN) is a bilateral mononeuropathy with an unknown etiology. In Thoroughbreds (TB), we previously demonstrated that the haplotype association for height (LCORL/NCAPG locus on ECA3, which affects body size) and RLN was coincident. In the present study, we performed a genome-wide association scan (GWAS) for RLN in 458 American Belgian Draft Horses, a breed fixed for the LCORL/NCAPG risk alelle. In this breed, RLN risk is associated with sexually dimorphic differences in height, and we identified a novel locus contributing to height in a sex-specific manner: MYPN (ECA1). Yet this specific locus contributes little to RLN risk, suggesting that other growth traits correlated to height may underlie the correlation to this disease. Controlling for height, we identified a locus on ECA15 contributing to RLN risk specifically in males. These results suggest that loci with sex-specific gene expression play an important role in altering growth traits impacting RLN etiology, but not necessarily adult height. These newly identified genes are promising targets for novel preventative and treatment strategies.

Pathological classification of equine recurrent laryngeal neuropathy.

Recurrent Laryngeal Neuropathy (RLN) is a highly prevalent and predominantly left-sided, degenerative disorder of the recurrent laryngeal nerves (RLn) of tall horses, that causes inspiratory stridor at exercise because of intrinsic laryngeal muscle paresis. The associated laryngeal dysfunction and exercise intolerance in athletic horses commonly leads to surgical intervention, retirement or euthanasia with associated financial and welfare implications. Despite speculation, there is a lack of consensus and conflicting evidence supporting the primary classification of RLN, as either a distal ("dying back") axonopathy or as a primary myelinopathy and as either a (bilateral) mononeuropathy or a polyneuropathy; this uncertainty hinders etiological and pathophysiological research. In this review, we discuss the neuropathological changes and electrophysiological deficits reported in the RLn of affected horses, and the evidence for correct classification of the disorder. In so doing, we summarize and reveal the limitations of much historical research on RLN and propose future directions that might best help identify the etiology and pathophysiology of this enigmatic disorder.

Modified first or second cervical nerve transplantation technique for the treatment of recurrent laryngeal neuropathy in horses.

BACKGROUND: In horses, the only established method for reinnervation of the larynx is the nerve-muscle pedicle implantation, whereas in human medicine, direct nerve implantation is a standard surgical technique for selective laryngeal reinnervation in human patients suffering from bilateral vocal fold paralysis. OBJECTIVES: (1) To describe a modified first or second cervical nerve transplantation technique for the treatment of recurrent laryngeal neuropathy (RLN) in horses and (2) evaluate the outcomes of reinnervation using direct nerve needle-stimulation of the first cervical nerve and exercising endoscopy before and after surgery. STUDY DESIGN: Case series. METHODS: Nerve transplantation surgery, in which the first or second cervical nerve is tunnelled through the atrophied left cricoarytenoideus dorsalis muscle, was performed in combination with ipsilateral laser ventriculocordectomy. Ultrasound-guided stimulation of the first cervical nerve at the level of the alar foramen was used to confirm successful reinnervation post-operatively. Exercising endoscopy was performed before and after surgery. The exercising RLN grade of the left arytenoid was blindly determined at the highest stride frequency for each examination. RESULTS: Surgery was performed in 17 client-owned animals with RLN. Reinnervation was confirmed by nerve stimulation and subsequent arytenoid abduction observed in 11 out of 12 cases between 4 and 12 months post-operatively. Fourteen horses had exercising endoscopy before and after surgery. Nine horses had an improved exercising RLN grade, four horses had the same exercising grade and one horse had a worse exercising grade after surgery. MAIN LIMITATIONS: A sham-operated control group was not included and follow-up beyond 12 months and objective performance data were not obtained. CONCLUSIONS: The modified first or second cervical nerve transplantation technique, using tunnelling and direct implantation of the donor nerve into the cricoarytenoideus dorsalis muscle, resulted in reinnervation in 11 out of 12 cases and improved exercising grade in 9 out of 14 horses within 12 months after surgery.

Fifty years of recurring struggles with recurrent laryngeal neuropathy.

Recurrent laryngeal neuropathy appears to be a simple problem that should have a simple solution, yet the complexity and dynamic nature of laryngeal function is underappreciated. This review highlights the challenges and accomplishments that work towards that greater understanding of what is necessary to find a successful solution.

