An electromyographic study of recurrent laryngeal nerve paralysis

Abstract

Electromyographic investigations of the intrinsic laryngeal muscles were carried out in 29 human cases with recurrent laryngeal nerve paralysis and in 14 canine cases, in which unilateral recurrent laryngeal nerve paralysis was experimentally caused by various methods of crushing, section and suture after section of the nerve. The observations in dogs were repeated before the operation and several minutes, several days, a month and every months up to death after causing paralysis. The laryngoscopic view of the position of the vocal cords was compared with the electromyogram in every case.The results obtained are as follows;1. The thyroarytenoid, the lateral cricoarytenoid and the posterior cricoarytenoid muscle of the human larynx are innervated by homolateral laryngeal nerve, and the arytenoid muscle is innervated by bilateral ones. In the canine larynx, however, the arytenoid muscle is separated into two pieces in both sides and innervated by each homolateral recurrent nerve. Some muscle fibers of the cricothyroid is considered to be mixed in the lateral cricoarytenoid in dogs, because the electrical activity of the lateral cricoarytenoid was not ceased after section of the homolateral recurrent laryngeal nerve in some of canine cases.2. The abnormal pattern of electromyogram of laryngeal muscles such as fibrillation voltage, complex NMU voltage or reinnervation voltage was observed in many cases of recurrent laryngeal nerve paralysis. In the course of regeneration of the nerve in canine cases the fibrillation voltage appeared within 5 days after the damage of the recurrent laryngeal nerve and subsequently the complex NMU voltage was developed and it was followed with the reinnervation voltage and the normal NMU voltage.3. No differences among regeneration velocities of the intrinsic laryngeal muscles were noted in the experimental recurrent laryngeal nerve paralysis of dogs. The nerve regeneration velocity is sooner as following order, crushing-group, suture after section-group and section-group.4. The phenomenon of the misdirected regeneration of the nerve was noted in some cases of both human and canine recurrent laryngeal nerve paralysis; i.e., active discharges of the adductor or the abductor of the vocal, cord were recorded during inspiration and expiration as well as phonation. Since the abductor contracts with the adductors during phonation and respiration after. the nerve has regenerated, the involved vocal cord remains to be fixed at paramedian position in some cases of recurrent laryngeal nerve paralysis.5. Electromyographic analysis of all intrinsic laryngeal muscles in cases of so-called musclar such as Internus palsy or Transversus palsy revealed no abnormality of the function in these muscles. It is considered the insufficiency of closure of the glotttis during phonation is caused by the pathological change of the mucous membrane in the subglottic cavity.