Recurrent laryngeal neuropathy, often referred to by the colloquial term of “roaring,” is an inability of a horse to fully abduct (open) the arytenoid cartilages in the larynx, thereby resulting in a hollow whistle on inspiration during exercise. The development behind the roaring disease process is not fully under-stood, but is due to damage to the recur-rent laryngeal nerve which innervates the muscle responsible for opening the arytenoids. This nerve travels from the brain, down the neck to the chest and then turns, traveling back up the neck to the larynx. The left nerve is longer than the right and makes its turn around the aorta. Typical cases thought to have a hereditary component involve the left side only.
The nerves can also be damaged by trauma such as kicks or misplaced intravenous injections. If the right side is involved, which is very uncommon, trauma or injection issues will be the cause. Younger racehorses are commonly affected and are some-times diagnosed before they have started racing training. Up to 8% of racing thoroughbreds have been reported to be roarers to some degree, and the incidence for draft horses has been reported to be as high as 35%.
Diagnosis of a horse as a roarer is commonly suspected based on physical examination and a history of exercise intolerance. Definitive diagnosis is often made by endoscopic examination of the upper respiratory tract where visualization of the lack of abduction confirms this disease. Horses in the later stages of the disease process can be easily diagnosed withresting endoscopy; however, young race horses that intermittently exhibit signs when the condition is less advanced may require a dynamic endoscopy where the horse is exercised with a portable endoscope visualizing the back of the throat. This allows the veterinarian to determine if the airway remains open. Some veterinarians will also augment their physical exam by palpating the dorsal aspect of the larynx and slapping their hand on the horse’s withers in order to elicit a twitch of the cricoarytenoideus dorsalis muscle (the muscle responsible for opening the arytenoid cartilage); lack of a muscular twitch during the aptly-named “slap test” indicates a potential roarer. Because of the subjective nature of the degree to which the arytenoid cartilages abduct, a grading system has been implemented for veterinarians to more accurately describe the degree of arytenoid paralysis from grades I-IV with grade I horses being unaffected to grade IV horses having complete immobility and paralysis of the cartilage.
The standard treatment for roaring horses is a surgical procedure called a laryngoplasty, where a permanent suture is tied between the cricoid and arytenoid cartilages, giving the procedure its colloquial name “tie-back”. The goal of this operation is to use the suture to pull the arytenoid cartilage into a more open position, thereby increasing the size of the airway to allow better air flow and reduce the whistling noise. Care must be taken not to overly abduct the arytenoid cartilage so that saliva, food and water do not enter the windpipe; however, this condition can rarely occur even with nor-mal abduction. Other procedures commonly performed in conjunction with the tie-back are the ventriculectomy or the ventriculocordectomy which remove the ventricle and/or associated vocal cord in order to open the ventral portion of the larynx and potentially reduce the amount of respiratory noise even further.
Horses that undergo repair for laryngeal paralysis are typically kept in stalls for up to two months after surgery and owners are encouraged to feed them hay and grain on the ground in order to help reduce the chances of aspiration of food and water into the trachea. Light exercise is generally restarted anywhere between four to twelve weeks post-operatively. Horses generally have a good to return to performance, with 60-70% of racehorses and 80-90% of show horses returning to function.
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About the Author:
George L. Elane, DVM
The opportunity to be in surgery rooms was the draw for Dr. Elane in his choice to intern at Peterson and Smith. His ambition is to become an equine sur-geon, doing soft tissue and orthopedic cases due to his special interests in lameness, podiatry and sports medicine. He could be the next Dr. Donnie Slone!
Dr. Elane grew up in Laurel, Maryland and always knew his love for animals would make him a veterinarian. He went to Auburn University for his undergrad, earned his graduate’s degree from Vir-ginia Tech and after spending a three-week externship with Peterson and Smith, fell in love with Florida.
When he isn’t at the hospital, Dr. Elane enjoys reading, hiking, kayaking, camp-ing and hitting the driving range.
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