Myopathology of the intrinsic laryngeal muscles in neurodegenerative diseases, with reference to the mechanism of vocal cord paralysis

To investigate the mechanism of the vocal cord abductor paralysis (VCAP) in the neurodegenerative diseases, the intrinsic laryngeal muscles (the crycothyroid, the interarytenoid, and the posterior crycoarytenoid muscles) from 41 autopsied cases were histologically examined: 10 cases of amyotrophic lateral sclerosis (ALS), 10 of Parkinson's disease (PD), 9 of multiple system atrophy (MSA), 4 of Machado-Joseph disease (MJD), 4 of progressive supranuclear palsy (PSP), 1 of familial amyloidotic polyneuropathy (FAP), and 3 of cerebrovascular diseases as a control. According to the distribution of the neurogenic changes among above-described three intrinsic laryngeal muscles, three forms were raised: 1. The totally paralytic form showing that all the three muscles developed neurogenic atrophy. This form includes ALS, MJD, and FAP. 2. The posterior muscle-paralytic form showing that only the posterior crycoarytenoid muscle was selectively involved. This form includes MSA. 3. The nonparalytic form showing no morphological abnormalities in any of the intrinsic laryngeal muscles. This type includes PD and PSP. In this nonparalytic form, supranuclear mechanism such as pyramidal or extrapyramidal tract involvement may cause VCAP through the increased laryngeal muscles tone. Considering that VCAP can be seen in any of the above-described forms, our results indicate that the mechanism of VCAP is different among the neurological disorders.