The diagnostic utility of dermatomal evoked potentials.

A study was completed to evaluate the diagnostic utility of dermatomal evoked potentials (EPs) for identifying single and multiple sensory nerve root compromise. We examined the clinical records of 37 patients referred for neck and lower back pain with particular attention paid to presenting clinical symptoms, magnetic resonance (MR) imaging results, and cervical and/or lumbar dermatomal EP results. The primary object of this study was to determine whether or not dermatomal EPs provided useful diagnostic information about nerve root function that would supplement the structural information provided by the MR imaging. We evaluated an outpatient population presenting with neck and lower back pain. These patients had detailed clinical evaluations, MR images, and EP evaluations, each done by independent sources. EP studies included mixed nerve EPs (ulnar and median or tibial nerve), and either C6 and C8 or L4, L5, and S1 dermatomal EPs for cervical and lumbar disorders, respectively. Mixed nerve and dermatomal EPs provided reliable information about nerve root function that corresponded to clinical symptoms more closely than did the MR findings. Specifically, these EPs often provided additional information about lateralized nerve root dysfunction beyond that given by the MR imaging. In some cases, EPs identified disturbances in nerve root function in the absence of MR-imaging-identified structural abnormality.