A 9 year old racing Thoroughbred gelding presented to Cornell University Equine Hospital on August 5th, 2013 for evaluation and surgical correction of left-sided laryngeal hemiplegia diagnosed by the primary veterinarian. The patient had a history of poor performance since his most recent race 2 months prior to presentation, which he won. Endoscopy was performed by the primary veterinarian and laryngeal hemiplegia was diagnosed.

On presentation, physical examination abnormalities included decreased airflow through the left nostril and ptosis of the left upper palpebra. Laryngeal palpation revealed mild atrophy of the left cricoarytenoideus dorsalis muscle. Endoscopic evaluation of the larynx was performed and grade 3.3 left laryngeal hemiplegia was noted. Trans-esophageal ultrasound of the larynx was performed and minimal atrophy and fibrosis of the left cricoarytenoideus dorsalis muscle was noted which suggested acute onset of paralysis, consistent with the history. The horse was diagnosed with Horner’s syndrome and left laryngeal hemiplegia, most likely due to peri-jugular injection.

This report will discuss the case in detail including the diagnosis and surgical correction of laryngeal hemiplegia. It will also discuss the pathophysiology, common etiologies, clinical presentation, diagnosis, and possible treatment of Horner’s syndrome in the horse.