413 - Assessing Neuromuscular Asymmetry After Cervical Spinal Cord Injury: A Retrospective Electrophysiological Study

Neuromuscular asymmetry, where one limb exhibits greater muscle strength than the other, is often observed in spinal sord injuries (SCI) subjects, but the etiology and prevalence are rarely studied. The primary objectives of this study were to assess side-to-side differences in limb strength and compound muscle action potentials (CMAPs), and evaluate the etiology of asymmetric weakness.

Design:

This was a retrospective observational study of individuals with complete and incomplete C1-T1 SCI.  The evaluated outcomes were (1) CMAP data of hand muscles, (2) upper extremity muscle strength data based on key muscles in the International Standard for Neurological Classifications of SCI scores and (3) clinical electrodiagnostic (EMG) evaluations.

Results: Sixty-two subjects (9 female, 53 male, age range (14-75)) were evaluated, of which 48 subject had upper extremity EMG study results, 38 individuals had bilateral EMG results available. Of the 48 subjects with EMG results, 7 had acute injuries ( < 6 weeks), 26 had subacute injuries ( > 6 weeks, < 1 year) and 15 had chronic injuries (≥1 year). Significant asymmetry in muscle strength was observed (p < 0.001) across all levels (C5-T1). On average, there was a difference in muscle strength of 1 grade from side to side. A third (31.5%) of individuals with bilateral EMG results had side to side CMAP differences greater than 50%. Common electrodiagnostic findings included intraspinal lesions and peripheral mononeuropathies (53%). Notably, 33% of intraspinal lesions were asymmetric. 

Conclusions: This study reveals significant neuromuscular asymmetry in cervical SCI subjects, with notable differences in muscle strength and CMAP values. These findings highlight the importance of electrodiagnostic exams to guide personalized treatment strategies and enhance understanding of SCI-related neuromuscular dysfunction.