Laryngeal stridor in multiple system atrophy: Clinicopathological features and causal hypotheses

Laryngeal stridor is recognized as a characteristic clinical manifestation in patients with multiple system atrophy (MSA). However, the pathogenic mechanisms underlying this symptom are controversial. Neurogenic atrophy of the posterior cricoarytenoid muscle has been identified in cases of MSA, suggesting that laryngeal abductor weakness contributes to laryngeal stridor. However, dystonia in the laryngeal adductor muscles has also been reported to cause laryngeal stridor. Depletion of serotonergic neurons in the medullary raphe nuclei, which exert tonic drive to activate the posterior cricoarytenoid muscle, has recently been identified in MSA cases. This adds weight to the possibility that laryngeal abductor weakness underlies laryngeal stridor in MSA. Continuous positive airway pressure therapy is currently used in the treatment of laryngeal stridor, but should be used with caution in patients showing contraindications. Current knowledge of the clinical and neuropathological features of laryngeal stridor is summarized in this paper, and the hypothesized causes and possible therapeutic options for this symptom are discussed.