Long-Latency Motor Evoked Potentials During An Intraoperative Sentinel Event
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This case study presents a 69-year old male with spinal cord injuries who underwent surgery to repair a pseudomenigocele. During surgery, long-latency motor evoked potentials (LLMEPs) over 100ms were detected in addition to typical short-latency responses under 35ms. LLMEPs disappeared when the patient was positioned prone but returned when reversed to supine. This demonstrates that expanding the recording window to 200ms can reveal LLMEPs, though their clinical utility requires further study. The author encourages documenting and sharing LLMEP findings to advance understanding of this phenomenon.
Long-Latency Motor Evoked Potentials During An Intraoperative Sentinel Event
- 1. Title: Long-Latency Motor Evoked Potentials (LLMEPs): Single-Limb Loss and Return of Motor Evoked Potentials Author: David Barnkow, Au.D., D.ABNM, CCC-A, Medsurant Health, Denver, Colorado The Case Presentation: A 69 year-old male with diagnoses of C3 incomplete tetraplegia, S/P spinal cord untethering, lower extremity central neuropathic pain and pseudomenigocele presented with complaints of progressive weakness, increased spasticity, and emerged upper extremity neuropathic pain. The surgical treatment was posterior cervical exploration and repair pseudomenigocele. Table 1. Motor Strength Assessment Figure 1. Sensory Assessment Pin Prick Figure 2. Right APB TceMEP while supine on bed prior to positioning. Note the presence of complex, large-amplitude response at 103 ms in addition to the anticipated biphasic, low-amplitude response at 35 ms. Figure 4. Right APB TceMEPs while patient returned to supine on bed and anesthesia reversed. Note the LLMEPs return prior to TceMEPs Discussion: SSEPs from the upper and lower extremities remained within acceptable limits throughout this procedure. TceMEPs from bilateral lower extremities and the left upper extremity remained within acceptable limits throughout the procedure. This case study demonstrates that expanding the recording window of current standard TceMEP protocols to 200 ms can reveal another category of motor evoked potentials, the LLMEP. While the underlying mechanisms and clinical utility of LLMEPs have not been described, this author encourages all clinicians to consider expanding their recording window to collect possible LLMEPs, and to publish and share their LLMEP findings for a greater meta-analysis of this interesting, yet essentially undescribed, phenomenon. Figure 3. Right APB TceMEP after positioned prone on OR table and prior to incision. Surgeon was alerted and interventions failed to restore the response. Figure 5. Right APB TceMEP while patient in left lateral decubitus position on operating table. Pre-incision (11:33), Post-incision (13:02) and Closing (13:29). Figure 2. Lateral MRI