Description

Laryngeal hemiplegia is a common upper respiratory disorder in horses. It is characterized by paralysis in the horse's respiratory system involving one of the lyrangeal nerves, nearly always the left one. The vocal cord on that side becomes paralyzed and the affected flapper, which ordinarily opens and closes as the horse breathes in and out, is sucked into the airway when the horse inhales, obstructing the air flow.

A roaring or whistling sound occurs as the horse breathes in and the sounds are most evident as the horse begins to exercise..

Symptoms

• Characteristic roaring or whistling sound
• Exercise intolerance
• Unusual whinny
• Observation of reduced mobility of the arytenoid cartilage and vocal fold confirmed by endoscopy

Causes

Although very little is known about the cause of laryngeal hemiplegia, evidence shows that some cases are the result of a degenerative process affecting the laryngeal nerves. Heredity may be a factor in the development of the condition.

Laryngeal hemiplegia may also be caused by nerve damage related to traumatic injury, or other conditions and diseases, such as guttural pouch infections, strangles, tetanus, lead poisoning, and thrombophlebitis.

In cases of bilateral laryngeal paralysis when both vocal cords are affected, lead toxicity should be suspected. Although all breeds of horses are affected, male horses and longer-necked, larger breeds have the highest rate of this condition.

Prevention

Other than recommendations for using good horse management techniques to minimize injury or ingestion of toxic materials, little is available in horse literature about ways to prevent this condition. Early diagnosis is important to prevent debilitation due to exercise intolerance.

Treatment

Treatment usually involves some type of surgery and engaging the services of a knowledgeable veterinarian is crucial to maintaining the horse's well being. Once laryngeal hemiplegia is diagnosed through endoscopic examination and graded on a scale of one to four, the best method of treatment can be determined based on the use, age, and breed of the horse.

Prosthetic laryngoplasty can stabilize the affected side of the larynx and prevent collapse of the airway during exercise.

Laryngeal ventriculectomy may improve airflow and reduce the "roaring" sound during exercise. The lining of the ventricle and the vocal cord on the affected side are removed, often by using a laser technique.

A third way of treating the condition is with an arytenoidectomy. This method is usually reserved for horses that have had a failed laryngoplasty. Surgery removes the body of the arytenoid, leaving the muscular process intact. Complications include difficulty swallowing and pneumonia.

Another possible treatment is a neuromuscular graft. Young horses with grade three laryngeal hemiplegia are good candidates for this procedure. A nerve is isolated from one of the neck muscles, and a branch of that nerve is placed in the atrophied muscle. It usually takes from six to 12 months for the reinervation to occur, but reports show that 50% of horses improved their performance when this technique was used.

Complications often occur with any of these surgical procedures, and the services of an experienced veterinarian are important for the best possible outcome.