Objective: To define correlations between vocal cords electromyography (EMG) abnormalities and stridor in multiple system atrophy (MSA) phenotypes.

Background: MSA is a rare α-synucleinopathy characterized by dysautonomia and prevailing parkinsonian (MSA-P) or cerebellar (MSA-C) signs. Stridor is a red flag for MSA, it occurs predominantly during sleep and its daytime onset is associated with greater severity and especially poor prognosis. Controversy over the pathophysiology of stridor in MSA remains ongoing.

Method: We recruited 60 patients with “probable” MSA (45 MSA-P and 15 MSA-C; male/female: 26/34; age at onset: 61.8 ± 7.6 years; disease duration at diagnosis: 4.8 ± 2.2 years). All subjects performed a video-polysomnography (VPSG) to detect nocturnal stridor, and EMG of the adductor thyroarytenoid (TA) and the abductor posterior cricoarytenoid (PCA) muscles. The EMG findings were subdivided into four patterns: I (normal); II (tonic EMG activity of the TA muscle during quiet breathing); III (paradoxical activation of the TA muscle during quiet inspiration); IV (neurogenic pattern on motor unit action potentials analysis of the PCA and/or TA muscles, and paradoxical activation of the TA muscle during quiet inspiration). Eventual diurnal stridor was clinically reported.

Results: VPSG revealed nocturnal stridor in 19 patients (14 MSA-P and 5 MSA-C). Diurnal stridor was recognized in 6 subjects (2 MSA-P and 4 MSA-C). A clear predominance of EMG pattern III was found in MSA-P patients with nocturnal stridor (pattern II: 21.43%; pattern III: 71.43%; pattern IV: 7.14%; p < 0.001). For MSA-C patients with nocturnal stridor, EMG pattern IV was more frequent (pattern III: 20%; pattern IV: 80%; p < 0.05). All MSA-P patients with diurnal stridor showed pattern III (p < 0.05). Among MSA-C patients with diurnal stridor, 25% had pattern III, and 75% had pattern IV, with no significant differences (p > 0.05).

Conclusion: The predominant vocal cords EMG abnormalities of MSA patients with stridor were purely dystonic in MSA-P, and neurogenic-dystonic in MSA-C. In this regard, the pathophysiology of stridor may be different between the two MSA phenotypes, being mostly associated to an abnormal premotor control of laryngeal motoneurons in MSA-P, and to a predominant damage of medulla oblongata in MSA-C.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/vocal-cords-electromyography-abnormalities-in-multiple-system-atrophy-phenotypes-relevance-for-the-pathophysiology-of-stridor/