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Purpose of the study: To compare the predictive value of ultrasonography in comparison to resting endoscopy regarding laryngeal function during overground endoscopy.
Methods: 59 warmbloods were examined clinically, ultrasonographically, endoscopically at rest and during overground endoscopy. The ultrasonographic examination was performed using a standardized preset and a linear probe (L8-18i, General Electrics, Connecticut, USA). Production of bilateral transversal images of the lateral cricoarytenoid muscle (CAL) was feasible in all horses. Endoscopic laryngeal functions at rest and during overground endoscopy, as well as ultrasonographic findings were scored by three experienced, blinded observers. Additionally, grey-scale analysis of CAL muscle tissue was performed.
Results: Laryngeal ultrasonography proved to be a sensitive diagnostic technique for the diagnosis of recurrent laryngeal neuropathy (RLN) in warmbloods, in particular in young horses. A high correlation of ultrasonographic and endoscopic findings at rest with and without sedation was found (sensitivity up to 100% in horses ≤ 5 years). Sensitivity and specifity were 73 and 88% for transversal measurements compared to overground endoscopy (p = 0.0025). Results of grey-scale analysis exceeded subjective scoring with a sensitivity of 66% and specifity of 100%. Nevertheless, ultrasonography did not have a higher predictive value for laryngeal function during exercise compared to resting endoscopy. Conclusions: Dynamic RLN cannot be surely predicted by resting endoscopy. Laryngeal ultrasonography can be recommended as an additional diagnostic tool, but cannot replace overground endoscopy. In cases of doubt during resting endoscopy of for decision about surgical treatment, endoscopy during exercise remains the gold standard.