Electromyographic and histologic evolution of the recurrent laryngeal nerve from transection and anastomosis to mature reinnervation.

OBJECTIVES To describe the natural evolution of recurrent laryngeal nerve (RLN) reinnervation in an animal model. STUDY DESIGN Twenty Sprague Dawley rats underwent unilateral RLN transection and anastomosis. Animals were sacrificed at 4, 8, 12, 16, and 20 weeks. Prior to sacrifice, each rat underwent electromyography (EMG) and visual grading of vocal fold motion. Bilateral RLNs were harvested and evaluated histologically. RESULTS EMG revealed synkinetic reinnervation at all time periods except at 4 weeks. EMG evolution plateaued at 16 weeks. Vocal fold motion was slight in three rats at 4 weeks but was otherwise absent except for one rat at 12 weeks. Histologic changes of the axons and their myelin sheaths were consistent at each time period. At 16 weeks, histologic changes plateaued. CONCLUSIONS Consistent EMG, histologic, and vocal fold motion changes occur at specific time periods during RLN reinnervation after transection and anastomosis in a rat model. Reinnervation is mature at 16 weeks. Findings corroborate theories of preferential and synkinetic reinnervation after RLN transection. Use of a rat model to investigate the effect of interventions on RLN reinnervation requires a minimum of 16 weeks between transection and investigation to allow for maturation of reinnervation.