Evaluation of cervical cord function using spinal evoked potentials from surface electrode.

Spinal evoked potentials from cervical skin surface (surface spinal evoked potentials) were measured to evaluate spinal cord function as a convenient method that precludes inserting electrodes into the epidural space, and results were compared with those of the former epidural recording method. Surface spinal evoked potentials were obtained from cervical skin surface over the C3, C5, and C7 spinous processes after median nerve stimulation in 18 normal subjects and 37 patients with a cervical lesion. In normal subjects, surface spinal evoked potentials consisted of three negative waves (N1, N2, N3). Abnormal N2 (80%) and abnormal N3 (100%) were observed in cervical myelopathy, and abnormal N2 was observed only in radiculopathy; this allows for differentiation between myelopathy and radiculopathy. Comparing preoperative and postoperative surface spinal evoked potentials, it was seen that improvement of clinical symptoms was proportional to that of surface spinal evoked potentials.