Reasons for performing study: Assessment of arytenoid movement has traditionally been performed using upper airway (UA) endoscopy. However, recent work suggests that laryngeal ultrasonography may provide additional complementary information.
Objective: To determine the value of laryngeal ultrasonography for the diagnosis of recurrent laryngeal neuropathy in the horse.
Hypotheses: Horses with abnormal arytenoid movement (AM) during treadmill UA endoscopy would have increased echogenicity of the left cricoarytenoideus lateralis muscle (CALM) and smaller left CALM and vocalis size while horses with normal AM during treadmill UA endoscopy would have normal echogenicity of the left CALM and similar left and right CALM and vocalis muscle size. Laryngeal ultrasonography would be more accurate than resting endoscopy at predicting abnormal AM.
Methods: Medical records were examined to identify Thoroughbred racehorses aged ≥2 years that had undergone resting and treadmill UA endoscopy and laryngeal ultrasonography. Resting and treadmill AM was graded using accepted scales. The treadmill examination was used as the criterion standard for AM. Laryngeal ultrasonography was performed and the relative echogenicity of the left and right CALM and the cross-sectional area (CSA) of the CALM and vocalis muscle determined. Data analysis included Chi-squared tests, paired t tests and one-way ANOVA.
Results: The presence of abnormal AM was associated with relative hyperechogenicity of the CALM while normal AM was not. Laryngeal ultrasonography had a sensitivity of 90% and specificity of 98% and resting UA endoscopy had a sensitivity of 80% and specificity of 81% for diagnosis of abnormal AM. CSA of the left CALM and vocalis muscle was not different between groups.
Conclusions: Laryngeal ultrasonography has high accuracy for diagnosing abnormal AM.
Potential relevance: Ultrasonography is a valuable addition to the diagnostic evaluation of the equine UA.