Imaging Predictors for Significant Lower Motor Neuron Injury in Traumatic Cervical Spinal Cord Injury

INTRODUCTION Traumatic spinal cord injury (SCI) results in loss of both white and grey matter in the spinal cord and adjacent to the site of impact. Loss of gray matter within the injured area leads to lower motor neuron (LMN) injury, due to direct destruction of the alpha motor neurons and associated axonal loss within the adjacent peripheral nerves. The extent of gray matter loss can be discrete, or it can extend multiple levels from the site of impact. Since these changes can become irreversible within a year after injury, early identification of significant LMN injury in patients with traumatic SCI allows them to benefit from available reconstructive surgeries before the window for reinnervation closes. METHODS In this single-center retrospective study the charts of 21 previously healthy individuals aged 15 to 50 yr who suffered traumatic SCI with AIS C4-C8 A-D classification and hand functional impairment, without concomitant peripheral nerve or brachial plexus injury, were reviewed. Magnetic resonance (MR) images of cervical spine, obtained within 6 wk from the injury, were reviewed to identify structural imaging characteristics that correspond to gray matter destruction. Severity of LMN injury predicted by imaging findings was compared with the results of compound muscle action potential (CMAP), motor unit potential (MUP), intraoperative stimulation, and Medical Research Council (MRC) grading of the major muscle groups of the upper extremity. RESULTS The extent of LMN injury as determined by electrophysiological evaluations and intraoperative stimulation could be predicted with some degree of specificity by the preoperative imaging findings. CONCLUSION In this study, simple imaging biomarkers indicate the extent of LMN injury in patients with traumatic SCI. By noting the extent of soft tissue damage within the injured metamere of the spinal cord, the degree of lower motor neuron injury can be anticipated and thus appropriate triage performed.