Two cases of quadriparesis following anterior cervical discectomy, with normal perioperative somatosensory evoked potentials.

Two cases illustrate an uncommon failure of perioperative somatosensory evoked potential (SEP) monitoring to detect iatrogenic lesions causing temporary quadriparesis during straightforward cervical surgery. In both cases, anterior cervical discectomy at one or two levels was undertaken with bone graft and titanium implants, and cortical SEP were monitored to alternate stimulation of the left and right median or ulnar nerves. The SEP showed only minor changes during surgery, not considered pathologically significant, and were normal when recorded postoperatively. Both patients, however, experienced marked postoperative limb weakness or paralysis. Motor evoked potentials (MEP) recorded postoperatively to transcranial magnetic stimulation were absent. The clinical motor deficits resolved over the ensuing months. In spite of the normally low incidence of "false negatives," in these two cases SEP monitoring failed to detect a iatrogenic lesion causing moderate to severe, though temporary, motor impairment. Monitoring of MEP may be considered as an alternative to SEP during anterior cervical procedures, while combined monitoring of SEP and MEP may be the ideal.