Not paralysis, but dystonia causes stridor in multiple system atrophy

TLDR

Electromyography was performed on 10 multiple system atrophy patients with laryngeal or pharyngeal symptoms. EMG revealed persistent tonic activity in both abductor and adductor vocal‑cord muscles in stridor patients, and botulinum toxin injection reduced this activity and improved symptoms, indicating that stridor in multiple system atrophy is caused by vocal‑cord dystonia.

Abstract

Electromyography (EMG) was performed in 10 patients with multiple system atrophy, laryngeal or pharyngeal symptoms, or both. In patients with stridor, EMG during quiet breathing revealed persistent tonic activity in both abductor and adductor vocal cord muscles. In patients with dysphagia, the cricopharyngeal muscle showed persistent EMG activity throughout all phases of swallowing. Botulinum toxin injection into the adductor muscle determined subjective improvement and reduced tonic EMG activity. Therefore, the cause of stridor in multiple system atrophy is dystonia of the vocal cords.