Progressive sequential development of left and right-sided idiopathic recurrent laryngeal neuropathy in a Standardbred racehorse

A 4-year-old Standardbred racehorse presented to the hospital due to poor performance and abnormal respiratory noises. A high-speed treadmill videoendoscopic examination including tracheal airway pressure measurements was performed. Grade C left recurrent neuropathy was diagnosed and a prosthetic laryngoplasty was performed. Following surgery, the horse went back into training and eventually racing and performed well in its first two starts. Ten and a half months later the horse re-presented with abnormal respiratory noise, and poor performance had returned. Therefore, the examination was repeated. This revealed that the left arytenoid cartilage was in a similar abducted position as immediately after prosthetic laryngoplasty surgery. However, right-sided arytenoid paresis was present as well as bilateral aryepiglottic fold collapse and right vocal fold collapse. Bilateral aryepiglottic fold resection and right vocal cordectomy was performed using a diode laser under standing sedation. The horse presented a third time, four and a half months later. At this point, the horse had developed right arytenoid paralysis, and it was euthanised. Necroscopy and histopathological examinations were performed. The right cricoarytenoideus dorsalis muscle was moderately reduced in size and showed signs of denervation atrophy. There was loss of normal myelinated fibres of both recurrent laryngeal nerves as well as evidence of active degeneration of the right recurrent laryngeal nerve. In the way the horse sequentially developed first left-sided then right-sided arytenoid paralysis, combined with histological evidence of nerve degeneration, a diagnosis of ‘clinical’ bilateral idiopathic recurrent laryngeal neuropathy was established.