HOW TO DIAGNOSE POOR PERFORMANCE IN THE EQUINE ATHLETE


valuable. What has been done, when was it done, and what were the results? Are there any problems with chewing or swallowing? Is there any history of bleeding (e.g., exercise-induced pulmonary hemor- rhage [EIPH])? If so, has the frequency or severity increased? Does the horse compete on furosemide or other medications? In most cases of upper airway obstruction, an abnormal respiratory noise is observed during exer- cise. Lung conditions are not associated with ab- normal breathing sounds during work. However, false negatives for respiratory noise occur. URT obstruction can sometimes present without accom- panying abnormal sound. Abnormal sound can be “drowned out” by ambient noise (pounding hoofs, loudspeakers, machinery, spectators). The rider or trainer can often answer questions more accurately than the owner. An abnormal noise may not be noted until the horse pulls up. If possible, the char- acter (whistle, gurgle, flutter) and timing (inspira- tion vs. expiration) should be ascertained. Billowing of the cheeks or mouth breathing can occur with soft palate displacement. Sudden palate displacement during exercise can cause an abrupt, dramatic de- crease in performance. If an abnormal noise is not heard constantly, when during the exercise does it occur? Does it coincide with a change in perfor- mance? Does it seem to be related to certain condi- tions or maneuvers? Does head position (poll flexion or collection) change the noise? Is coughing or nasal discharge observed? Does the horse sweat normally? Tachypnea and exercise intolerance can be seen with anhydrosis in hot climates. The owner or agent should be asked whether lameness or stiffness is observed during or after work. Musculoskeletal pain can cause tachypnea, poor performance, and behavioral changes.


3. Physical Examination


Even with a history suggestive of a respiratory prob- lem, a cursory exam for lameness and neurologic deficits should not be omitted. At minimum, the horse’s movement is evaluated at the walk and trot, in a straight line, and in circles. In the standing horse, the entire musculoskeletal system should be checked for swelling, atrophy, asymmetry, tender- ness, and heat. During the physical examination of the respiratory tract, symmetry of air movement through both nasal passages should be confirmed. If nasal discharge is seen, it should be characterized and the source of the exudate should be pursued. The face and head should be checked for external swelling or asymmetry of the nasal and sinus re- gions and for evidence of cranial nerve deficit. The larynx and trachea should be thoroughly palpated. Laryngeal palpation is an acquired skill, but with practice, one can become accurate in detecting asym- metry of the caudal portion of cricoarytenoideus dor- salis muscles (CADM) secondary to recurrent laryngeal neuropathy, as well as hypoplasia or ab- normal position of the muscular process of the ary-


194 2018  Vol. 64  AAEP PROCEEDINGS


tenoid cartilage secondary to laryngeal dysplasia.3 The common sites for URT surgery should be checked for previous incisions. Laryngoplasty scars are difficult to detect without clipping the hair from the site. The trachea should be checked for indentation or deformity of the cartilage rings from injury or previous tracheotomy. The jugular veins should be checked for patency. Jugular thrombosis or phlebitis can be associated with vagal or recur- rent laryngeal nerve injury or can cause nasal mu- cosal swelling. The trachea, heart, and lungs should be thoroughly ausculted.


4. Endoscopic Exam at Rest


A resting endoscopic exam of the URT remains the starting point for diagnosis of airway obstruction. Structural abnormalities can be assessed, as well as some functional deficits. Accurately predicting how an abnormality seen in the resting horse affects breathing at exercise can be problematic. The en- doscopic examination should be performed without sedation. Sedation can cause asynchronous move- ment or incomplete abduction of the arytenoid car- tilages. Horses are also more likely to show some degree of pharyngeal collapse at rest when sedated, especially when the nares are manually occluded. Most horses need some physical restraint to be scoped safely, most often accomplished with a rope twitch. A set of stocks provides additional protec- tion to personnel and equipment if available. A complete examination includes visualization of both right and left nasal passages, ethmoid and nasomax- illary regions, nasopharynx (including soft palate), guttural pouches, larynx, and trachea. The nasal passages are best assessed as the scope is with- drawn. Narrowing of either nasal passage can oc- cur with sinus disease or with enlargement or deviation of the nasal septum. Anatomic narrow- ing of the nasopharynx at the level of the guttural pouch openings can predispose the individual to lat- eral pharyngeal collapse at exercise.4 Pharyngeal lymphoid hyperplasia (pharyngitis) is commonly seen in young racehorses. Severe pharyngitis does not directly cause noise or obstruction, but affected horses are more prone to soft palate instability or pharyngeal collapse. The interior of both guttural pouches should be examined for empyema, mycosis, and enlargement of retropharyngeal lymph nodes. These conditions can affect function of the soft palate by causing neuropathy of the vagal and/or glossopharyngeal nerves.5 Nasopharyngeal cica- trix, subepiglottic cysts, pharyngeal cyst/mass, persistent soft palate displacement, persistent aryepiglottic entrapment, epiglottic abscess or defor- mity, laryngeal hemiplegia, arytenoid chondritis, and tracheal stenosis can all be accurately diag- nosed by standing endoscopy. Intermittent dorsal displacement of the soft palate (iDDSP) or palatal instability (PI) cannot be diagnosed by endoscopy at rest. Hypoplasia or flaccidity of the epiglottis does not correlate with increased likelihood of iDDSP or


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