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The purpose of this study was to examine the clinical value of S-SEP (short latency somatosensory evoked potentials) as a routine test of spinal cord function. On the basis of a preliminary study determining the optimal recording conditions in normal individuals, S-SEP measurement was carried out in patients with cervical myelopathy to examine its diagnostic value for spinal cord lesions. In these patients, the best recordings of N9, N11, and N13 were obtained from the cervical spinous processes with linked ear reference (A1 + A2). In severe myelopathy, the N11-N13 interpeak latency was prolonged. Those with impaired bladder function or decreased deep sensation showed a prolonged N9-N13 interpeak latency. In cases of C3-4 and C4-5 lesions, the N9-N13 and N9-P14 interpeak latencies were significantly more prolonged than in those with C5-6 lesions. The interpeak latencies from P14 to N9 and N11 gradually became shorter postoperatively.

The ESCPs (evoked spinal cord potentials) resulting from both median nerve and spinal cord stimulation were recorded from the interlaminar yellow ligaments posteriorly or intervertebral discs anteriorly on patients with cervical myelopathy in order to determine the most significant lesion in the spinal cord electrophysiologically. The normal median-nerve-evoked spinal cord potential (MN-ESCP) consisted of P1N1 and N2(P2) deflections, while normal spinal cord-ascending evoked spinal cord potential (SC-AESCP) consisted of N1 and N2 deflections. The abnormal ESCPs obtained from 65 patients were classified into three grades. The spinal level recording the highest grade of ESCP, which was mostly positive wave, generally corresponded to the level that was clearly diagnosed as the main lesion by neurologic and radiologic examinations, such as a case of single level disc hernia. With these techniques, the level diagnostic rates of primary lesions were 94.7% in posterior recordings and 74.1% in anterior recordings.