Early detection and treatment of laryngeal neuropathy
John Cheetham, VetMB, Dipl. ACVS, Department of Clinical Sciences, Cornell University College of Veterinary Medicine, has recently received a grant from the Grayson-Jockey Club Research Foundation to study recurrent laryngeal neuropathy in horses.
Recurrent laryngeal neuropathy, also referred to as roaring, is a common disease in horses. Affected horses exhibit upper airway obstruction. It occurs, and is especially critical in, exercising horses since the nerves and muscles (cricoarytenoid dorsalis muscle) that control the movement of the arytenoid cartilages of the larynx do not function correctly, causing improper opening of the larynx during inspiration. This may lead to inadequate ventilation and poor performance during exercise.
The grant description notes: "Laryngeal neuropathy, or 'roaring,' is estimated by the author to affect 8 percent of race horses and a higher percentage of sport horses. This researcher over the last three years has developed two non-invasive procedures to assess the cricoarytenoid dorsalis (CAD) muscle and the nerve that supplies it. The CAD muscle is the only muscle that opens the larynx during exercise. The present proposal will validate two diagnostic tests for early detection of roaring in horses. The ability to identify young horses which are predisposed to become roarers would enable surgical intervention to restore the nerve supply before atrophy and fibrosis of the CAD muscle occurs.""What we're trying to do is work out which horses go on to develop laryngeal problems," says Cheetham. In most cases, recurrent laryngeal neuropathy is seen in racing horses at 2, 3 or 4 years of age with obstructed airway and poor performance. Tie-back, or laryngoplasty, which is the current form of surgical intervention, has a good success rate. "But there is room for improvement, and there are some possible complications associated with it," Cheetham says.
One of the recurrent laryngeal neuropathy research goals is to try to detect which horses will go on to develop the disease. Cheetham is investigating whether a diagnostic test could be applied to a weanling population that will tell us which horses are going to develop disease during their 2-, 3- or 4-year-old season.
The impact of the Grayson-Jockey Club Research Foundation grant will be twofold.
"First, we could intervene much earlier," says Cheetham. "So if we knew that there was a 90 percent chance that a particular horse was going to develop disease, then perhaps we could do a reinnervation technique or some other technique that would give us a better success rate."
Thus, it would mean that a horse would not experience time out of training or a break in its career and perhaps not be exposed to some of the complications of the tie-back procedure. "Although tie-back is a good procedure, and I certainly wouldn't discourage it, we're just trying to improve things all the time," says Cheetham.
"Second, it would also give trainers an idea of which horses to focus their efforts on and which young horses would perhaps be better doing a different job—possibly discontinuing training," says Cheetham.