Somatosensory evoked potentials in the diagnosis of cervical spondylotic myelopathy.

Median, ulnar, radial and common peroneal nerve somatosensory evoked potentials (SEPs) were studied in 17 patients suffering from cervical spondylotic myelopathy. Median, ulnar and common peroneal nerve SEPs were abnormal in 41%, 71% and 100% of cases respectively. Abnormalities of the scalp far-field P14 evoked by upper limb stimulation correlated with joint and touch sensation impairment, but not with radiological findings. Therefore, P14 may be a reliable marker of dorsal column impairment in cervical spondylotic myelopathy. The analysis of the cervical N13 response, which was recorded using a cephalic reference electrode, did not give any further information. Common peroneal nerve SEP abnormalities were found in all our patients, but they were obviously of no value in identifying the cervical spine as the site of lesion.