Intraoperative somatosensory evoked potential findings in acute and chronic spinal canal compromise

Study Design. Early and long-term postoperative outcome were analyzed by re trospective record review and compared with results of intraoperative somat osensory evoked potential (SEP) findings in 70 patients with chronic lumbar stenosis. Summary of Background Data. Adverse SEP changes occur in up to 2% of patien ts during scoliosis surgery and may reverse with intraoperative interventio n. Little is known about the short- or long-term results of intraoperative intervention based on adverse SEP changes in patients with chronic lumbar s tenosis during lumbar decompression and fusion. Objective. To compare intraoperative SEP changes with immediate and long-te rm neurologic outcome in patients undergoing lumbar decompression, instrume ntation and fusion for chronic lumbar stenosis and to determine whether the early correlation between intraoperative SEP deterioration and clinical ou tcome persisted. Methods. Monitoring SEPs using an alternating arm and leg stimulation parad igm allowed rapid identification of intraoperative changes. Retrospective r ecord review was conducted without knowledge of intraoperative SEP findings . Clinical and SEP findings were then compared, to determine whether the st rong association between intraoperative SEP results and early clinical outc ome persisted. Results. Nine of 12 patients who had unilateral intraoperative SEP deterior ation that resolved with intervention had no adverse sequelae; the remainin g three had new ipsilateral weakness that persisted during a 9-24-month fol low-up. Intraoperative SEPs deteriorated in 15% of patients with normal and abnormal baseline SEPs. Intraoperative SEP deterioration could not be pred icted by preoperative radicular pain, focal symptomatology or baseline SEP findings. 80% of patients with normal SEPs but only 54% with abnormal SEPs had immediate and sustained pain relief. SEP deterioration that reversed wi th surgical intervention or high-dose steroids resulted in no adverse neuro logic outcome. Conclusions. Acute, unilateral, unresolved intraoperative SEP deterioration was associated with long-term ipsilateral weakness not predicted by clinic al or neurologic findings before surgery. Clinical improvement persisted in 92% of patients, 4% were unchanged, and 4% had persistent neurologic chang es during an average 12-month follow-up period. The findings underscore the need for monitoring SEPS during surgery in all patients undergoing invasiv e lumbar surgery and for rapid identification and intervention should a uni lateral SEP change persist.