Aryepiglottic fold augmentation as treatment for late-onset dysphagia following surgical treatment of recurrent laryngeal neuropathy.

OBJECTIVE: Coughing and dysphagia have been described following prosthetic laryngoplasty (LP) with or without ventriculectomy/ventriculocordectomy (VE/VCE) for the treatment of recurrent laryngeal neuropathy. All previous case descriptions include patients with acute onset of clinical signs after surgery that persisted. The authors observed a late-onset of dysphagia and coughing months to years after LP ± VE/VCE. The condition was always associated with an abnormality of the aryepiglottic fold (AEF). Treatment options for those patients are limited. We suggest augmentation of the AEF as treatment for affected horses. The goal of the study was two-fold: Firstly, to describe a new condition of late-onset dysphagia in horses following LP ± VE/VCE associated with an abnormal appearance of the AEF, and secondly, to offer a minimally invasive and successful treatment for those patients. MATERIAL AND METHODS: Six horses were presented because of dysphagia and coughing with an onset of months to years after LP ± VE/VCE. Endoscopically, the AEF always appeared thinner and more flaccid to a varying degree. The food path was traceable along the AEF into the trachea using dyed molasses. An initial injection of hyaluronic acid (HA) into the AEF led to immediate improvement of the dysphagia. The procedure was performed in the standing sedated horse. The needle was placed through the cricothyroid ligament and the injection performed under endoscopic guidance. RESULTS: All horses tolerated the injection well. Injection of HA was successful only in the short term in all cases and repeated injections were needed for permanent resolution using either cross-linked HA, polyacrylamide hydrogel or platelet rich plasma. CONCLUSION AND CLINICAL RELEVANCE: Horses may develop dysphagia and coughing months to years after LP ± VE/VCE as a late-onset complication. The condition seems to be associated with an abnormal appearance and function of the AEF. Successful treatment is possible by augmenting the AEF. However, careful patient selection is mandatory.

Consensus statement: Using laryngeal electromyography for the diagnosis and treatment of vocal cord paralysis.

INTRODUCTION: The purpose of this study was to develop an evidence-based consensus statement regarding use of laryngeal electromyography (LEMG) for diagnosis and treatment of vocal fold paralysis after recurrent laryngeal neuropathy (RLN). METHODS: Two questions regarding LEMG were analyzed: (1) Does LEMG predict recovery in patients with acute unilateral or bilateral vocal fold paralysis? (2) Do LEMG findings change clinical management in these individuals? A systematic review was performed using American Academy of Neurology criteria for rating of diagnostic accuracy. RESULTS: Active voluntary motor unit potential recruitment and presence of polyphasic motor unit potentials within the first 6 months after lesion onset predicted recovery. Positive sharp waves and/or fibrillation potentials did not predict outcome. The presence of electrical synkinesis may decrease the likelihood of recovery, based on 1 published study. LEMG altered clinical management by changing the initial diagnosis from RLN in 48% of cases. Cricoarytenoid fixation and superior laryngeal neuropathy were the most common other diagnoses observed. CONCLUSIONS: If prognostic information is required in a patient with vocal fold paralysis that is more than 4 weeks and less than 6 months in duration, then LEMG should be performed. LEMG may be performed to clarify treatment decisions for vocal fold immobility that is presumed to be caused by RLN. Muscle Nerve 53: 850-855, 2016.

Genetics of upper and lower airway diseases in the horse.

Genetic predispositions for guttural pouch tympany, recurrent laryngeal neuropathy and recurrent airway obstruction (RAO) are well documented. There is also evidence that exercise-induced pulmonary haemorrhage and infectious diseases of the respiratory tract in horses have a genetic component. The clinical expression of equine respiratory diseases with a genetic basis results from complex interactions between the environment and the genetic make-up of each individual horse. The genetic effects are likely to be due to variations in several genes, i.e. they are polygenic. It is therefore unlikely that single gene tests will be diagnostically useful in these disorders. Genetic profiling panels, combining several genetic factors with an assessment of environmental risk factors, may have greater value, but much work is still needed to uncover diagnostically useful genetic markers or even causative variants for equine respiratory diseases. Nonetheless, chromosomal regions associated with guttural pouch tympany, recurrent laryngeal neuropathy and RAO have been identified. The association of RAO with other hypersensitivities and with resistance to intestinal parasites requires further study. This review aims to provide an overview of the available data and current thoughts on the genetics of equine airway diseases.

