On the usefulness of somatosensory evoked responses for the evaluation of lower back pain.

Electrodiagnostic and concurrent computed tomographic (CT) scan data were reviewed from 30 patients with lower back pain and unilateral radicular symptoms. Electrodiagnostic examination included somatosensory evoked responses (SSEPs) of the L-4, L-5, and S-1 roots stimulating specific sensory nerves. In three patients with normal CT scans, electrophysiologic studies were unrevealing. In the remaining 27 patients, CT scans were consistent with root injury, as were 15 of 17 myelograms. In 21 of these 27 patients, SSEP abnormalities consistent with focal root dysfunction and the radiographic findings were present. Other electrodiagnostic abnormalities (ie, electromyographic F response or H reflex) were limited to the six patients with clinical signs. These data indicate that SSEPs are valuable for evaluating root injury in patients with lower back pain, particularly where focal sensorimotor or reflex signs are absent.