Nervus laryngeus recurrens
The recurrent laryngeal nerve is a branch of the vagus nerve (cranial nerve X). It provides motor innervation to all intrinsic laryngeal muscles except the cricothyroid (which is innervated by the cranial laryngeal nerve). The left recurrent laryngeal nerve has an extraordinarily long course: it branches from the vagus in the thorax, loops caudally around the aortic arch (ligamentum arteriosum), then ascends the entire length of the neck back to the larynx. This long journey (approximately 2 meters relative to cell-body distance) makes it vulnerable to degeneration. The right nerve has a shorter course. Dysfunction of the left recurrent laryngeal nerve leads to paralysis of the left cricoarytenoideus dorsalis muscle and inability to abduct the left arytenoid cartilage during exercise.
Left laryngeal hemiplegia (roaring) is a common cause of abnormal inspiratory noise and exercise intolerance, especially in large breed horses. Diagnosis uses resting and dynamic endoscopy. Treatment options include prosthetic laryngoplasty (tie-back) and other surgical procedures. The long course of the left nerve is the primary reason the left side is almost always affected.
Recurrent laryngeal neuropathy (RLN), commonly known as roaring or whistling, is a progressive degeneration of the recurrent laryngeal nerves, mainly affecting the left side and reducing or preventing
## Overview Bilateral laryngeal paralysis is the uncommon loss of function of both arytenoid cartilages, so that neither can abduct (open) properly during inspiration. Unlike the far more common left
## Overview 4-BAD is the acronym for fourth branchial arch defect, a congenital laryngeal dysplasia. Characteristic endoscopic findings include reduced arytenoid movement and rostral displacement of
Inspiratory noise during exercise (especially a roaring or whistling sound) and poor performance should be evaluated. Dynamic endoscopy is often required for accurate diagnosis.
Recurrent laryngeal neuropathy (RLN), commonly known as roaring or whistling, is a progressive degeneration of the recurrent laryngeal nerves, mainly affecting the left side and reducing or preventing movement of the left arytenoid cartilage. This results in reduced airway diameter during inspiration and the characteristic inspiratory noise during exercise. It is one of the most important upper airway conditions affecting performance horses. ## What it is The left recurrent laryngeal nerve has a very long course (wrapping around the aortic arch), making it more susceptible to damage than the right nerve. Progressive axonopathy leads to denervation and atrophy of the cricoarytenoideus dorsalis (CAD) muscle, the only abductor of the arytenoid cartilage. As a result, the left arytenoid fails to open fully during exercise, causing turbulent airflow and the classic roaring sound. Laryngeal function is graded I to IV on resting endoscopic examination (Havemeyer system), with higher grades indicating greater impairment of arytenoid movement. ## Signs and symptoms - Inspiratory noise ('roaring' or 'whistling') during exercise that worsens with speed and fatigue - Exercise intolerance or reduced performance - In severe cases, respiratory distress during intense work - Abnormal arytenoid movement on resting or exercising endoscopy - The noise is often absent or minimal at rest and becomes obvious only during exercise ## Causes and risk factors RLN is a distal axonopathy whose exact cause is not fully understood but has a genetic component. It is more common in larger horses (especially Thoroughbreds and drafts) and appears to have a hereditary predisposition. Risk increases with age and size. Clinical disease is predominantly left-sided; the longer left nerve is thought to contribute. ## How it is diagnosed Diagnosis is confirmed by endoscopic examination of the larynx, ideally during exercise (dynamic endoscopy) to assess arytenoid function under stress. Resting endoscopy can grade the degree of paralysis but may underestimate the severity. The Havemeyer grading system (I to IV) is used to classify the severity based on arytenoid movement and position. ## Treatment and management Treatment depends on the grade and the horse's intended use. Horses with Grade I to II laryngeal function may not require intervention. For performance horses with Grade III or IV, surgical options include laryngoplasty (tie-back procedure), in which the arytenoid is permanently fixed in an open position, often combined with ventriculocordectomy (removal of the vocal cord and ventricle). Other procedures such as arytenoidectomy are used in selected cases. Post-operative care and rehabilitation are important for success. ## When to call the vet Contact your veterinarian if your horse develops an abnormal respiratory noise during exercise or shows signs of reduced performance. Dynamic endoscopy is the best way to confirm the diagnosis and determine the appropriate treatment. ## Prevention There is no proven way to prevent RLN, but selective breeding away from affected lines may help reduce incidence over time. Endoscopic assessment of laryngeal function can help guide decisions about whether intervention is needed. ## Frequently asked questions **Can a horse with roaring still compete?