Equine Laryngeal Hemiplegia Study Guide

Overview and Clinical Importance

Laryngeal hemiplegia, also known as recurrent laryngeal neuropathy (RLN) or colloquially as "roaring," is a progressive degenerative neuropathy of the recurrent laryngeal nerve that results in dysfunction of the cricoarytenoideus dorsalis (CAD) muscle. This condition is one of the most common causes of upper airway obstruction and exercise intolerance in performance horses, particularly affecting Thoroughbreds and draft breeds.

The disease predominantly affects the left side (greater than 95% of idiopathic cases) due to the longer course of the left recurrent laryngeal nerve, which loops around the aortic arch before ascending to the larynx. This extended pathway makes the nerve more susceptible to axonal degeneration.

Anatomy and Neuroanatomy

Laryngeal Cartilages

The equine larynx is composed of several cartilages that work together to regulate airflow and protect the airway during swallowing. The arytenoid cartilages are paired, triangular-shaped hyaline cartilages that are the key structures affected in laryngeal hemiplegia. They articulate with the cricoid cartilage via the cricoarytenoid joint, which allows abduction and adduction movements critical for airway control.