Comparison of the human evoked electrospinogram recorded from the intrathecal, epidural and cutaneous levels

In 30 patients (17 of whom had a clinically normal spinal cord) spinal cord potentials evoked by peripheral nerve stimulation were studied with computer averaging techniques in order to compare the intrathecal, epidural and skin records. In epidural and skin records, segmental spinal cord potentials either recorded from lower cervical or lower thoracic intervertebral levels often had similar shapes and latencies, especially with regard to the first component of the intrathecally recorded responses. The second slow component became less significant and was even absent in some cases. The amplitude of the first component was on average 33% of that recorded intrathecally when recorded epidurally and only 10% when recorded from the skin. In three cases potentials of very prolonged onset latency were recorded epidurally or cutaneously while in the same cases intrathecal records resulted in potentials with normal latencies. Cervical tract responses at the C6--7 intervertebral level after stimulation of the posterior tibial nerve were studied by the 3 recording methods. Epidural and skin records failed to reveal such a response regularly, while intrathecal recording invariably provided the cervical tract response. The 3 recording methods were discussed with respect to clinical applications and research. It can be stated with some reservation that epidural and skin surface recording techniques could be exploited it one could know the time of arrival segmental afferent inputs at the spinal cord.