My friend told me that my horse is a "roarer," but my vet says it has laryngeal hemiplegia. Please explain.

The term "roarer" may be used to describe a horse that has left recurrent laryngeal hemiplegia. Horses with left recurrent laryngeal hemiplegia often make loud breathing noises (described as "roaring" or "whistling") when they are exercising strenuously. In horses with left recurrent laryngeal hemiplegia, the left recurrent laryngeal nerve dies back and is no longer able to stimulate the muscle that enlarges the opening of the larynx (throat) during intense exercise to allow more air to be taken into the lungs. This muscle (the dorsal cricoarytenoid muscle) enlarges the diameter of the airways during exercise by pulling the arytenoid cartilage and vocal cord away from the midline of the larynx. Without stimulation from the left recurrent laryngeal nerve, the dorsal cricoarytenoid muscle becomes paralyzed. As a result, the arytenoid cartilage and vocal cord on the left side of the larynx collapse and are sucked into the airway during exercise. Air flowing over this obstruction is most likely responsible for the loud breathing noises called "roaring" in horses with left recurrent laryngeal hemiplegia.

Which horses are more likely to be affected with left recurrent laryngeal hemiplegia?
Left recurrent laryngeal hemiplegia is most often observed in horses between ages two and seven after they have begun training. The disease appears to be more common in large breed horses (greater than seventeen hands). There is some evidence that left recurrent laryngeal hemiplegia may be hereditary. Left recurrent laryngeal hemiplegia may also be associated with localized infections, certain toxins, or trauma to the left recurrent laryngeal nerve.

How is left recurrent laryngeal hemiplegia diagnosed?
Horses with left recurrent laryngeal hemiplegia may exhibit some degree of exercise intolerance and will make loud breathing noises described as "roaring" or "whistling" during strenuous exercise. The performance level of an afflicted horse may progressively decline over a period of weeks or months. Some horses may develop a cough or a change in their neigh.

Horses brought to a veterinarian after exhibiting these signs will receive a complete physical examination to rule out other causes of poor performance. When a horse has left recurrent laryngeal hemiplegia, the dorsal cricoarytenoid muscle atrophies (shrinks or wastes). The veterinarian may palpate the larynx to determine if the dorsal cricoarytenoid muscle has atrophied. If the dorsal cricoarytenoid muscle has become paralyzed due to lack of stimulation by the left recurrent laryngeal nerve, then the arytenoid cartilage and vocal cord on the affected side collapse into the larynx during inhalation and obstruct the airways. Endoscopic examination of the larynx during rest enables the veterinarian to see if the arytenoid cartilages are moving synchronously during breathing.

In normal horses, the arytenoid cartilages can be pulled out of the airway during breathing by the dorsal cricoarytenoid muscle. Some horses with left recurrent laryngeal hemiplegia can be endoscopically observed to have collapse of the arytenoid cartilage and vocal cord into the airway while at rest. Horses with clinical signs of laryngeal hemiplegia (such as loud breathing noises during exercise) that have no visible collapse of the arytenoid cartilage into the airway at rest should have their larynx examined by videoendoscopy while exercising strenuously on a treadmill. Horses that have never been on a treadmill will need to be trained to run on the treadmill over a period of several days before the videoendoscopic examination. If the arytenoid cartilage and vocal cord are observed to collapse into the airway during strenuous exercise on a high speed treadmill, then a diagnosis of left recurrent laryngeal hemiplegia is confirmed.

Is there any treatment for left recurrent laryngeal hemiplegia?
There are a number of different surgical treatments for left recurrent laryngeal hemiplegia. The preferred surgical procedure at this time is called prosthetic laryngoplasty ("tie-back"). In prosthetic laryngoplasty, a suture is used to replace the paralyzed dorsal cricoarytenoid muscle and permanently abduct the arytenoid cartilage to a normal resting position. This procedure also abducts the vocal cord. The suture prevents the arytenoid cartilage and vocal cord from collapsing into the airway during strenuous exercise.

Another surgical procedure that can be performed is called ventriculectomy. The laryngeal ventricles are outpouchings of mucosa bounded medially by the arytenoid cartilages and vocal cords. In a ventriculectomy, the ventricle mucosa is removed which causes the ventricle to collapse and the vocal cord to adhere to the wall of the larynx. This increases the diameter of the larynx and may abolish abnormal breathing noises but does not prevent the arytenoid cartilage from collapsing into the airway during strenuous exercise.

This article was prepared by Rachele J. Baker under the direction of the faculty and staff of the Equine Pulmonary Laboratory, College of Veterinary Medicine, Michigan State University. For a more detailed discussion (including illustrations and a video) on this subject, please see the article entitled Left Recurrent Laryngeal Hemiplegia at the Equine Pulmonary Laboratory at Michigan State University.

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