Perhaps your horse's performance is lacking, or maybe he sounds like a freight train as he labors through work. He could be suffering from left recurrent laryngeal neuropathy, commonly known as roaring. But how can you get a diagnosis quickly and easily?
The results of a study carried out at Rood & Riddle Equine Hospital in Lexington, Ky., indicate that ultrasonography, in addition to traditional endoscopy methods, can be a supplemental resource for veterinarians to definitively diagnose roaring, one of the leading causes of poor performance in athletic horses.
In a roarer, the muscles that open and close the left side of the larynx as the horse breathes are atrophied, causing the arytenoid cartilage (which closes over the trachea when a horse swallows) to droop into the left side of the airway. This effectively blocks the flow of air into the lungs.
"Resting endoscopy (when an endoscope is passed through the standing horse's nostrils into his throat to provide a view of the internal structures) is often used to evaluate the upper airway and arytenoid cartilages; however, it is not always accurate in predicting which horses will have impaired arytenoid function during exercise," explained Katherine Garrett, DVM, from the diagnostic imaging department at Rood & Riddle.
Conversely, dynamic upper airway endoscopy, which involves assessing the airway of horses during exercise on a high speed treadmill, solves that problem, but the cost is sometimes prohibitive, according to Garrett .
The team hypothesized that an ultrasound exam of the cricoarytenoideus lateralis muscle--one of the arytenoid cartilage muscles--could provide an alternative method for diagnosing roaring.
Garrett et al. reviewed the medical records of 79 Thoroughbreds aged 2 years and up that underwent both resting and dynamic upper airway endoscopy and an ultrasound exam of the larnyx. Veterinarians compared arytenoid cartilage movement observed during the dynamic examination to the resting endoscopy and laryngeal ultrasonography results.
"Abnormal left arytenoid movement (associated with roaring) noted in the dynamic examination was associated with characteristic changes on the ultrasound," Garrett explained. "Specifically, the left cricoarytenoideus lateralis muscle was more hyperechoic (dense) when compared to the right cricoarytenoideus lateralis muscle."
The team also reported that laryngeal ultrasound had a sensitivity of 90% and a specificity of 98% for predicting the horse's likelihood to roar during exercise. In contrast, resting endoscopy was only 80% sensitive and 81% specific. Specificity refers to the probability that the test will be negative among patients who do not have the disease, and sensitivity indicates the probability that the test will be positive when given to a group of patients with the condition.
"These results suggest that a laryngeal ultrasound examination is highly accurate for diagnosing roaring and is a valuable noninvasive tool when investigating abnormalities of the upper airway," concluded Garrett.
The study, "Association of treadmill upper airway endoscopic evaluation with results of ultrasonography and resting upper airway endoscopic evaluation," is scheduled to be published in an upcoming edition of the Equine Veterinary Journal. The abstract is available online.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.
