The Harry M. Zweig Memorial Fund for Equine Research

Laryngeal Hemiplegia: Do We Have the Wrong Treatment?

Dr. Normand G. Ducharme and Dr. J. Brett Woodie

The voice box (larynx) consists of two flappers (arytenoid cartilages) that open when the horse needs air and closes when swallowing to protect the windpipe (trachea). Laryngeal hemiplegia (roaring) is a disease where one-half of the larynx becomes paralyzed. When one side is paralyzed, the affected flapper is sucked into the airway when the horse inhales, thus obstructing airflow. Laryngeal hemiplegia has been diagnosed for many centuries and affects 5-8% of Thoroughbred racehorses. This disease is very important to the equine industry because of its high incidence and its disastrous effect on the performance of the affected horse. There are two main surgical treatments for this disease. The current preferred treatment recommendation is a surgical procedure called a "tie-back" (laryngoplasty). This surgical procedure consists of stitching the paralyzed flapper in an open position so that normal airflow can be restored. The second procedure involves removing the flapper, (partial arytenoidectomy) such that it no longer obstructs the airway. The current belief is that the tieback procedure is the best procedure for treating roaring because it opens the airway the most and has fewer complications, such as coughing and aspiration of feed material and water into the trachea. This belief is based on experimental data indicating that in research horses, the airway is restored to normal after the tie-back procedure so that all treated horses should return to normal. In contrast, research horses that have had the flapper removed have shown their airway is improved, but not returned to normal.

We believe that the recommendation by throat surgeons worldwide to perform a tie-back surgery over flapper removal is not appropriate because of the following observations. First, despite the fact that in research horses a normal airway has been seen following tie-back surgery, in clinical patients only 60% (range50-60%) return to racing. In fact, a recent publication on the results of tie-back surgery, (December 2000) concluded that owners should be warned of the complications of tie-back surgery and that a guarded prognosis should be given. Second, Thoroughbred racehorse trainers have complained that of the 60% of horses that return to racing very rarely is their level of performance matching the trainer's expectations; i.e., although the horses may race, it performs at a lower level than expected. Third, our racetrack experience suggests that most horses can race after removing the flapper per our modified surgical technique. (We have added a modification to the technique that prevents/minimizes collapse of the soft tissue, a complication seen in horses treated for roaring by either a tie-back or partial arytenoidectomy). Indeed, after reviewing our results of horses treated with removal of the flapper, we noted that the success rate and owner satisfaction was higher after removal of the flapper than after a tie-back. After flapper removal in 17 racehorses from January 1997 to December 2001 at Cornell University Hospital for Animals, 1617 (94%) raced postoperatively. We compared this group of horses with racehorses that had a tie-back performed during the same time period and found that 1217 (71 %) raced postoperatively. Fourth, we have observed that horses after flapper removal exhibit much less coughing and feed aspiration than after the tie-back procedure. Finally, no studies have compared the two procedures in the same horse to assess their effects on size of the airway, complication rate, noise reduction, and degree of feed contamination of the windpipe (trachea).

One may question why the difference between the experimental data and the clinical situation? First, research horses are not involved in competition and no performance expectation is present. Although the research data suggests that the airway is normal following a tieback, veterinarians who examine the airway endoscopically post-surgery know this is not the case. Following surgery, the diameter of the airway is smaller than in a normal horse during exercise. In other words, airway mechanics tests are not sensitive enough (which is why in this proposed study we have added a direct measurement of blood oxygen content) to detect the abnormality. Third, in clinical patients, it is well established that the diameter of the opening of the voice box decreases over time (the suture or cartilage relaxes) after a tie-back. This decrease in size of the airway with time further decreases the amount of oxygen the horse can take in. Research horses are not normally kept long after surgery to evaluate this aspect.

Why are racehorses in our experience racing at a higher rate after flapper removal? First, removal of the flapper does not weaken with time so the airway size is maintained after surgery (i.e. there are no sutures to fail or cartilage to break) so the results are more consistent. Second, we believe that our modification of the flapper removal surgery has further increased the size of the airway after surgery such that it is no longer inferior to the results obtained soon after tie-back surgery. Third, we believe there is less tracheal contamination during eating and drinking thus preventing a decrease in performance associated with tracheitis or respiratory infection.

For these reasons, we question the usual dogma and suspect that the tie-back is an inferior technique compared to removal of the flapper; instead, we feel that removing the flapper is a better technique. Removal of the flapper is currently recommended only to treat infection of the flapper (arytenoid chondritis) or when the tieback has failed.

Both the tie-back and flapper removal interfere with the normal protective mechanisms of the larynx. Therefore, coughing and contamination of the trachea by feed material may be problematic and even lead to respiratory infection. We feel that in both procedures, the degree of windpipe contamination after surgery can be reduced by a simple management procedure of feeding and watering from the ground. This has never been evaluated in previous research studies.

We propose that this project, by supplying scientific data, could positively improve the success rate of racehorses affected with laryngeal hemiplegia from 60% to 80-90% simply by changing the recommended surgical treatment to a modified flapper removal technique. We hypothesize that modified flapper removal will improve airflow to a similar level as initially obtained with a tie-back. Second, we plan to quantitate the degree of airway contamination by feed material after both surgical procedures. Third, we propose to evaluate if feeding from the ground reduces tracheal contamination after each surgical procedure.