INTRAOPERATIVE IMPROVEMENTS OF SOMATOSENSORY-EVOKED POTENTIALS - CORRELATION TO CLINICAL OUTCOME IN SURGERY FOR CERVICAL SPONDYLITIC MYELOPATHY

Study Design. Retrospective review of all patients who underwent surgi cal treatment of cervical spondylitic myelopathy and were monitored by somatosensory evoked potentials. Objectives. To identify the patients who had recognizable improvements in somatosensory evoked potential s ignals intraoperatively and to correlate the changes in somatosensory evoked potential signals to the post-operative clinical status of the patients and compare this group of patients with those that had stable intraoperative somatosensory evoked potential recordings. Summary of Background Data. Somatosensory evoked potentials are commonly used in the operating room to monitor potential injury to the spinal cord or a lterations in spinal cord function. It may be possible to use intraope rative somatosensory evoked potentials to detect improvement in spinal cord function during the decompression of neural structures, as evide nced by an increase in amplitude or a decrease in the latency of the w ave form. Methods. Thirty-two patients with moderate to severe cervica l spondylitic myelopathy requiring multilevel anterior decompression a nd fusion were monitored intraoperatively with somatosensory evoked po tentials. The median and posterior tibial nerves were stimulated at th e wrist and ankle, respectively. Somatosensory evoked potential record ings were obtained from cervical and scalp electrodes by the Nicolet P athfinder electrodiagnostic system, preoperatively, intraoperatively, and postoperatively. Results. Eleven of thirty-two patients demonstrat ed intraoperative improvement of somatosensory evoked potential signal s after decompression. All patients had rapid recovery of motor streng th, bladder control, and ambulatory capacity within days of surgery. T he remaining twenty-one patients had stable somatosensory evoked poten tial recordings. Five had rapid resolution of their symptoms, 15 impro ved over the course of 6 to 8 weeks, and 1 did not improve. The motor recovery of this group at 8 weeks was equal to the group of patients t hat showed intraoperative improvements of evoked potential signals. Co nclusions. 1) Multilevel anterior cervical decompression and fusion pr oduced a significant improvement in the motor function of patients wit h cervical spondylitic myelopathy. 2) Patients with intraoperative inc rease in amplitude or shortening of latency had a more rapid clinical improvement than patients with stable recordings. 3) Long-term reasses sment did not show any difference between patients with intraoperative somatosensory evoked potential improvement-and those with stable soma tosensory evoked potential recordings. Therefore, somatosensory evoked potential improvements cannot be used to determine prognosis at the p resent time. 4) A greater number of patients should be studied using m ore objective methods for quantifying gait patterns and motor function .