Recurrent laryngeal neuropathy (RLN), also referred to commonly as roarers or laryngeal hemiplegia, is a common performance limiting neurological condition which results in reduced airflow to the horse's lungs. It leads to progressive exercise intolerance and a characteristic respiratory noise that sounds similar to "roaring" when exercised. RLN is most frequently seen in Thoroughbred race horses and large Draft horse breeds. It is usually seen in taller (over 15 hands) male horses.
The exact cause of the condition is unknown, however proposed theories include genetics or environmental (due to injury or stretching or squashing of the recurrent laryngeal nerve (which supplies nerves to the larynx). This nerve progressively weakens until it is destroyed. Usually the left side of the larynx is affected (in 95% of cases), where it is partially to completely paralyzed.
Surgery is the only known treatment for horses with RLN. There are multiple surgical techniques used, with varying success rates and associated complications. Complications from these surgeries can result in poor performance themselves as they include aspiration pneumonia, lower airway diseases, and even euthanasia if the surgery is not successful.
The most common surgical procedure involving "tying back" the paralyzed cartilage so that it remains in an open position. It can be performed while the horse is under standing sedation or general anesthesia. The procedure is the most common treatment for horses with RLN and is usually effective for restoring free airflow, but there is a risk of recurrence if the sutures tear out or if the tissues are stretched during muscle movement around the larynx.
A surgical procedure involving the removal of the ventricle and vocal cord, to widen the airway and may be performed by itself or alongside a prosthetic laryngoplasty. There are two techniques involved---via an incision under the jaw or by using a laser passed through an endoscope up the horse's nostril. When the laser is used, the procedure can be performed while the horse is under standing sedation. When an incision is made in the jaw, then general anesthesia is necessary.
A surgical procedure involving the removal of the paralyzed arytenoid cartilage. It is usually the choice for horses with an infected arytenoid cartilage or who had previous had a tie-back surgery which was unsuccessful. The procedure requires general anesthesia and is done through an incision into the throat.
Neuromuscular Pedicle Graft
A surgical procedure that re-innervates the muscles that control abduction of the arytenoid cartilage. Horses which have previously received a tie-back procedure are unable to have this procedure due to loss of nerve function.
Prognosis depends on the horse’s required level of performance and surgical treatment performed. Overall success rates ranges from 50-90%; racehorses and those with a higher demand for airflow have slightly lower success rates while show horses, draft horses, and pleasure horses tend to have higher