Laryngeal abductor paralysis in multiple system atrophy. A report on three necropsied cases, with observations on the laryngeal muscles and the nuclei ambigui.

Clinical and pathological findings are reported in three cases of Shy-Drager syndrome with laryngeal stridor severe enough to require tracheostomy. Indirect laryngoscopy in all three cases revealed a failure to abduct the vocal cords properly with a resulting narrowing of the glottic airway. Histological studies showed a marked atrophy of the posterior crico-arytenoid muscles and little atrophy of the other laryngeal muscles. The posterior crico-arytenoid muscles have the sole responsibility of abducting the vocal cords, so it is concluded that the patient's stridor was caused by the selective paralysis of these muscles. Histological studies of the posterior crico-arytenoid muscles were suggestive of denervation but despite this finding, no clear evidence of any motor cell loss in the nuclei ambigui was obtained. Other possible causes of the selective posterior crico-arytenoid atrophy are discussed.