The clinical use of dermatomal somatosensory evoked potentials in lumbosacral spinal stenosis.

DSEPs provide clinicians with a safe, noninvasive technique useful in determining which patients with anatomic spinal stenosis have the added component of neurogenic compromise. Based on physiologic principles, level-by-level prolongation of DSEP latencies, reduction of amplitude, asymmetry, or a complete absence of response is associated with dysfunction in that particular afferent neurologic pathway. This dysfunction does not correspond to the exact level of stenosis noted on MRI because the rootlets in the lumbar and sacral regions pass through multiple spinal segments as they course rostrally through the spinal canal. Given that LSSS typically develops over time, the degree of abnormality likely would correspond to the physiologic slowing occurring in the multiple rootlets of the cauda equina. These recordings are not easy to perform and interpret, but when done correctly, they provide the best evidence for the type of neurophysiologic dysfunction in LSSS that responds favorably to surgical decompression. Similarly, DSEPs might provide a means of neurophysiologically monitoring clinically significant findings in a program of conservative management.