On the basis of electromyography, radiography and ultra-high speed cinematography, vocal cord paralysis can be classified into three groups. In the first group (paralytic type), regeneration can not be expected and the mobility of the vocal cord is completely lost. In these cases, no electrical activity is found. Marked atrophy of the vocal cord on the diseased side is noticed. Glottis is opened during phonation and the vibration of the vocal cord, is irregular, asymmetrical and markedly weak. In the second group (paretic type), normal neuromuscular unit voltage is recorded. Atrophy of the paretic vocal cord is very slight and the mobility of the vocal cord is slightly observed. Glottis is closed during phonation and the vibration of both vocal cords is regular and symmetrical or asymmetrical. The voice is not so hoarse. In the third group (pending type), the possibility of recovery remains. In these cases, abnormal electromyograms such as fibrillation voltage are observed. The atrophy of the muscles on the affected side is moderate. Glottis is insufficiently closed during phonation, and the vibration of the vocal cord is irregular. Many of these cases will belong to either of the former two types about one year later from the attack and a few of them will recover.
