Epiglottic Entrapment in the Racing Thoroughbred
by Dr. Gregory L. Ferraro
The racing Thoroughbred thoughtfully pursed the condition known as “entrapped epiglottis” for the expressed purpose of making the veterinary profession look good: it is one of the few equine upper respiratory tract maladies that we can actually correct with regularity.
The epiglottis is a cartilage that covers the entrance to the larynx and serves to prevent food from entering the larynx and trachea while swallowing. Epiglottic entrapment occurs when the epiglottis becomes trapped in a fold of tissue (aryteno-epiglottic fold) on the floor of the pharynx. This situation somewhat mimics your hand in the pocket of a tight pair of jeans. Sometimes, it is difficult, if not impossible, to remove your hand. Likewise, in the horse, the condition can be intermittent or permanent in its entrapment and it adversely affects performance. A clinician diagnoses this condition through endoscopic examination of the upper respiratory tract.
Unlike most other equine larynx and pharynx conditions, epiglottic entrapment is not characterized by noise production. In fact, these horses generally make no noise during exercise or competition. However, riders often report that horses with this condition cough violently or act as if they are choking when pulled up after a race or workout. The coughing fit occurs because the movement of the epiglottis (which must seal off the airway during swallowing) is impaired. Consequently, horses cannot accomplish the quick reflex swallowing necessary to clear the pharynx of secretions during high-speed exercise. These secretions build up, enter the windpipe and stimulate the choking-like syndrome after the animal has stopped. The excess secretions may also contribute to the resulting poor performance.
Jockeys also report that affected horses occasionally appear to hold their breath during competition and exhibit a great exhalation sigh when pulled up. Horses must accomplish both inspiration and expiration within the confines of each stride cycle. With an epiglottic entrapment, the free border of the entrapping tissue balloons up during expiration, but not during inspiration. This effectively creates a one-way flutter valve that impairs the flow of exhaled gases, but not the flow of inhaled gases. As a result, at every stride, the horse inhales more air than it can exhale, resulting in the gradual buildup of reserve gas within the lung. This gradual expansion of the chest, combined with the expiratory rush at the end of the race, leads riders to believe the horse is holding its breath. This syndrome results in impaired racing performance.
The origin of epiglottic entrapment is readily explained. All horses have a fold of tissue on the floor of their pharynx known as the aryteno-epiglottic fold. Only the ones who love their veterinarians manage to get their epiglottis entrapped in this fold. Inflammation, either through infection or tissue trauma, causes this fold to swell. Once this inflammation has progressed sufficiently, the epiglottis becomes entrapped due to the swelling and is unable to extricate itself.
Mild and early cases often can be resolved in two to three weeks through medical treatment and rest. Agents are systemically and topically administered (via pharyngeal sprays) to counteract the infectious processes and relieve the inflammation. Surgical correction is required for more advanced and persistent cases of entrapment or for the mild cases that consistently recur. You are in luck here, however, because unlike most other conditions of the equine pharynx and larynx, surgical correction usually returns the horse to full function in a relatively short period of time.
Two basic surgical procedures are used to correct an entrapped epiglottis in the horse. Each procedure has advantages and disadvantages, but both are acceptable. The first involves entering the horse’s pharynx either through the mouth and/or the nose and incising the fold at its midpoint. A surgeon can accomplish this procedure fairly quickly using a blade-type instrument specifically designed for this procedure or with a surgical laser apparatus. Both tools accomplish the task well and after a period of convalescence, most horses readily return to full work.
This method’s major disadvantage is that the epiglottic entrapment recurs in a significant percentage of operated horses (perhaps 25%) because you are only splitting the entrapping fold, not removing it. If the fold heals back together and has cause to swell again, re-entrapment of the epiglottis can result.
Another disadvantage to this method is the length of time required for recovery. When the entrapped tissue is infected or grossly thickened, surgery should not be performed until the horse is treated medically and the aryteno-epiglottic fold becomes more benign in nature. This is especially true when using a surgical blade. The pre-surgical treatment often requires an extended time period to achieve the desired status resulting in a delayed surgical resolution. Likewise, this method often requires an extended post surgical treatment period because all tissue inflammation and swelling must resolve itself before training can resume. Also, some entrapments are not amenable to this surgical procedure. For horses whose epiglottis is only partially or intermittently entrapped by the fold, this procedure is not always effective.
The second surgical correction for epiglottic entrapment involves entry through the floor of the pharynx and removal of the entire aryteno-epiglottic fold. A major advantage of this method is that, regardless of the stage of infection or inflammation, almost any fold can be removed, including partial or intermittent entrapments. Consequently, there is no delay in the surgical correction. Following removal of the fold, horses generally return to full training within two to three weeks; therefore, this method often results in less down time than with the first procedure. The biggest selling point for this method, however, is that post-surgical re-entrapment is not possible because the entire fold is removed.
The disadvantages of this technique include a slight increase in the risk and cost. Because this procedure requires general anesthesia, it carries more inherent risk to the horse and is more expensive to perform. On the other hand, general anesthetic techniques in the horse are fairly well advanced so the risk may be considered minimal for most healthy animals. In regard to owner expense, although the surgery itself may cost more, the total lay-up time might turn out to be less. As a result, the overall financial impact may be about the same for both procedures.
Another disadvantage to this method is that many surgeons are not as familiar with this technique; consequently it may not be a readily available option. And finally, in a small percentage of cases, some transient dorsal displacement of the soft palate occurs following surgery. However, in almost every case reported, the displacement corrected itself within three to six weeks and therefore constitutes more of a nuisance than a real problem.
Overall, when racehorses develop epiglottic entrapment, owners can expect the condition to be corrected and the horse’s performance to be restored. There is one catch, however. (You didn’t expect this to be that easy did you?) If the underlying reason the epiglottis became entrapped was because the epiglottis itself was abnormally small rather than because the aryteno-epiglottic fold became swollen, then (in terms of racing performance) full recovery may not result. An abnormally small epiglottis can occur as a developmental defect or as the result of an infection or insult to the epiglottis itself.
The epiglottic cartilage is much like a prizefighter’s ear. If subjected to sustained punishment, infection or inflammatory insult, the cartilage has a tendency to shrivel in size. Once the horse’s epiglottis shrinks, optimum athletic performance will be prevented due to chronic dorsal displacement of the soft palate or other permanent maladies. While this is not common in cases of epiglottic entrapment, it does occur, particularly when Infection and entrapment have persisted untreated for extensive periods of time. Ask your veterinarian; often, he or she can warn you ahead of time if this problem is suspected.
So, my friend, the next time your trainer tells you that your horse has a respiratory problem, wish for an epiglottic entrapment! It’s one of the best things that can happen to your horse because, most likely, it can be corrected.
Horses with Epiglottic Entrapment conditions are generally Insurable - but there will be an exclusion on horses that are insured After the fact, since it is pre-existing.