[On the origin of spinal cord potentials evoked by peripheral nerve stimulation and its clinical meaning. Part 1: Clinical study].

In the present paper, the author has attempted to show the origin of the spinal cord potential in man and to establish a practical technique for evaluating the function of the spinal cord and root. In 80 patients with spinal cord and root lesions rectangular current electrical stimulation of 0.1-0.2 msec duration and 1-3 Hz in frequency was given to the median nerve. Basic wave shape of spinal cord potential recorded from epidural space showed the two components which were the biphasic spike wave (the 1st potential) and the negative slow wave (the 2nd potential). The 1st potential elicited by stimulation of the median nerve at the elbow had a duration of 2.3 +/- 0.2 msec and negative peak latency of 7.2 +/- 0.3 msec. The 2nd potential under the same conditions had a duration of 4.1 +/- 1.3 msec and negative peak latency of 9.6 +/- 0.5 msec. The 1st potential elicited by stimulation of the median nerve at the wrist had a duration of 1.9 +/- 0.2 msec and negative peak latency of 10.4 +/- 0.7 msec. The 2nd potential under the same conditions had a duration of 6.2 msec and negative peak latency of 12.2 +/- 0.6 msec. According to the position of leading electrode, the two components changed independently in amplitude. Amplitude of the 2nd potential obtained from the midline of the epidural space was relatively larger than that from facet joints. Evoked spinal cord potentials obtained from the lateral border of facet joints revealed marked 1st potential. Recovery curves of the two components showed that the 1st potential quickly recovered to 100% in amplitude in 10 msec, but that the 2nd potential recovered slowly to only 70% in 100 msec. In cases of root lesions, spinal cord potentials revealed positivity of the 1st potential, polyphasic wave or disappearance of wave shape. In cases of spinal cord lesion, normal 1st potentials and flattening of the 2nd potentials were seen. The author has confirmed that the origin of the 1st potential in man is in primary afferent fiber and that the 2nd potentials in man reflect activity of spinal cord and are excited by synaptic relay. It is highly possible that the cervical root lesion can be differentiated from spinal cord lesion by this method.