Laryngeal Hemiplegia (Roaring)


Left recurrent laryngeal hemiplegia is a disease of horses which makes breathing more difficult and therefore impairs performance. During exercise, horses with left recurrent laryngeal hemiplegia make loud breathing noises that are described as "roaring" or "whistling."

To get more air into their lungs during exercise, horses dilate their nostrils, nasopharynx, and larynx. Two nerves, the right recurrent laryngeal nerve and the left recurrent laryngeal nerve, cause muscle contraction, which leads to the dilation of the larynx to facilitate breathing during exercise. Laryngeal hemiplegia is caused by degeneration (paralysis) of typically the left recurrent laryngeal nerve. With the loss of the nerve, the muscle on the left side of the larynx wastes away and is no longer capable of dilating the larynx. With the right recurrent laryngeal nerve still functioning horses can still breath, but they fatigue more quickly as compared to normal horses.

The condition has been reported in horses as young as two months of age but is most commonly found in horses between ages two and seven that are beginning their performance careers.

There is a genetic tendency for the development of the condition with large, long-necked horses (Belgians, Thoroughbreds) being at highest risk. In these horses no reason has been found for the nerve degeneration, although some theories exist. Less commonly trauma, such as that sustained by a kick or a laceration, can injure the nerve and result in laryngeal hemiplegia.



Home Care

Horses recovering from surgery require four weeks of stall rest before they are permitted to exercise. During this period of rest the tissues surrounding the suture heal, providing further strength to the repair.

Prognosis for success is good, ranging from 50 to 90 percent, depending on the horse's occupation. Horses can be returned to their regular work by eight weeks following surgery.

Major complications include failure of the suture, infection, coughing, and aspiration of feed material while eating.

Preventative Care

As most cases develop without a predisposing cause, there is little in the way of prevention. Injections into the neck area (including veins) should only be administered by qualified personnel as reaction to a drug placed inappropriately can result in nerve injury.

When purchasing a horse for high level or racing competition, even if the horse is a yearling, an endoscopic examination of the larynx should be performed.

1) respiratory noise – soft whistle to "roar" as air moves past the collapsed arytenoid cartilage and vocal cord.

2) poor performance – exercise tolerance progressively declines as the function of the nerve and muscle progressively deteriorates. This may occur over several weeks to months.

3) impaired vocalization – affected horses may have an abnormal whinny, as their ability to tense the vocal cord is lost.

Grade I – Arytenoids are in normal resting position and when stimulated to open have simultaneous complete abduction.

Grade II – Arytenoids are in normal resting position but when stimulated to open the left responds more slowly than the right but will completely abduct.

Grade III – The left arytenoid is in a more closed position than normal, opens more slowly than the right side, and does not abduct fully.

Grade IV – The left arytenoid is in a closed (adducted) position and fails to show any movement when stimulated to abduct.