Functional and histopathologic evidence of laryngeal reinnervation using the spinal accessory nerve in horses

OBJECTIVE: To evaluate functional and histopathologic outcomes of standing selective laryngeal reinnervation using the spinal accessory nerve (SAN) in horses with experimentally induced recurrent laryngeal neuropathy (RLN). ANIMALS: Five Thoroughbred mares. STUDY DESIGN: Prospective cohort study. METHODS: The horses underwent left recurrent laryngeal neurectomy followed 8 weeks later by selective laryngeal reinnervation using the SAN. Follow-up evaluations at 4.5, 6, 8, and 12 months included treadmill exercising endoscopy, ultrasonography of intrinsic laryngeal muscles, and percutaneous electrical stimulation of the SAN. Twelve months postoperatively, the horses were euthanized for macroscopic and histopathologic examination of the cricoarytenoideus dorsalis (CAD), cricoarytenoideus lateralis (CAL), sternomandibularis (SM), spinal accessory and recurrent laryngeal nerves. RESULTS: Twelve months following laryngeal reinnervation, mean left-to-right quotient angle ratio (LRQ) recovered to 94% of predenervation values with no difference from the baseline (95% CI [90, 98]; p = .69). One horse exhibited a slower and incomplete recovery. Post-mortem examination confirmed successful spinal accessory nerve implantation in the left CAD muscle in all horses. Histopathologic examination revealed axonal regeneration of the spinal accessory nerve and reinnervation of the left lateral CAD muscle belly with fiber type grouping and a shift toward an increased proportion of type I fibers consistent with functional reinnervation. CONCLUSION: Selective laryngeal reinnervation using the spinal accessory nerve restored functional arytenoid abduction at exercise in 4/5 horses with experimentally induced RLN. CLINICAL SIGNIFICANCE: In horses with RLN and mild to moderate CAD muscle atrophy, selective laryngeal reinnervation using the SAN represents a physiological and effective treatment option.