S113. Intraoperative recording of somatosensory evoked potentials from both peripheral median nerve and proximal upper trunk to assess C5, C6 brachial plexus injury

Introduction The prognosis of reconstructive surgery for brachial plexus injuries is related to the localisation of injury, whether the damage exists primarily in the brachial plexus, the spinal nerves distal to the dorsal root ganglia, or at the point of connection with the spinal cord (Jones, 1980). The use of somatosensory evoked potentials (SSEP) to monitor upper extremity nerves during surgery is becoming more accepted as a valid and useful technique to minimize intraoperative nerve injuries (Son et al., 2017). When SEP recording is used in an operating theater, it is valuable for evaluating proximal root lesions (Sugioka, 1984). We present a case illustrating the benefit of utilizing both SSEP from peripheral median nerve (MN) and from brachial plexus lateral cord (LC) and upper trunk (UT) for conducting the surgery procedure. Neurosurgeons decided to do nerve transfer, distal spinal accessory nerve to suprascapular nerve and ulnar nerve branch to musculocutaneous (MC) nerve, as it was found that the lesion might correspond to C5, C6 roots avulsion instead of nerve graft for the initially suspected lateral cord injury. Methods EMG test before surgery and intraoperative muscle MEP mapping technique and SSEP from MN, LC, anterior division of the upper trunk (ADUT) and UT in a 66-year-old patient with total left forearm flexion and shoulder abduction paralysis after motorbike accident occurred 4 months earlier. SSEP protocols (4.1 Hz stimulus rate and 300 sweeps) were already installed in the IONM NIM-eclipse Medtronic device. We used subdermal paired electrodes for MN stimulation and two hooked monopolar electrodes for proximal stimulation (LC, ADUT and UT). The peripheral nerve distal SSEP and proximal brachial plexus SSEP were recorded from spinal Cs2-Fpz, inion-Fpz and C4’-Fpz channels. For muscle MEP and raw EMG were used paired subdermal electrodes in deltoid, biceps, EDC, APB and ADM muscles. Results EMG: 3 weeks after the accident and 4 days before surgery showed acute denervation in myotomes corresponding to C5, C6 root levels. SNAP of ulnar, median and radial nerves were present. Intraoperatively, muscle MEP did not show responses from LC to biceps and from posterior cord to deltoid muscle. SSEP from MN showed delayed N13 at 23 ms and P(N)20 at 27 ms. SSEP from LC showed N13 at 15 ms and P20 at 20 ms. From ADUT and from the UT SSEP was obtained at cervical level but not from the cortex. At this moment we added another channel Fpz-inion. The UT SSEP was absent in inion-Fpz, C4‘-Fpz while peripheral MN SSEP showed responses at three C2 spinal, inion and cortex levels. Conclusion We proved the sensory-motor dysfunction of the ADUT, UT and proximally to the site of connection with the spinal cord, both with muscle MEP mapping and SSEP absence (ADUT and UT) at cortical level and neurosurgeons decided to perform a nerve transfer instead of a nerve graft. This report demonstrates a case in which IONM was useful in identifying the lesion site during brachial plexus surgery.