Laryngeal electromyography with separated surface electrodes in patients with multiple system atrophy presenting with vocal cord paralysis

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Abstract
When recording the activity of the posterior cricoarytenoid muscle (PCA) with surface electrodes, there is contamination from the surrounding muscles such as the cricopharyngeal muscle. We therefore devised a new oesophageal catheter electrode of the separate type, having three individual surface electrodes for the PCA, cricopharyngeal muscle and diaphragm. The records obtained with this catheter demonstrated satisfactory separation between PCA and cricopharyngeal muscle activities. We used this catheter in patients with multiple system atrophy presenting with vocal cord paralysis, who were awake or asleep. There were two interesting electromyographical findings, which were inspiratory activity of the adductor muscle (the thyroarytenoid muscle) and fade-out of the abductor muscle, that is, PCA activity during sleep. Although vocal cord paralysis is one of the most serious life-threatening complications, the precise mechanism has not been clarified. We believe that our catheter may be useful in investigating the mechanism of vocal cord paralysis which could cause sudden death in neurodegenerative disorders, including multiple system atrophy.