Different mechanism of vocal cord paralysis between spinocerebellar ataxia (SCA 1 and SCA 3) and multiple system atrophy.

While multiple system atrophy (MSA) is frequently associated with vocal cord paralysis (VCP) causing severe respiratory failure, it is still unknown whether hereditary types of spinocerebellar degeneration develop similar laryngeal paralysis. We analyzed the laryngeal function from the viewpoints of fiberoptic laryngoscopy and laryngeal myopathology and then attempted to clarify the difference of the mechanism of VCP among the patients with spinocerebellar ataxia type 1 (SCA 1), type 3 (SCA 3), and MSA. Seven patients with SCA 1, nineteen with SCA 3, and eleven with MSA were studied. Vocal cord movement was analyzed by fiberoptic laryngoscopy during wakefulness and diazepam-induced sleep (sleep load test). Paraffin-embedded sections or cryosections of the intrinsic laryngeal muscles from five autopsied cases (one with SCA 1 and four with SCA 3) were histologically examined. VCP was found in two of the seven SCA 1 patients (29%), three of the nineteen SCA 3 patients (16%), and in nine of the eleven MSA patients (82%). VCP observed in SCA 1 and SCA 3 was various in the severity and showed no exacerbation on sleep load test in all of the eight patients but one SCA 3 patient. In this patient, the findings of fiberoptic laryngoscopy were quite similar to those found in MSA. All the intrinsic laryngeal muscles including cricothyroid (CT), interarytenoid (IA), and posterior cricoarytenoid (PCA) muscles showed neurogenic atrophy in one autopsied SCA 1 and four SCA 3 patients. Our conclusion is that VCP in SCA 1 and SCA 3 contrasts with that in MSA in its occurrence, response to the sleep load test, and the distribution of the neurogenic abnormalities among the intrinsic laryngeal muscles.