Origin and clinical significance of subcortical components in short-latency somatosensory evoked potentials in children.

P4 (P14 in adults), N' (N18) and N1' (the negative wave after cortical N1, obtained until late infancy) of short-latency somatosensory evoked potentials (S-SEPs) by median nerve stimulation were studied in 13 selected patients. Of these, 12 patients were suggested to have brain-stem lesions responsible especially for the cardinal symptoms and at the same time showed abnormal S-SEPs characteristically between P3 (P13) and N1 (N20). Another patient showed no cortical response with multilocular cystic encephalopathy. Each wave component could be identified by the same methodology as in controls from neonates to adults. In the normal subject the wave forms of P4 and N' were slightly influenced by sleep level. The abnormal S-SEP findings could be classified by an increase and decrease in the wave amplitudes or by a shortening and prolongation in the peak latencies. Upon these classifications we tried to delineate the pathophysiology underlying abnormalities of S-SEPs between P3 and N1. In addition, a negative wave after N1, compatible with N1', was identified in a case without cortical response. Evidence suggests that the origins of P4 and N' may include not only the lemniscal pathway but partly also the extra-lemniscal synapses in the brain-stem. The neural source of N1' seems to be partly in the subcortical structures. As for the clinical significance of S-SEPs in children, the features of P4 and N' are influenced both by the distribution of the affected lesions and by the underlying pathophysiology.