Dermatomal somatosensory evoked potentials in the diagnosis of lumbosacral spinal stenosis: comparison with imaging studies.

Dermatomal somatosensory evoked potentials (DSEPs) and computerized tomography/magnetic resonance (CT and/or MR) images were retrospectively analyzed to evaluate their relationship in the diagnosis of lumbosacral spinal stenosis (SS). Of 155 patients referred for DSEPs with a clinical suspicion of lumbosacral SS, 58 met the inclusion criteria. DSEP abnormality was defined as: (1) N1 latency absent or greater than 2.5 SD; (2) side-to-side latency difference greater than 2 SD; (3) amplitudes greater than 2 SD below the mean; or (4) amplitude ratio greater than 2 SD. Involvement of two or more DSEP levels by any of the above criteria was labeled multiple root disease (MRD). Involvement of one level was labeled single root disease (SRD). Images were reviewed independently by a neuroradiologist. Results revealed 54 subjects with SS by imaging; 42 had MRD and 8 had SRD by DSEPs. Sensitivity for MRD and SS was 78%, and for MRD plus SRD and SS was 93%.