Early detection and treatment of laryngeal neuropathy - DVM
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Early detection and treatment of laryngeal neuropathy
A research grant investigating two diagnostic methods brings hope to affected horses


The research

Although he has recently received the Grayson-Jockey Club Research Foundation grant, Cheetham has been working on recurrent laryngeal neuropathy diagnosis and treatment options for a while. He started with laryngeal ultrasonography a few years ago, which involves looking at the lateral aspect of the larynx to evaluate one of the muscles (cricoarytenoideus lateralis) affected by laryngeal neuropathy. That procedure continues to be used at Cornell, Rood and Riddle Equine Hospital in Kentucky and Guelph University.

"During the last 12 months, we've developed a new technique, transesophageal ultrasound," says Cheetham. "We place a small esophageal probe about 15 mm in diameter up the nose and pass that into the esophagus, just over the top of the larynx. Using that, we can look down on the larynx itself and examine the two muscles that control the opening of the arytenoids—or flappers, as they are commonly called in the racing industry—the dorsal cricoarytenoid muscle," says Cheetham. "We can look at them directly and determine their geometry quite precisely, such as how thick they are, what the cross-section is and, to some degree, what the fiber pattern looks like within the muscle."

The other tool developed at Cornell is a way of directly measuring the speed of conduction of the nerve that innervates those muscles—the recurrent laryngeal nerve.

Using the Grayson-Jockey Club Research Foundation grant, over the next two years. Cheetham and colleagues at Cornell will look at these two techniques—nerve conduction velocity (measuring nerve health) and esophageal ultrasound (measuring the thickness of the two muscles responsible for opening the airway during exercise). They'll also investigate how these two techniques relate to exercising function. "This is the most important thing clinically," says Cheetham.

Once those data are determined, the next step will be to try to apply those to a population of young horses, probably weanlings. "That is probably a few years away," says Cheetham. "We are working on some new reinnervation techniques, so if we could pick up disease at an early stage, it would allow us to restore function using a nerve graft, a neuromuscular pedicle graft or some sort of nerve anastomosis. There are a whole slew of those techniques being developed."

The benefits

"With the two testing modalities Cheetham and colleagues will use—nerve conduction velocity and transesophageal ultrasound to look at dorsal cricoarytenoid muscle structure and anatomy—their goal is to determine nerve health and really try to relate those two diagnostic tests to the exercising arytenoid or laryngeal function," says Brett Woodie, DVM, MS, Dipl. ACVS, Rood and Riddle Equine Hospital.

"They're going to start out with adult horses and try to validate these techniques and then determine the sensitivity and specificity of those techniques as it relates to the diagnosis of recurrent laryngeal neuropathy," Woodie says. "With that in mind, they will then be able to take that information and use it in a younger group of horses to see if we can predict which horses will develop recurrent laryngeal neuropathy. And we'll have the capability to intervene at an earlier stage—to detect the disease early before they exhibit clinical signs of an abnormality."

Once Cheetham's research is completed, it is hoped that the new diagnosis and treatment methods will improve the plight of older horses on the racetrack, compared with current therapies.

"Everyone realizes that a laryngoplasty is not really a physiological solution to the problem as compared with the horse without a laryngoplasty," says Woodie. As also noted by Cheetham, laryngoplasty does have some complications associated with it. "But right now that is our best technique—along with some reinnervation procedures such as the neuromuscular pedicle graft—to deal with a horse that has laryngeal neuropathy," Woodie says.

The problem with the neuromuscular pedicle graft is that often the timeline, as far as the length of time it takes to determine if you've been successful or not, can affect a race horse's training schedule.

"A lot of the horses, because of their age, don't have the luxury of waiting an extra year before pursuing their racing career," Woodie says. "Being able to determine which horses will be affected at a later time may allow us to find other means to deal with this before we would need to use a laryngoplasty. I think that is really where it is headed—to stop the progression of the loss of those large myelinated nerve fibers before we get to the typical recurrent laryngeal neuropathy."


Source: DVM360 MAGAZINE,
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