[Somatosensory evoked potential of the lower extremity in the premature neonate]

The morphology of SEP is a good index of cortical maturation. Cerebral SEP is elicited by stimulation of the posterior tibial nerve at 38 wk post-conceptional age in 37 neonates distributed in 3 groups: I = gestational age (GA) at birth less than 31 wk; II = GA 23-36 wk; III = full-term neonates (FTN). A somatosensory response was identified in only 21 cases (56.8%). The presence of SEP in 3 groups, ie I, II, III, was 45.5%, 53.8% and 69.2% respectively. The morphological characteristics studied (latencies, amplitude and rising time) in these neonates were different: the peak latencies of major positive wave (P1) and rising time were not significantly different between I and III. These parameters were statistically different between II and III. SEP development is linked to some morphological factors-height, and growth-but also to the maturation of the central nervous system (myelinisation and central pathway organization). These results indicate that until 38-39 wk post-conceptional age, the maturation of the central somatosensory pathway is variable at different birth periods; this suggest the possible role of extra-uterine factors of in the acceleration of neurological development.