Intraoperative Upper Limb SSEP Alert During Lower Cord Surgery: A Diagnostic Challenge with Therapeutic Resolution

Background : Intraoperative neurophysiological monitoring (IONM) plays a pivotal role in spinal dysraphism surgery, enabling real-time surveillance of neural pathway integrity and early detection of reversible insults. While lower cord procedures typically impact caudal pathways, upper limb alerts are rare and diagnostically perplexing. Case Description :We report the case of a 10-year-old child undergoing surgical repair of a lipomyelomeningocele with cord detethering in the prone position. Baseline somatosensory evoked potentials (SSEPs) from both upper and lower limbs were stable following positioning. However, a sudden and severe loss of the left ulnar SSEP was identified approximately 53 minutes after the last confirmed intact signal. During this interval, continuous electrocautery for soft tissue exposureprecluded meaningful SSEP acquisition, obscuring the precise timing of signal change. No surgical manipulation occurred near the cervical spine or brachial plexus level. Intervention and Outcome: Suspecting a positional cause, the left wrist and cubital fossa were cushioned using water-filled gloves, and axillary positioning was adjusted to alleviate potential brachial plexus compression. These measures resulted in an instantaneous and complete recovery of the left ulnar SSEP, with no subsequent neurophysiological alerts or postoperative deficits. Conclusion : This case highlights the importance of considering position-related peripheral nerve compromise when unexpected upper limb SSEP alerts arise during lower spinal procedures. Prompt recognition, vigilant interpretation of neurophysiological data and targeted positional interventions, can reverse insults and prevent iatrogenic neurologic deficits ensuring safe surgical outcomes.