Endoscopic Diagnosis in the Upper Airways

Resting endoscopic examination has for decades been used to identify abnormalities in the equine upper respiratory tract (URT). However, most abnormalities in the URT are only visibly during exercise. Over ground endoscopy (OGE) is today the golden standard when evaluating the upper airway and URT abnormalities in ridden horses, and in addition, OGE also implements the effect of the rider and environment. Abnormalities best diagnosed during exercise include displacement of the soft palate and pharyngeal collapse. During OGE the severity of laryngeal neuropathy can better be gauged.

In healthy ridden horses in different head-neck-position both persistent and intermittent changes in larynx and pharynx can be seen without any influence on the performance of the horse. Persistent changes in the larynx and pharynx of horses include pharyngeal lymphoid hyperplasia (PLH) of different grades, oedema in the pharynx, constant lateral instability of the pharynx, flaccid epiglottis and recurrent laryngeal neuropathy (RLN). Intermittent change in the larynx and pharynx can be palatal instability (PI), pharyngeal collapse (PC), medial deviation of the aryepiglottic folds (MDAF), dorsal instability of the pharynx and visible cricotracheal ligament.

Still resting endoscopy can be used for some diseases but often the resting endoscopy has to be combined with over ground endoscopy. Many horses tolerate an endoscopic examination without sedation, but some require a sedative. In these cases, it is important to remember that sedation with detomidine or acepromazine changes the endoscopic picture of the upper airways and can lead to incorrect or missed diagnosis, especially of RLN.

Exercise test on high-speed treadmill is still a valuable tool especially for a more standardized performance test regarding speed, distances and inclination.

Conclusion: Every abnormalities in the URT should be correlated with the performance history of the horse, not to interpret clinical healthy horses as diseased horses.