New Treatment Helps Horses Breathe Easier

Recurrent laryngeal neuropathy (RLN) is a common degenerative respiratory disease in horses that can sometimes lead to partial paralysis of the left half of the larynx. The current surgical methods to treat RLN often fail over time—sometimes even immediately after the procedure—which means a better treatment method is greatly needed.

Investigators from the University of Illinois College of Veterinary Medicine recently developed a new surgical technique to meet this need. Their research, funded by Morris Animal Foundation and published in the American Journal of Veterinary Research, hopes to improve outcomes after surgery for horses suffering from RLN.

Current Treatment Approaches

Owners of horses diagnosed with RLN have several treatment options to consider, each of which has benefits and drawbacks depending on the case:

• Prosthetic laryngoplasty (tie-back surgery): Places prosthetic sutures in the cricoid and arytenoid cartilage, keeping half of the larynx in an open position.
• Ventriculectomy (“Hobday”) and ventriculocordectomy: Removes a pocket of mucosal tissue of the larynx
• Nerve muscle pedicle graft technique: Grafts a piece of nerve and muscle onto the larynx.
• Partial arytenoidectomy: Widens the laryngeal opening connecting the pharynx and the larynx.
• Tracheostomy/tracheotomy: Places a permanent tube in the trachea.
• Retirement to a less athletic career: Racehorses are most commonly diagnosed with RLN.

The most popular of these treatments is tie-back surgery. During this procedure, veterinarians place prosthetic sutures in the cricoid and arytenoid cartilage, maintaining half of the larynx in an open position. While this sometimes restores normal airway function to the horse, the sutures usually do not hold for long in the soft cartilage tissue.

New Surgical Method

To solve this recurring problem, researchers developed what they call the toggle technique, in which nonabsorbable sutures are anchored to the arytenoid cartilage between 2 points with a stainless-steel button at one end.

“This is a truly impressive advancement to an existing technique in equine surgery,” said Kelly Diehl, DVM, DACVIM (SAIM), senior scientific programs and communications adviser at Morris Animal Foundation. “A stronger anchor point improves surgical outcomes, gives afflicted horses a higher quality of life, and may even save the lives of horses struggling with this disease.”

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The research team tested this new method against tie-back surgery with 41 equine cadaver larynges. One side of the laryngoplasty construct was created with the standard tie-back surgical method, and the other side was created with the new toggle surgical method. Then, the research team mimicked the forces a horse would create while swallowing or coughing.

The loss of arytenoid abduction for the 2 different sides was evaluated every 500 cycles. As a result, 11 of the 20 laryngoplasty constructs created by the tie-back technique failed or achieved Dixon grade 3 abduction, whereas 0 of the 20 laryngoplasty constructs created by the toggle technique failed. In other words, the toggle technique had a significantly greater survival rate of over 10,000 cycles.

“It’s a biomechanically superior technique to treat a limiting condition in horses that are supposed to perform,” said Santiago D. Gutierrez-Nibeyro, DVM, MS, clinical associate professor of equine surgery and the study’s lead investigator, “possibly saving them from having to be euthanized or given away by their owners.”

Besides the success with the equine cadavers, Dr. Gutierrez-Nibeyro said his team tried the new technique on a handful of live horses, also with positive results.

Conclusion

While RLN is not life-threatening for most horses, it greatly affects their ability to breathe properly during exercise, sometimes causing partial laryngeal paralysis. The cause of this degenerative disease remains unknown, but with better treatment methods, such as the toggle technique, affected horses can live longer, healthier lives.

“We were really pleased with our results,” Dr. Gutierrez-Nibeyro said, “and feel this is the way we’re going to be correcting RLN in the future.”