Somatosensory evoked potentials. Diagnostic criteria and abnormalities in cerebral lesions.

In order to advance the practical application of measuring evoked cortical responses following electrical stimulation of the median nerve at the wrist (SEP) in clinical neurology, diagnostic criteria, consisting of the onset latency, peak latency and 2 indices of the first 3 negative components, and their left-and-right differences, were proposed and applied to 65 patients with cerebral lesions of various aetiologies. The criteria used were shown to be very useful in distinguishing between normal subjects and patients with cerebral lesions. The N1 and N2 components were related to the involvement of sensory pathways and were commonly associated with sensory impairment of all modalities or of deep proprioceptive and cortical modalities. The N3 component, on the other hand, was related to the presence of lesions and non-specific sites as well as non-specific symptomatology. SEP, judged by the present criteria, was shown to be useful as a complementary diagnostic aid in localizing the sites of lesions in sensory pathways and in evaluating sensory function, especially when used in combination with clinical symptomatology.