Somatosensory evoked potentials (SSEP)study is a simple and quantitative test, and has been used to evaluate the sensory system along the somatosensory pathway from peripheral sensory receptor to the cortex. The ascending pathway of SSEP had been
known
to be posterior column-lemniscal pathway, but not without controversy. To define the relationship between SSEPs and sensory changes. The posterior tibial SSEPs of 226 extremities with variable inds of myelopathy were analyzed and compared with
123
healthy adults without definite neurological deficit. The legs of myelopathy were divided into 4 groups; A group, 58 extremities showing lateral column dysfunction; B group 45 extremities showing posterior columhn dysfunction ; C group, 109
extremities
showing both sateral and posterior column dysfunction ; D group, 14 extremities showing no definite sensory deficit. Following results are obtained :1. Spinal T12 evoked potentials are detected in all normal control and patients with myelopathy.
Cortical P1 evoked potentials, however, are detectable in 59-100% of patients depending on sensory deficits, especially low in the groups of posterior column dysfunction(59-86%0. 2. There is no significant difference in latencles and amplitudes
of
spinal T 12 between normal controls and patients with myelopathy. 3. The mean latency of cortical P1 and central conduction time (CCT) of the patients with myelopathy are significantly prolonged compared to the group with normal
control(p<0.05)and
the
amplitudes are also significantly diminished(<0.05). 4. The changes on latencies and amplitudes of cortical P1 are correlated to the integrity of posterior column rather than to that of the lateral column.
In conclusion, this stucy shows that the main conduction pathway of SSEP is the posterior column rather than lateral column and, that SSEP is a clinically valuable noninvasive tool for evaluating posterior column function objectively and
quantitatively.
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