Short- and long-latency median somatosensory evoked potentials. Findings in patients with localized neurological lesions.

Short- and long-latency somatosensory evoked potentials (SEPs) were elicited by stimulation of the median nerve in 43 patients with neurological disorders. Abnormalities of short-latency peaks, P9, N13, and P14, were seen in patients with lesions of the peripheral nerve, cervical spinal cord, and brain stem, respectively. Subsequent component, N18, was affected in patients with thalamic or hemispheric disease. In some patients with parietal lobe lesions, however, abnormalities were limited to later components, N32 or N63. Analysis of SEPs is helpful in localizing a lesion along the somatosensory pathway, although differentiation between thalamic and other subcortical or cortical involvement may not be possible with the present SEP technique. Both short- and long-latency SEPs should be studied for maximal clinical information. The latter can be most reliably evaluated by simultaneous bilateral stimulation.