Proceedings of a Workshop on - The Havemeyer Foundation

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Havemeyer Foundation Monograph Series No. 11 Guidelines for endoscopic examination for the purpose <strong>of</strong> laryngeal evaluation 1. Evaluation should be performed with as little restraint as needed for safety <strong>of</strong> horse and personnel. 2. The use <strong>of</strong> chemical restraint can alter laryngeal function. 3. To achieve consistency in the endoscopic appearance <strong>of</strong> the larynx, it is recommended that the same nostril be used routinely for introduction <strong>of</strong> the endoscope. 4. The initial endoscopic examination should be conducted before rather than after exercise. This allows observation <strong>of</strong> a wider range <strong>of</strong> laryngeal movements. 5. During the endoscopic examination, laryngeal function should be observed during quiet breathing, swallowing and nasal occlusion. Clinical grading <strong>of</strong> RLN 1. Although a number <strong>of</strong> grading systems are available and validated, they consistently agree on the following: a) Inability to achieve full abduction <strong>of</strong> the affected arytenoid cartilage during examination is likely to be associated with compromised respiratory function during exercise. b) Glottic asymmetry at end-exhalation and asynchronous arytenoid movement during inhalation are not cause for concern as long as such horses can attain and maintain full bilateral abduction <strong>of</strong> their arytenoid cartilages. 2. The grading systems shown in Tables 2 and 3 is recommend by participants in the workshop. 3. There was no consensus on the functional significance <strong>of</strong> obtaining full arytenoid abduction that is not maintained symmetrically. 4. In the majority <strong>of</strong> horses, laryngeal function remains constant over time, but in some horses, laryngeal function can deteriorate over a few weeks to years regardless <strong>of</strong> initial endoscopic appearance. 5. Endoscopic evaluation <strong>of</strong> the larynx in weanlings for presence <strong>of</strong> RLN is an unreliable predictor <strong>of</strong> their laryngeal endoscopic appearance as yearlings. Other diagnostic procedures 1. Other tests <strong>of</strong> recurrent laryngeal function include palpatory and endoscopic assessment <strong>of</strong> the thoraco-laryngeal reflex (‘slap test’) and measurement <strong>of</strong> nerve conduction velocity, ie electrolaryngeogram. Currently, none <strong>of</strong> these procedures is believed to be as effective as endoscopic examination for diagnosing RLN. TREATMENT OF CLINICAL SIGNS ASSOCIATED WITH RLN 1. Surgical treatments used for relief <strong>of</strong> the clinical signs <strong>of</strong> RLN include ventriculectomy with or without vocalcordectomy, prosthetic laryngoplasty, various degrees <strong>of</strong> arytenoidectomy, and nerve muscle pedicle grafts (reinnervation surgery). 2. These procedures vary in their efficacy in the reduction <strong>of</strong> abnormal exercise related sounds and the relief <strong>of</strong> airway obstruction. 3. Most <strong>of</strong> the following conclusions are based on studies in experimentally induced laryngeal hemiplegia. In the following section ‘RLN’ signifies the naturally occurring condition. Abnormal upper respiratory sounds 1. Prosthetic laryngoplasty alone significantly reduces the abnormal upper airway noise in RLN afflicted horses. 2. Following prosthetic laryngoplasty, there is no clear correlation between the degree <strong>of</strong> residual upper respiratory noise and the magnitude <strong>of</strong> surgical arytenoid abduction. 3. The degree <strong>of</strong> noise reduction after laryngoplasty may be more a factor <strong>of</strong> stability <strong>of</strong> the arytenoid cartilage rather than the degree <strong>of</strong> arytenoid abduction. 4. Bilateral ventriculo-cordectomy can reduce abnormal upper airway sounds in horses with experimentally induced left laryngeal hemiplegia. 5. Unilateral ventriculo-cordectomy can reduce abnormal upper airway sounds in RLN afflicted horses. 95
Equine Recurrent Laryngeal Neuropathy TABLE 2: Grading system <strong>of</strong> laryngeal function performed in the standing unsedated horse † Grade Description Sub-grade I All arytenoid cartilage movements are synchronous and symmetrical and full arytenoid cartilage abduction can be achieved and maintained II Arytenoid cartilage movements are .1 Transient asynchrony, flutter or delayed asynchronous and/or larynx asymmetric movements are seen at times but full arytenoid cartilage .2 There is asymmetry <strong>of</strong> the rima glottidis abduction can be achieved and maintained much <strong>of</strong> the time due to reduced mobility <strong>of</strong> the affected arytenoid and vocal fold but there are occasions, typically after swallowing or nasal occlusion when full symmetrical abduction is achieved and maintained III Arytenoid cartilage movements are .1 There is asymmetry <strong>of</strong> the rima glottidis asynchronous and/or asymmetric. much <strong>of</strong> the time due to reduced mobility <strong>of</strong> Full arytenoid cartilage abduction the arytenoid and vocal fold but there are cannot be achieved and occasions, typically after swallowing or nasal maintained occlusion when full symmetrical abduction is achieved but not maintained .2 Obvious arytenoid abductor deficit and arytenoid asymmetry. Full abduction is never achieved .3 Marked but not total arytenoid abductor deficit and asymmetry with little arytenoid movement. Full abduction is never achieved IV Complete immobility <strong>of</strong> the arytenoid cartilage and vocal fold † Description generally refers to the left arytenoid cartilage in reference to the right. However this grading system can apply to the right side (ie right Grade III-1) 6. Following ventriculo-cordectomy abnormal upper airway sounds can continue to decrease for up to 90 days after surgery. 7. Bilateral ventriculo-cordectomy is superior to laryngoplasty alone in reduction <strong>of</strong> abnormal sounds in horses with experimentally induced left laryngeal hemiplegia. Exercise intolerance 1. Unilateral ventriculectomy is ineffective in restoring normal airflow in horses with experimentally induced left laryngeal hemiplegia. 2. Prosthetic laryngoplasty can restore normal airflow in horses with experimentally induced left laryngeal hemiplegia. 3. Prosthetic laryngoplasty combined with bilateral ventriculectomy can restore normal airflow in sport horses with RLN. 4. In most horses subjected to prosthetic laryngoplasty, the degree <strong>of</strong> abduction <strong>of</strong> the arytenoid cartilage will decrease by varying degrees in the post operative period. 5. Evidence from studies <strong>of</strong> sport horses with RLN and horses with experimentally induced laryngeal hemiplegia indicates that the post operative degrees <strong>of</strong> residual airway obstruction and the degree <strong>of</strong> abduction <strong>of</strong> the arytenoid cartilage are poorly correlated. 6. Maximal abduction <strong>of</strong> the arytenoid cartilage during prosthetic laryngoplasty may be unnecessary to restore laryngeal airway function and is probably undesirable by causing increased risk <strong>of</strong> aspiration and coughing. 7. Subtotal arytenoidectomy combined with ipsilateral ventriculectomy is ineffective in restoring airflow in horses with experimentally induced left laryngeal hemiplegia. 96
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Proceedings of a Workshop on - The Havemeyer Foundation

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