Prognostic value of somatosensory-evoked potentials in the surgical management of cervical spondylotic myelopathy

Study Design. Preoperative somatosensory-evoked potentials (SEPs) were retrospectively analyzed and classified, and compared with surgical outcome. Objective. To evaluate the value of the preoperative SEP waveform in predicting the clinical outcome after surgical management of cervical spondylotic myelopathy (CSM). Summary of Background Data. SEPs have played an important role in spinal surgery. However, the value of SEPs in predicting the outcome of surgery for CSM remains controversial. Methods. This study enrolled 76 CSM patients who underwent surgical intervention. Median nerve SEPs were recorded before surgery. The Japanese Orthopedic Association (JOA) scoring system was used to evaluate the neurologic function before surgery and at postoperative follow-up at 1, 3, 6, 12, and 24 months. Patients were divided into 5 groups according to the classification of their preoperative SEP waveforms. Group I patients had normal SEPs, group IIa had normal latency and abnormal amplitude, group IIb had abnormal latency and normal amplitude, group III had abnormal latency and amplitude, and group IV had immeasurable waveforms. The myelopathic disability scores and surgical outcomes in different groups were compared by the Kruskal-Wallis test. Results. The SEP classification was found to be significantly associated with the JOA score (Pearson's chi(2) test, chi(2) = 53.9, P < 0.05). There were no significant differences in JOA score recovery at different follow-up times within any SEP group. At 24 months after surgery, there was no significant difference in the recovery ratio between groups I and IIa, or between groups IIb and III (Kruskal-Wallis test, P > 0.05). However, the recovery ratio was significantly higher in groups I and IIa than in all the other groups (Kruskal-Wallis test, P < 0.05), and in groups IIb and III than in group IV (Kruskal-Wallis test, P < 0.05). Conclusion. SEP classification correlates well with CSM disability and postoperative recovery ratio. Median nerve SEP recordings would be a valuable and practical tool for the diagnosis and prognosis of myelopathy.