Nervus laryngeus recurrens
The recurrent laryngeal nerve is a branch of the vagus nerve (cranial nerve X) with immense clinical significance in equine medicine. 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 approximately 2-meter journey makes it the longest peripheral nerve course relative to cell body distance in the horse. It provides motor innervation to all intrinsic laryngeal muscles except the cricothyroid (which is innervated by the cranial laryngeal nerve).
The recurrent laryngeal nerve is a branch of the vagus nerve (CN X). The left nerve has a uniquely long course: it descends into the thorax, loops around the aortic arch, and ascends back to the larynx; a total distance of approximately 2 meters. This length predisposes it to distal axonopathy. Diagnosis requires endoscopy (resting and dynamic/overground). Surgical options include prosthetic laryngoplasty (tie-back) ± ventriculocordectomy. RLN affects up to 3-8% of Thoroughbreds and is even more common in draft breeds.
Recurrent laryngeal neuropathy (RLN), commonly known as roaring or whistling, is a progressive degeneration of the left recurrent laryngeal nerve leading to paralysis of the left arytenoid cartilage.
Paralysis of both arytenoid cartilages due to bilateral recurrent laryngeal nerve damage. Much rarer than unilateral RLN. May occur with organophosphate toxicity, lead poisoning, guttural pouch mycosi
Congenital malformation affecting structures derived from the fourth branchial arch, including the cricothyroid muscle (innervated by the cranial laryngeal nerve) and potentially affecting arytenoid f
Recurrent laryngeal neuropathy (RLN), commonly known as roaring or whistling, is a progressive degeneration of the left recurrent laryngeal nerve leading to paralysis 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. The condition is graded I to IV on endoscopic examination (Havemeyer system), with higher grades causing more significant airway obstruction. ## 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. The left side is affected in over 95% of cases due to the longer nerve pathway. ## 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. Mild cases (Grade I to II) 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. Early detection through routine endoscopic screening in young performance horses can allow for timely intervention. ## 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
Paralysis of both arytenoid cartilages due to bilateral recurrent laryngeal nerve damage. Much rarer than unilateral RLN. May occur with organophosphate toxicity, lead poisoning, guttural pouch mycosis, or hepatoencephalopathy. Signs include: Severe inspiratory dyspnea at rest and exercise; stridor; complete upper airway obstruction may occur; emergency tracheostomy may be needed
Congenital malformation affecting structures derived from the fourth branchial arch, including the cricothyroid muscle (innervated by the cranial laryngeal nerve) and potentially affecting arytenoid function. Signs include: Dysphagia; abnormal respiratory noise from birth; arytenoid collapse; rostral displacement of the palatopharyngeal arch (RDPA)
The recurrent laryngeal nerve is a branch of the vagus nerve (CN X). The left nerve has a uniquely long course: it descends into the thorax, loops around the aortic arch, and ascends back to the larynx; a total distance of approximately 2 meters. This length predisposes it to distal axonopathy. Diagnosis requires endoscopy (resting and dynamic/overground). Surgical options include prosthetic laryngoplasty (tie-back) ± ventriculocordectomy. RLN affects up to 3-8% of Thoroughbreds and is even more common in draft breeds.
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