Intraoperative Neurophysiologic Monitoring With Hoffman Reflex During Thoracic Spine Surgery: A Lesson From A Series Of 18 Patients (P5.101)

OBJECTIVE: The purpose of this study is to examine the role of H-reflex in identifying intraoperative spinal cord injury and predicting postoperative neurological outcomes in patients undergoing thoracic spine surgery. BACKGROUND: Introperative somatosensory evoked potentials (SSEPs) and transcranial motor evoked potentials are widely used in a variety of spinal surgeries to reduce the risk of spinal cord injury. However, in several animal studies the H-reflex has been shown to have greater sensitivity in detecting thoracic spinal cord ischemia. DESIGN/METHODS: We retrospectively reviewed 18 cases that underwent thoracic spine surgery for metastatic thoracic spinal tumors between 2011 and 2012 at the MD Anderson Cancer center. Demographic and surgical information, intraoperative neurophysiologic changes, and pre- and postoperative (at three and six months) neurologic status were collected. RESULTS: To monitor spinal cord function, H-waves and SSEPs were simultaneously monitored in our series, consisting of 4 female and 14 male patients aged 10-71 years. In 8/18 cases, metastatic tumors involved T1-6 spinal levels, while 10/18 cases had T7-12 spinal level involvement. The average intraoperative neurophysiologic monitoring (IONM) time was 5 hours (range: 3-12 hours). Surgeries were carried out under standard general anesthesia with continuous IONM. In 13/18 cases, bilateral H-waves and SSEPs were stable throughout IONM. 4/18 cases had a <50% transient reduction in H-wave amplitude that later returned to baseline. In 1/18 case, SSEPs were absent from baseline throughout surgery. In our cohort, neither general anesthesia nor low dose muscle relaxants interfered with the H-waves. Pre-operatively, our series had Karnofsky performance status score of at least 90 with no significant lower extremity weakness. At three and six months follow up, none of the patients exhibited new post-operative neurological deficits. CONCLUSIONS: Stable intraoperative H-waves and SSEPs are suggestive of preserved postoperative neurologic outcomes. Given its greater sensitivity to spinal cord ischemia, relatively low cost, and ease of acquisition, H-reflex monitoring could be a useful adjunctive during thoracic spine surgeries. Study Supported by: Disclosure: Dr. Feyissa has nothing to disclose. Dr. Smith has nothing to disclose. Dr. Tummala has nothing to disclose.