Intraoperative use of dermatomal somatosensory-evoked potentials in lumbar stenosis surgery.

This report concerns the use of dermatomal somatosensory-evoked potentials (DSEPs) for intraoperative monitoring in the surgical management of a group of patients with lumbar spinal stenosis. Thirty patients with lumbar spinal stenosis underwent preoperative evaluation by DSEPs by use of electrical stimulation of the skin corresponding to the L4, L5, and S1 dermatomes. The specific dermatome to be monitored intraoperatively was selected by correlating those data with physical and radiographic findings and, in certain cases, the results of selective nerve root blocks. Intraoperative baseline (predecompression) DSEP values were obtained after positioning the patient on the operative frame. Monitoring was performed during surgery and post-decompression values were obtained after neural decompression. For six cases of unilateral nerve root decompression, an average 9-msec decrease in latency was noted on the operated side and a 3-msec decrease on the nonoperated side. For 24 cases of bilateral decompression, an average 8-9-msec decrease in latency was noted bilaterally. This method has been found helpful in assessing the adequacy of neural decompression intraoperatively.