Somatosensory evoked potentials in evaluation of decompressive surgery of cervical spondylosis and herniated disc

Somatosensory evoked potentials (SEPs) were studied in patients with cervical radiculopathy and/or myelopathy caused by spondylosis or herniated disc. SEP-recordings were performed before and after operation using an averaging technique by stimulating the median nerve separately at both wrists, with surface electrodes at three different levels: Erb's point, 7th cervical spine and inion. During the follow-up time all patients showed improvement of clinical symptoms. The preoperative SEP recording was abnormal in one or more parameters in all patients. Notable improvement (6-36 months postoperatively) of these abnormalities was observed in 12 out of 14 radiculopathy patients and in 4 out of 9 myelopathy patients. Only in the radiculopathy series could a statistically significant improvement (p less than 0.01) be found in two SEP parameters (amplitude N13 and relative amplitude difference of N13 amplitude). Therefore SEP abnormalities are commonly present in cervical radiculopathy and particularly in cervical myelopathy, and seem to be quite persistent postoperatively, even though clinical improvement especially in the form of pain relief is achieved.