Spinal evoked potential (SEP) obtained by stimulation on the median nerve--experimental and clinical studies.

The present study was done experimentally and clinically to measure the segmental spinal evoked potential (SEP) of the cervical cord, stimulated on the median nerve, to try to determine the location and severity of cord lesion in patients with cervical spondylotic myelopathy. SEP in control subjects consisted of two waves. The primary reactive wave (R wave) consists of both the nerve root potential and the funiculus posterior potential. The secondary reactive wave (N wave) consists of the post-synaptic potential in the spinal cord. With regard to cervical spondylotic myelopathy, in the early stages the N-wave weakens or disappears at the level of lesion, then, as damage progresses, the R-wave also weakens or disappears.