Bit & Bridle

Equine Laryngeal Hemiplegia (Roaring)

Other Names

  • Roaring
  • Recurrent Laryngeal Neuropathy (RLN)
  • Left Laryngeal Hemiplegia
  • Idiopathic Laryngeal Hemiplegia (ILH)

What is Equine Laryngeal Hemiplegia?

Equine laryngeal hemiplegia, widely known as “roaring,” is a condition in which one or both of the arytenoid cartilages of the larynx fail to abduct (open) fully during inspiration, reducing the diameter of the upper airway. In the vast majority of cases, it is the left side that is affected — hence the common term Left Laryngeal Hemiplegia.

The condition arises from progressive degeneration of the recurrent laryngeal nerve, which supplies the muscles responsible for opening the arytenoid cartilage. As the nerve degenerates, the cricoarytenoideus dorsalis (CAD) muscle — the primary abductor of the arytenoid — atrophies and loses function. During exercise, when inspiratory demand increases dramatically, the flaccid left arytenoid is sucked medially into the airway, obstructing airflow and producing the characteristic harsh, roaring or whistling sound during inhalation.

Laryngeal hemiplegia is most commonly diagnosed in large, tall horses — Thoroughbreds, Warmbloods, and Draught horses are disproportionately affected. It significantly limits the affected horse’s ability to work at high intensity, making it a major concern in racehorses and high-level performance horses. Learn more about upper airway anatomy in our larynx terminology guide.

Causes

  • Idiopathic recurrent laryngeal neuropathy: By far the most common cause. The exact trigger for the neuropathy is unknown, but it is associated with the length of the left recurrent laryngeal nerve — which, in large horses, must travel from the brain all the way to the thorax before looping back up to the larynx. The greater the length, the more vulnerable it is to demyelination and axonal loss.
  • Genetic predisposition: There is good evidence for a heritable component, with tall horses and certain bloodlines at increased risk
  • External trauma: Perivascular injections in the jugular groove, physical trauma to the neck, or surgery involving the vagosympathetic trunk can damage the recurrent laryngeal nerve
  • Guttural pouch disease: Mycosis or empyema of the guttural pouches can directly compress or damage the recurrent laryngeal nerve as it passes through or near this structure
  • Inflammatory conditions: Lymph node enlargement, neoplasia, or other space-occupying lesions in the neck region can cause nerve compression
  • Lead poisoning: A recognised but uncommon cause of peripheral neuropathy including laryngeal hemiplegia

Symptoms and Signs

  • Respiratory noise during exercise: A characteristic harsh, inspiratory roaring or whistling sound heard at canter or gallop. In milder cases the noise may only be audible at fast work.
  • Exercise intolerance: The horse fatigues early, slows, or becomes difficult to ride forward in fast work due to restricted airflow
  • Reduced performance: Often the first sign noticed — the horse simply does not perform to its expected level
  • Respiratory distress after exercise: Extended recovery time, laboured breathing, or prolonged blowing after fast work
  • No clinical signs at rest: Mild to moderate cases are typically silent and comfortable when not exercising

Diagnosis

Definitive diagnosis requires endoscopic examination of the larynx:

  • Standing endoscopy: Resting laryngoscopy via a flexible endoscope passed through the nostril allows direct visualisation of arytenoid movement. A standardised grading system (Havemeyer Grading Scale, grades 1–4) is used to quantify the degree of left arytenoid dysfunction — grade 4 represents complete paralysis.
  • Dynamic endoscopy (exercising): Because resting endoscopy can underestimate the degree of airway collapse, exercising endoscopy — conducted with a treadmill or an overground endoscope worn during ridden exercise — is considered the gold standard for accurate assessment, particularly for borderline cases.
  • Laryngeal palpation: Atrophy of the CAD muscle can sometimes be appreciated by palpation of the larynx, and tapping the larynx may fail to elicit the normal reflex adduction (the “slap test”), though this is not highly sensitive.
  • Upper airway radiography and ultrasound: Useful for identifying secondary causes such as guttural pouch disease or neck masses.

