| Abstract: | BACKGROUND: Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) can display the site of lumbar spinal stenosis and predict nervous compression at the morphological level; however, pure morphological changes cannot reflect functional alterations in a compressed nerve root. Dermatomal somatosensory evoked potential (DSEP) provides a means to assess the functional state of a nerve root. OBJECTIVE: To evaluate the clinical significance of DSEP, assessing the degree of nerve root injury following lumbar spinal stenosis. DESIGN, TIME AND SETTING: A case-control study was performed in the Department of Orthopaedic Surgery, Hainan People's Hospital, China, between September 2004 and December 2007. PARTICIPANTS: Forty-seven patients diagnosed with lumbar spinal stenosis by CT or MRI were selected as the case group; fifty healthy subjects were collected as the control group. METHODS: A KEYPOINT myoelectric evoked potential apparatus (DANTEC Company, Denmark) was used to measure DSEP, and stimulative spots were determined in accordance with the skin key sensory spot standards established by The American Spinal Injury Association: L4 in the medial malleolus, L5 in the third metatarsophalangeal joint of the dorsum of foot and S1 in the lateral heel. The needle electrode used as the recording electrode was located at the Cz point of the cranium, and the reference electrode at the Fz point. MAIN OUTCOME MEASURES: Latency of the P40 peak of DSEE P1-N1 amplitude, P40 waveform and differentiation and disappearance of various waves. RESULTS: The sensitivity and diagnostic concurrence with surgery of nerve root injury following lumbar spinal stenosis evaluated by DSEP was 95.7 %. P40 latencies at L4, L5 and S1 in the case group were significantly longer than in the control group (P < 0.05), and the P1-N1 amplitude in the case group was significantly lower than the control group (P < 0.05-0.01). Nerve root injury was categorized according to DSEP latency as follows: severe damage (disappearance of the P40 wave in 103 dermatomes), moderate damage (prolongation of the P40 peak latency ≥ 3.0 times the standard deviation of the normal mean in 60 dermatomes) and mild damage (prolongation of the P40 peak latency ≥ 2.5 times the standard deviation of the normal mean in 31 dermatomes).CONCLUSION: DSEP can be used to determine the severity of nerve root injury following lumbar spinal stenosis with high sensitivity and specificity. |
