Segmental dysfunction of the cervical cord revealed by abnormalities of the spinal N13 potential in cervical spondylotic myelopathy

We studied somatosensory potentials (SEPs) evoked by stimulation of radial, median, and ulnar nerves in 11 patients with MRI evidence of cervical spondylosis. All patients presented with progressive spastic paraparesis that was either isolated or associated with lower motor neuron signs in the upper limbs, with preserved joint, touch, pain, and temperature sensations in the four limbs. In all patients, scalp SEPs reflecting the activity of the dorsal column system up to the parietal cortex were normal while segmental cervical cord dysfunction was manifested by an abnormal spinal N13 potential in 95% of radial, 90% of median, and 54% of ulnar nerve SEPs. These subclinical abnormalities of the spinal N13 SEP probably result from reduced blood supply due to compression of the anterior spinal artery in patients with cervical spondylotic myelopathy.