Loss of lower limb motor evoked potentials and spinal cord injury during the initial exposure in scoliosis surgery

PURPOSE:: To report a case of motor evoked potential changes and spinal cord injury during the initial dissection in scoliosis surgery. METHODS:: Motor evoked potentials to transcranial electrical stimulation were recorded from multiple muscles. Somatosensory evoked potentials to limb nerve stimulation were recorded from the scalp. RESULTS:: Clear motor evoked potentials were initially present in all monitored muscles. The patient was then pharmacologically paralyzed for the initial dissection. More than usual bleeding was encountered during that dissection, prompting transfusion. As the neuromuscular blockade subsided, motor evoked potentials persisted in the hand muscles but disappeared and remained absent in all monitored leg muscles. The spine had not been instrumented. A wake-up test demonstrated paraplegia; the surgery was aborted. There were no adverse somatosensory evoked potential changes. MRI showed an anterior spinal cord infarct. CONCLUSIONS:: Copious soft tissue bleeding during the initial dissection might have lowered pressures in critical segmental arteries enough to cause spinal cord infarction through a steal phenomenon. The lack of somatosensory evoked potential changes reflected sparing of the dorsal columns. When neuromuscular blockade is used during the initial soft tissue dissection, motor evoked potentials should be assessed after this, but before spinal instrumentation, to determine whether there had been any spinal cord compromise during the initial dissection.