Clinical value of motor evoked potentials with transcranial magnetic stimulation in the assessment of lumbar spinal stenosis

The objective of this study was to evaluate the clinical usefulness of assessing motor evoked potentials (MEP) in lumbar spinal stenosis (LSS). Twenty-three LSS patients were enrolled. The preoperative data of MEP latency (MEPLT), clinical symptoms, Japanese Orthopaedic Association (JOA) scores for low back pain, visual analogue scale (VAS) for back pain, leg pain and numbness, walking distance and the minimal cross-sectional area (mCSA) of the dural sac were evaluated. The mean MEPLT was 42.1 +/- 2.8 ms. Fourteen patients had bilateral leg symptoms. The mean walking distance and mCSA were 302.1 +/- 302.8 m and 0.4 +/- 0.2 cm(2), respectively. The mean JOA score and VAS scores for back pain, leg pain and numbness were 15.9 +/- 4.8, 6.0 +/- 2.9, 7.7 +/- 1.9 and 7.3 +/- 3.0, respectively. MEPLT was related to the walking distance, limb symptoms and the VAS for numbness. MEPLT was significantly delayed in patients who showed a walking distance less than 500 m. MEP is useful in LSS assessment. It can reflect the subjective severity of motor disturbance and predict the neurological deficit prior to appearance.