Morphometry of the degenerative process in the hypoglossal nerves in amyotrophic lateral sclerosis

The peripheral hypoglossal nerves in 13 cases of amyotrophic lateral sclerosis (ALS) and five control cases were examined using morphometrical methods to demonstrate the degenerative process of motor nerve degeneration. The total number of myelinated fibers and their histograms were analyzed according to the degree of severity of the degeneration. Reduction of the total number of myelinated fibers in ALS hypoglossal nerves were graded in three groups: mild 65%-75%, moderate 50%-65% and severe 30%-50% of the myelinated fibers in controls. Each histogram of the remaining myelinated fibers showed different patterns corresponding to the degree of the degeneration and disclosed that the progressive reduction of large myelinated fibers was the fundamental change. Small myelinated fibers were not reduced, but increased, especially in the group with a moderate grade of degeneration. In plastic section, there were clusters of regenerated myelinated fibers. The transient increase of small myelinated fibers may be a reflexion of myelinated fiber regeneration during the progressive degenerative process of the motor neurons. The correlation between the degree of severity of the hypoglossal nerve degeneration and the atrophy of the tongue muscle and the duration of bulbar symptoms was examined and discussed.