Morphometric study of nucleus ambiguus in multiple system atrophy presenting with vocal cord abductor paralysis

Aim: Tc, identify lesions responsible for vocal cord abductor paralysis (VC AP) in multiple system atrophy (MSA), we performed a morphometric study of the nucleus ambiguus which innervates the intrinsic laryngeal muscles. Meth ods: Two autopsied cases of MSA presenting with VCAP and one control were e xamined. Both cases of MSA showed selective neurogenic atrophy of the poste rior cricoarytenoid muscles among the intrinsic laryngeal muscles, while no abnormalities were seen in the control. From a block of the medulla oblong ata, sections 10 mu m thickness were cut serially without spacing and stain ed with cresyl violet. The ambiguus neurons were counted in all the section s to make a histogram. Results: In the control case, ambiguus neurons showe d densely populated areas and sparsely populated areas alternately with sig nificant difference in the mean neuronal density between two areas. In MSA, ambiguus neurons were significantly decreased in number at all levels. It indicates that the neurogenic atrophy of the posterior cricoarytenoid muscl e is derived from the neuronal boss of the nucleus ambiguus. Conclusion: Th ough it has still been controversial whether or not the ambiguus neurons ar e decreased in number in MSA with VCAP, we: speculated possible reasons for the disagreement on the involvement of the nucleus ambiguus as follows: di fferent mechanism of VCAP are playing role, and histometric data have been disturbed by factors such as split-cell counting error and marked variation in the distribution of the ambiguus neurons.