Observations of recurrent laryngeal nerve injury and recovery using a rat model

Abstract

To evaluate standardized recurrent laryngeal nerve (RLN) injuries using a rat model via minimally invasive transoral electromyography (ToL EMG) and histologic studies. Forty-two female Sprague Dawley rats weighing 200 g to 250 g underwent crush injury to the right RLN using a calibrated pressure clip (0.61 N or 1.19 N) for 60 seconds. Following injury, serial ToL EMGs were performed on abductor and adductor laryngeal muscles during respiratory cycles and spontaneous vocal fold abduction on day 4 and then weekly for 6 weeks. Vocal fold motion associated with spontaneous respiration was graded from 0 to 4. Rats were sacrificed at different time points for histologic evaluation of injured nerves. EMG signals showed fibrillation potentials on day 4 in all experimental conditions. Crushed RLN, regardless of force, exhibited polyphasic potentials at 2 weeks postinjury. Normal motor unit potentials and recruitment patterns were observed in EMG signals at 4 weeks for all 0.61 N clip animals. Six weeks following crush injury, motor unit potentials having normal appearance were observed in most animals. Synkinetic EMG signals were observed at 5 weeks and 6 weeks in the 1.19 N clip animals. Endoscopic evaluation of vocal fold mobility was consistently normal at 6 weeks only following 0.61 N crush injury. This model is useful to simulate intraoperative RLN injuries and to better understand the electrophysiologic events during nerve recovery. The severity of injury to the RLN dictates histologic, neurologic and functional recovery of the laryngeal motor system. This model is useful to evaluate the efficacy of systemic and local neurotropic agents in the treatment of RLN injury.