An experimental study on the laryngeal electromyography and visual observations in varying types of surgical injuries to the unilateral recurrent laryngeal nerve in the neck.

A series of varying types of surgical injuries to the recurrent laryngeal nerve, including half section, double crush, suture ligation, and complete section of the nerve, was investigated in dogs by correlating clinical and electromyographic findings. The state of recovery from palsy was evaluated by recording the electromyography from the affected laryngeal muscles as well as by observing the movements of the vocal cords. Six electromyography patterns were recorded from the affected muscles following injuries to the recurrent laryngeal nerve. There is a close relationship between the electromyography patterns and the types of nerve injuries. Within 3 months after injuries of the recurrent laryngeal nerve, the electromyography motor unit potentials in the involved intrinsic laryngeal muscles and vocal cord movements on the side of the nerve injury were back to normal in the groups of dogs in which the recurrent laryngeal nerves were partially sectioned and doubly crushed; the electromyography potentials and vocal cord motion on the affected side did not return to normal in the group of dogs in which the recurrent laryngeal nerves were permanently ligated with suture. In the group of dogs which had had a complete section of the recurrent laryngeal nerve, no recovery of both electromyography and vocal cord function on the affected side was observed 6 months after injury of the recurrent laryngeal nerve. This study showed that the frequency of the regenerated potentials recorded from the affected muscles is related to the types and degrees of injuries to the recurrent laryngeal nerve. Recovery from recurrent laryngeal nerve palsy is complete within 3 months after nerve impairment if over half of the nerve fibers of the impaired nerve are maintained intact without degeneration. Moreover, the period from onset to complete recovery from palsy was remarkably short, less than 2 months. The most appropriate time for the electromyography examination to evaluate the degrees of the nerve injury and to anticipate the prognosis of recurrent laryngeal nerve palsy was proposed.