Intracisternal cranial root accessory nerve schwannoma associated with recurrent laryngeal neuropathy.

Intracisternal accessory nerve schwannomas are very rare; only 18 cases have been reported in the literature. In the majority of cases, the tumor origin was the spinal root of the accessory nerve and the tumors usually presented with symptoms and signs of intracranial hypertension, cerebellar ataxia, and myelopathy. Here, we report a unique case of an intracisternal schwannoma arising from the cranial root of the accessory nerve in a 58-year-old woman. The patient presented with the atypical symptom of hoarseness associated with recurrent laryngeal neuropathy which is noted by needle electromyography, and mild hypesthesia on the left side of her body. The tumor was completely removed with sacrifice of the originating nerve rootlet, but no additional neurological deficits. In this report, we describe the anatomical basis for the patient's unusual clinical symptoms and discuss the feasibility and safety of sacrificing the cranial rootlet of the accessory nerve in an effort to achieve total tumor resection. To our knowledge, this is the first case of schwannoma originating from the cranial root of the accessory nerve that has been associated with the symptoms of recurrent laryngeal neuropathy.

Ultrasound-guided biopsy of the cricoarytenoideus lateralis muscle: technique and safety in horses.

REASONS FOR PERFORMING STUDY: Current diagnosis of recurrent laryngeal neuropathy (RLN) depends upon disease recognition in the clinically affected horse. Biopsy of the intrinsic laryngeal muscles may provide a method to identify the changes in fibre-type composition that occur in RLN before clinical signs become apparent. OBJECTIVE: To develop an ultrasound-guided biopsy technique of the left cricoarytenoideus lateralis muscle (CALM) and evaluate its efficacy and safety in vivo. STUDY DESIGN: A longitudinal descriptive study. METHODS: Six standing horses underwent ultrasound-guided biopsy of the left CALM. Frozen muscle cores were obtained with a breast biopsy tool. Serial endoscopic, ultrasonographic and physical examinations before and for 8 weeks after the biopsy were assessed for iatrogenic trauma. Histologies of representative muscle core cross-sections were analysed for the total number of muscle fibres obtained with each biopsy. RESULTS: There were no immediate complications of the procedure and the left CALM was harvested in all instances. Biopsy samples had an average weight of 0.043 g (range = 0.023-0.077 g) and contained 3418 fibres in cross-section (range = 711-7143). Laryngeal endoscopic grade did not change significantly between prebiopsy and the end of the 8 week follow-up. The left CALM had significantly greater echogenicity than the right throughout the study (P<0.001), but there was no difference between the prebiopsy CALM echogenicity and that at completion of the study. CONCLUSIONS: Ultrasound-guided biopsy of the left CALM is safe and well tolerated, providing a minimally invasive method to obtain muscle from healthy horses. This new technique may be applicable in research and clinical settings.

Intracisternal Cranial Root Accessory Nerve Schwannoma Associated with Recurrent Laryngeal Neuropathy

Intracisternal accessory nerve schwannomas are very rare; only 18 cases have been reported in the literature. In the majority of cases, the tumor origin was the spinal root of the accessory nerve and the tumors usually presented with symptoms and signs of intracranial hypertension, cerebellar ataxia, and myelopathy. Here, we report a unique case of an intracisternal schwannoma arising from the cranial root of the accessory nerve in a 58-year-old woman. The patient presented with the atypical symptom of hoarseness associated with recurrent laryngeal neuropathy which is noted by needle electromyography, and mild hypesthesia on the left side of her body. The tumor was completely removed with sacrifice of the originating nerve rootlet, but no additional neurological deficits. In this report, we describe the anatomical basis for the patient's unusual clinical symptoms and discuss the feasibility and safety of sacrificing the cranial rootlet of the accessory nerve in an effort to achieve total tumor resection. To our knowledge, this is the first case of schwannoma originating from the cranial root of the accessory nerve that has been associated with the symptoms of recurrent laryngeal neuropathy.