Segmental infralesional lower motor neuron abnormalities in patients with sub-acute traumatic spinal cord injury

The health of the infralesional lower motor neuron (LMN) has received little attention in individuals with traumatic cervical spinal cord injuries (SCI). Infralesional LMN health is clinically relevant in the context of nerve transfer surgery to restore critical upper limb functions, as those demonstrating LMN damage below the neurological level of injury may experience irreversible sequelae of denervation (e.g., atrophy, fibrosis) without timely intervention. In this two-centre retrospective cohort study, we examined the health of the infralesional LMN in individuals with traumatic cervical SCI, using data derived from the clinical electrodiagnostic examination performed early after SCI. We assessed 66 limbs in 42 individuals with traumatic cervical SCI (40 males, mean age = 43.6±17.2, mean duration from injury = 3.3±1.5 months, 25 with motor complete injuries). Analysis was stratified by injury level as 1) C4 and above, 2) C5 and 3) C6-7. EMG performed on representative muscles from C5-6, C6-7, C7-8 and C8-T1, were included in analysis. LMN abnormality was dichotomized as present (abnormal spontaneous activity) or absent. Data were pooled for the most caudal infralesional segment (C8-T1). Overall, a high frequency of denervation potentials was seen in all infralesional segments for all injury levels. The pooled frequency of denervation potentials at C8-T1 was 74.6% of limbs tested. There was also evidence of denervation potentials at the rostral border of the neurological level of injury, as high as 64.3% of C5-6 muscles for C5 injuries. These data support a high prevalence of infralesional LMN abnormality following SCI, which has implications to candidacy, timing of the intervention, donor nerve options and motor prognosis following SCI.