Lower number and thinner myelin of large myelinated fibers in human cervical compression radiculopathy.

The authors conducted a morphometric investigation of the histopathological alterations in myelinated fibers (MFs) of the nerve roots of C-6, which showed macroscopic indentation, presumably due to cervical spondylotic radiculopathy. In six cadavers, designated as the radiculopathy group, in which the nerve roots of C-6 showed indentation due to compression on one side (indented side) and the remaining nerve roots (normal side) showed a normal appearance macroscopically, morphometric findings of the nerve roots and the MFs on both the indented and normal sides were evaluated and subjected to blind comparison. Seven cadavers with normal-appearing C-6 nerve roots served as controls. In the control group, there were no differences in the morphometric parameters: that is, total transverse fascicular area, total number of small and large MFs, and relationship between myelin thickness and the radius of the axon between the right and left sides in either the ventral or dorsal roots. There was no evidence found of axonal degeneration, ongoing demyelination, or loss of MFs in either the ventral or dorsal roots in the radiculopathy group on the indented side. However, there were significantly lower numbers of large MFs per root and significantly thinner myelin sheaths relative to axon size on the indented side compared with those on the normal side in both the ventral and dorsal roots. These findings are characteristic alterations of the MFs produced by chronic low-grade compression.