Somatosensory Evoked Potential Responses in Focal Brain Lesions

ABSTRACT

Cerebral somatosensory evoked potentials(SEPs) produced by stimulation of peripheral nerves provide a useful diagnostic index of conduction in somatosensory pathways to the cortex. Thus the integrity of both the dorsal column-medial lemniscus pathway and primary sensorimotor area has been considered an essential requirement to record a normal SEP. There are suggestions that SEPs contain several components arising from different neuronal sources, the early short latency potentials corresponding to the lemniscus-mediated responses and the late waves to the diffuse spino-thalamic projections. The present work analyses the influence on SEPs of focal brain lesions, using the computerized tomography in detecting and localizing brain lesions. Somatosensory evoked potentials were recorded in 20 patients with focal brain lesions recognized by computerized tomography. 1) Patients with primary sensorimotor area(PSMA) damages(group I) had a very abnormal of the early component(No, Po, Nl, Pl) in 100% on the lesion side. 2) Patients presented supratentorial lesions, sparing PSMA(group II), 87.5% showing abnormal SEPs in early components and characterized by increment of amplitude in late components. 3) Brainstem damage(group III) produced a distortion of the early components especially N11, N20msec in latency. 4) In incomplete spinal cord injuries, the SEPs is indeed signal of functional recovery, of posterior column, and incorrespondance with clinical improvement.