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

Early and long-term postoperative outcome were analyzed by retrospective record review and compared with results of intraoperative somatosensory evoked potential (SEP) findings in 70 patients with chronic lumbar stenosis.

Adverse SEP changes occur in up to 2% of patients during scoliosis surgery and may reverse with intraoperative intervention. Little is known about the short- or long-term results of intraoperative intervention based on adverse SEP changes in patients with chronic lumbar stenosis during lumbar decompression and fusion.

To compare intraoperative SEP changes with immediate and long-term neurologic outcome in patients undergoing lumbar decompression, instrumentation and fusion for chronic lumbar stenosis and to determine whether the early correlation between intraoperative SEP deterioration and clinical outcome persisted.

Monitoring SEPs using an alternating arm and leg stimulation paradigm allowed rapid identification of intraoperative changes. Retrospective record review was conducted without knowledge of intraoperative SEP findings. Clinical and SEP findings were then compared, to determine whether the strong association between intraoperative SEP results and early clinical outcome persisted.

Nine of 12 patients who had unilateral intraoperative SEP deterioration that resolved with intervention had no adverse sequelae; the remaining three had new ipsilateral weakness that persisted during a 9-24-month follow-up. Intraoperative SEPs deteriorated in 15% of patients with normal and abnormal baseline SEPs. Intraoperative SEP deterioration could not be predicted 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 with surgical intervention or high-dose steroids resulted in no adverse neurologic outcome.

Acute, unilateral, unresolved intraoperative SEP deterioration was associated with long-term ipsilateral weakness not predicted by clinical or neurologic findings before surgery. Clinical improvement persisted in 92% of patients, 4% were unchanged, and 4% had persistent neurologic changes during an average 12-month follow-up period. The findings underscore the need for monitoring SEPs during surgery in all patients undergoing invasive lumbar surgery and for rapid identification and intervention should a unilateral SEP change persist.