Functional evaluation using several evoked spinal cord potentials in elderly patients with cervical spondylotic myelopathy

摘要

BACKGROUND: The recordings of evoked spinal cord potentials following epidural spinal cord stimulation are thought to be generated by volleys traversing the dorsal column pathway, and it may not directly reflect conduction defects in corticospinal tracts of cervical spinal cord. To our knowledge there has been few report using several evoked spinal cord potentials in function evaluation of the cervical spinal cord in elderly patients with cervical spondylotic myelopathy (CSM). OBJECTIVE: To investigate the function states of the cervical spinal cord in elderly patients with CSM and explore its pathophysiologic mechanism. DESIGN: Case observation. SETTING: Department of Orthopedics for the aged, Shenzhen Pingle Hospital of Orthopedics. Department of Orthopedic Surgery, Yamaguchi University School of Medicine. PARTICIPANTS: A total of 23 elderly patients with CSM who received treatment in the Department of Orthopedic Surgery, Yamaguchi University School of Medicine of Japan from January 2003 to February 2004 were enrolled in this study. Inclusive criteria: ① Multiple intervertebral levels of cervical spinal cord compression confirmed by MRI, e.g. 3 or more than 3 levels of compressin. ② Age ≥70 years old. ③ Numbness and sensory disturbance in the upper limbs and showed hyperreflexia in the lower limbs. Exclusive criteria: Patients with abnormal motor and sensory nerve conduction velocities in both upper and lower limbs were excluded. METHODS: Evoked spinal cord potentials (ESCPs) following transcranial electric stimulation (TCE-ESCPs), epidural spinal cord stimulation (Spinal-ESCPs) and median nerve stimulation (MN-ESCPs) were recorded in 23 patients from posterior epidural space intraoperatively. The abnormalities of TCE-ESCPs were defined as attenuation of amplitude of the D wave. The most cranial intervertebral level showing abnormal TCE-ESCPs with a marked reduction in size of the negative peak (reduction of over 50%) was considered as the upper level of the spinal cord lesion with respect to the corticospinal tract in white matter. The abnormalities of Spinal-ESCPs were defined as marked reduction in the size of negative peak (reduction of over 50%). The most caudal intervertebral level showing abnormal Spinal-ESCPs was considered as the lower level of the spinal cord lesion with respect to the dorsal column pathway in white matter. The abnormalities of MN-ESCPs were defined as attenuation of the N13 amplitude,which was considered as the lesion level of the spinal cord with respect to the dorsal horn in gray matter. Radiological investigation: Lateral view of plain X-ray films was obtained in flexion and extension of the cervical spine. Instability of the cervical intervertebral level was determined as horizontal displacement of the vertebral body of over 3 mm. MAIN OUTCOME MEASURES: The results of examination of TCE-ESCPs, Spinal-ESCPs and MN-ESCPs in elderly patients with CSM. RESULTS: The 23 elderly patients with CSM were participated in the result analysis. ①TCE-ESCPs: The impairment of the corticospinal tract in white matter at single intervertebral level was revealed in 18 of 23 patients by recordings of TCE-ESCPs (sensitivity 78%). In the 18 patients, the lesion level was shown at the upper cervical segment in 14 patients (C3-4 n=10 and C4-5 n=4), and at the lower cervical segment in 4 patients (C5-6 n=4). ②Spinal-ESCPs: The impairment of the dorsal column pathway of white matter at single intervertebral level was revealed in 17 of 23 patients, by recordings of Spinal-ESCPs (sensitivity 74%). In the 17 patients, the lesion level was presented at the upper cervical segment in 14 patients (C3-4 n=10 and C4-5 n=4), and at the lower cervical segment in 3 patients (C5-6 n=3). ③MN-ESCPs: All patients revealed abnormal MN-ESCPs at one or more intervertebral levels (sensitivity 100%). The impairment at single intervertebral level was demonstrated in 17 patients, and the impairment at multiple intervertebral levels was shown in 4 patients (3 patients at the C3-4, C4-5, and C5-6, and one patient at the C4-5, C5-6, and C6-7). ④Radiological findings: The Instability of the intervertebral level at the C3-4 or C4-5 motion segment was seen in 15 patients, with a total of 20 levels, and where 10 were at the C3-4 intervertebral level and 5 were at the C3-4, C4-5 intervertebral level. CONCLUSION: The results suggest that in most elderly patients with CSM who have multiple intervertebral level compressions of the cervical spinal cord on MRI, white matter is impaired at the single cervical intervertebral level, and not only the dorsal column pathway, but also the corticospinal tract can be affected. Combined the findings of radiography, the excessive motion and instability of the C3-4 or C4-5 intervertebral level plays an important role in inducing the long tract lesion in elderly patients with CSM.