** Many horses return to successful competition after laryngoplasty (tie-back), though some degree of noise may remain and results vary. **Is roaring painful?** No. RLN itself is not painful, but the reduced airway can limit performance and, in severe cases, cause respiratory distress. **Does the tie-back surgery last forever?** The surgery provides long-term improvement in most horses, but complications such as implant failure or aspiration can occur in some cases. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Inspiratory noise ('roaring' or 'whistling') during exercise that worsens with speed and fatigue; exercise intolerance or reduced performance; in severe cases, respiratory distress during intense work; abnormal arytenoid movement on resting or exercising endoscopy; noise often absent at rest and becomes obvious only during exercise
## Overview Bilateral laryngeal paralysis is the uncommon loss of function of both arytenoid cartilages, so that neither can abduct (open) properly during inspiration. Unlike the far more common left-sided recurrent laryngeal neuropathy (“roaring”), bilateral disease produces severe airway obstruction that can be life-threatening at rest. Causes include lead toxicity, certain plant poisonings, trauma, post-anesthetic neuropathy, and occasional neurologic diseases. ## Causes Lead poisoning is a classic cause and should always be considered. Other toxins, bilateral recurrent laryngeal nerve trauma, post-anesthetic complications, and central or peripheral neuropathies (for example equine protozoal myeloencephalitis) can also produce bilateral paralysis. The evidence for exact frequency of each cause is limited. ## Diagnosis Endoscopy shows both arytenoids fixed in a paramedian or midline position with little or no movement. Horses present with severe inspiratory stridor and distress. Blood lead levels, neurologic examination, and additional imaging help identify the underlying cause. ## Treatment Emergency tracheostomy is often required to bypass the obstruction. Treatment of the primary disease (for example chelation for lead) is essential. Permanent tracheostomy or, in selected cases, arytenoidectomy may be needed for long-term management. Unilateral recovery sometimes occurs. ## Recovery and Prognosis Prognosis depends on the cause. Some toxic or post-anesthetic cases improve over weeks to months. Permanent bilateral paralysis usually requires lifelong airway management and limits athletic use. ## Prevention Avoidance of lead sources and careful anesthetic recovery reduce some risks. No specific prevention exists for idiopathic cases. Signs include: severe inspiratory noise; respiratory distress at rest; both arytenoids immobile on endoscopy; anxiety or collapse in advanced cases
## Overview 4-BAD is the acronym for fourth branchial arch defect, a congenital laryngeal dysplasia. Characteristic endoscopic findings include reduced arytenoid movement and rostral displacement of the palatopharyngeal arch. Clinical signs range from mild noise to dysphagia and exercise intolerance. ## Causes Embryologic malformation of fourth (and sometimes sixth) branchial arch derivatives. ## Diagnosis Endoscopy and advanced imaging of the larynx. ## Treatment Individualized. Some cases are monitored; others undergo surgical procedures aimed at improving airway function. ## Recovery and Prognosis Depends on the extent of the malformation. ## Prevention None. Signs include: dysphagia; abnormal respiratory noise from birth; arytenoid collapse; rostral displacement of the palatopharyngeal arch
Left laryngeal hemiplegia (roaring) is a common cause of abnormal inspiratory noise and exercise intolerance, especially in large breed horses. Diagnosis uses resting and dynamic endoscopy. Treatment options include prosthetic laryngoplasty (tie-back) and other surgical procedures. The long course of the left nerve is the primary reason the left side is almost always affected.
Inspiratory noise during exercise (especially a roaring or whistling sound) and poor performance should be evaluated. Dynamic endoscopy is often required for accurate diagnosis.
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