Somatosensory evoked potentials in the evaluation of lumbosacral radiculopathy.

We performed lower extremity somatosensory evoked potential (SEP) studies in 59 patients with signs or symptoms suggestive of lumbosacral radiculopathy and compared them with results of myelography with post-myelogram CT (myelogram/CT), MRI, and other electrodiagnostic studies. Of 38 patients with abnormal myelogram/CTs, 32 had abnormal SEPs, while 11 demonstrated EMG abnormalities. All 21 patients with normal myelogram/CTs had normal SEPs. SEP improved electrodiagnostic sensitivity in patients with weakness or reflex changes as well as in those with sensory deficits only. SEP was less sensitive in patients in whom spinal stenosis was the only radiographic finding. MRI generally corresponded well with the results of myelogram/CT and SEP but overestimated the significance of disk bulges in some patients. SEP is useful in the electrodiagnostic evaluation of lumbosacral radiculopathy, particularly when EMG is nondiagnostic.