Treatment

Treatment aims to restore adequate airway diameter during exercise. Several options are available, with surgical intervention being the definitive treatment for moderate to severe cases:

  • Laryngoplasty (Tie-back surgery): The most widely performed procedure. A suture is placed to abduct and fix the affected arytenoid in an open position, permanently enlarging the airway. Results are best in horses with unilateral paralysis. Success rates for return to athletic function vary — around 50–70% of racehorses improve significantly, though some experience aspiration complications due to the permanently open larynx.
  • Ventriculectomy/ventriculocordectomy: Removal of the lateral ventricle and vocal cord on the affected side reduces the flapping tissue and is often performed in conjunction with laryngoplasty to improve airflow and reduce noise.
  • Laryngeal reinnervation: An emerging surgical technique in which a nerve-muscle pedicle graft is used to reinnervate the CAD muscle. Results in progressive improvement in arytenoid function over 6–12 months and avoids the aspiration risk of laryngoplasty. Currently available at specialist referral centres.
  • Conservative management: Horses with mild (grade 2) dysfunction and no significant exercise intolerance may be managed with modified work levels, avoiding fast or sustained uphill work, and addressing any contributing upper respiratory disease.

Prevention

There is no proven method to prevent idiopathic recurrent laryngeal neuropathy. However, the following reduce risk of secondary causes:

  • Perform all jugular vein injections carefully, avoiding perivascular injection
  • Investigate and treat guttural pouch disease promptly
  • Screen breeding stallions with significant laryngeal hemiplegia — evidence suggests heritability

Prognosis

For horses with mild dysfunction (grade 2) that are managed appropriately, prognosis for continued work at lower to moderate intensity is good. For horses in fast work with grade 3–4 dysfunction, surgical intervention offers the best chance of return to athletic performance. Post-laryngoplasty, approximately 50–70% of Thoroughbred racehorses return to racing. Horses in disciplines with lower aerobic demand (dressage, pleasure riding) generally tolerate the condition better than racehorses.

When to Call the Vet

  • Any horse making an abnormal respiratory noise during exercise — even if performance appears unaffected
  • Exercise intolerance of unexplained origin, particularly in large breeds
  • A horse that has been diagnosed with laryngeal hemiplegia and is deteriorating despite management
  • Any horse with suspected guttural pouch disease — this requires prompt investigation to protect the recurrent laryngeal nerve

Frequently Asked Questions

Will a horse that “roars” always need surgery?

Not necessarily. Mild grades of laryngeal dysfunction (grade 1–2) may not significantly affect a horse’s ability to work at moderate intensity, and many horses in lower-demand disciplines perform well without intervention. Surgery is generally recommended for horses in fast work, where the restricted airway causes meaningful exercise intolerance.

Why is it almost always the left side affected?

The left recurrent laryngeal nerve travels a significantly longer path than the right — it loops around the aorta in the thorax before ascending back to the larynx. This greater length makes it more susceptible to the stretch-related neuropathy that underlies the condition, particularly in tall horses where the nerve is longest. See BEVA resources for further reading on equine upper airway disease.

Can a horse breed if it has laryngeal hemiplegia?

From a physical standpoint, yes. However, given the heritable component of the condition, many breed registries and performance horse breeders take it into consideration. Horses with significant laryngeal hemiplegia are generally considered poor breeding prospects for performance breeds, as there is a reasonable chance of passing the predisposition to offspring.

Is the noise itself harmful to the horse?

The sound itself is not the problem — it is simply an indicator of airway turbulence. The harm lies in the restricted airflow, which limits oxygen delivery during exercise, causes the horse to fatigue earlier than it should, and in severe cases can cause significant respiratory distress. Horses with untreated significant hemiplegia may also inhale food and water (aspiration) due to incomplete glottic closure, which can lead to aspiration pneumonia.