Laryngeal Hemiplegia (Roaring)
Dr. Patricia Provost
A presumptive diagnosis of laryngeal hemiplegia can be made based on the performance history of the horse and the classic noise that they make while breathing during exercise. Affected horses may also have an abnormal whinny, because the loss of the nerve also affects the vocal cord on the same side.
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.
To make a definitive diagnosis, your veterinarian will use a fiberoptic scope to view the larynx as it opens and closes during breathing.
Treatment is only required when the condition adversely affects the athletic performance of the horse. Most horses have sufficient breathing capacity to take in enough oxygen to perform at rather rigorous levels of work. High-speed distance horses (racehorses, advanced three day event horses, grand prix level jumpers) are typically the only ones in which oxygen intake is affected. To eliminate the abnormal respiratory noise, the "roar," represents the reason why most other show ring horses are treated.
A prosthetic laryngoplasty surgical procedure, known as a tieback surgery, is the most common method used to treat the condition. A permanent suture is placed surgically to mimic the action of the atrophied muscle and keep the larynx dilated on the affected side. There are no medical treatments.
To decrease the abnormal respiratory noise, removal of the vocal cord on the affected side is often done in combination with the tieback procedure.
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.
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.