Trans-spinal myogenic evoked potentials: a novel intraoperative technique for localizing motor deficits following loss of transcranial motor evoked potentials.

Trans-spinal motor evoked potentials (TsMEP) represent a novel intraoperative neuromonitoring technique designed to localize motor deficits when transcranial motor evoked potentials (TcMEP) are lost or unreliable. This technique involves direct electrical stimulation of the spinal cord through pedicle screws using a train of biphasic square-wave pulses, with myogenic responses recorded from limb muscles. In the presented case of kyphoscoliosis correction, TsMEP was employed after TcMEP signals failed to recover despite corrective measures. Stimulation at various vertebral levels allowed TsMEP to localize the level of motor pathway compromise, guiding targeted decompression. Unlike sensory-based methods such as dynamic spinal cord mapping, TsMEP directly evaluates motor tract integrity and provides real-time, segmental information without the need for epidural instrumentation. This technique also enabled monitoring of functional recovery through threshold changes, demonstrating its clinical utility. TsMEP holds promise as an intraoperative diagnostic and decision-making tool, especially in complex spinal surgeries with high neurological risk.