Diagnostic significance of tibial nerve somatosensory evoked potentials (spinal and cortical components) with spinal cord lesions.

Forty normal subjects were investigated with the somatosensory evoked potential technique following stimulation of the posterior tibial nerve in order to yield information upon normal values, and especially the origin of the cervical potential. Subsequently an electrophysiologic localization of tumours along the spinal cord was attempted in 18 patients with spinal tumours. In C2 recordings with Fz reference 3 components, N28, N30, and N34, are visible. Simultaneous cortical and cervical recordings with mastoid, knee, and neck references suggest a cranio-cervical origin of N28, a subcortical origin of N30 and a thalamic or thalamo-cortical origin of N34. In patients, the lumbar spinal cord potentials regularly yielded a useful additional information with respect to the tumour site. The cervical potentials added in 5 out of 18 patients additional information localizing the tumour within the spinal cord or brain-stem.