Paradoxical movement of rat vocal folds following recurrent laryngeal nerve injury

Objective: To establish a rat model with paradoxical vocal fold movement to understand the detailed etiology and physiology of laryngeal synkinesis by evaluating vocal fold movement and by electromyography. Methods: Adult Wistar rats were used. The recurrent laryngeal nerve was transected, anastomosed, and the anastomotic portion was placed in a silicone tube. At 2, 4, and 10 weeks after the treatment (n = 30), we performed laryngoscopy and electromyography. The vocal fold movement was recorded, the hemiglottal area was measured, and the Darea was calculated by subtracting the area during expiration from that during inhalation. We evaluated the ratio of the Darea on the treated side to that of the normal side. After laryngoscopy, electromyography of the thyroarytenoid and posterior cricoarytenoid muscles was performed. Results: The mean Dareas were 1.5 +/- 3.4%, 2.3 +/- 21.5%, and 0.7 +/- 31.8% at 2, 4, and 10 weeks after anastomosis, respectively. Eighteen of 18 rats indicated synkinetic reinnervation at 4 and 10 weeks. Regarding vocal fold mobility, 8 of 18 animals showed paradoxical movement, and 5 of 18 exhibited impaired mobility. Conclusion: We have established an animal model of paradoxical movement following recurrent laryngeal nerve injury. This model may be useful in studying laryngeal synkinesis.