[Dermatomal somatosensory evoked potentials from L3, L4, L5 and S1 spinal roots in healthy subjects]

Dermatomal somatosensory evoked potentials (DSEPs) were recorded in 62 healthy volunteers aged from 15 to 65 years (mean 36.8 +/- 12.9 years) with height from 1.5 to 1.92m (mean 1.69 +/- 0.10m). The aim of the study was to establish normal values for L3, L4, L5 and S1 dermatomes and to introduce this method for the neurophysiological diagnosis of chronic lumbosacral pain and disc disease. The signature areas of dermatomes in both legs separately were stimulated according to the method described by Sedgwick and Katifi (1985). DSEPs were recorded from the scalp electrodes placed at Cz', referred to Fpz. The latencies and amplitudes of consecutive components of DSEPs: N33, P40, N50, P60, N75 and side to side differences were measured and evaluated. Statistical analysis of the results revealed significant positive correlation of DSEPs latencies as a function of height. The correlation of amplitudes with height was less significant. Age, on other hand, showed only negative correlation with amplitudes of later DSEP components. On the basis of the performed analysis the latency of P40 and amplitude of P40-N50 seem to be the best parameters for the evaluation of pathological DSEPs. The range of normal value of latencies for stimulated roots should be calculated from regression equation with the subject's height. As regards amplitude, side to side mean value difference above two standard deviation appears to be more useful.