Ulnar compound muscle action potentials predict hand muscle strength 1 year after cervical spinal cord injury: A...

Lower motor neuron (LMN) dysfunction caused by anterior horn cell damage in the ventral gray matter during spinal cord injury (SCI) may impact long-term prognosis.

To determine the influence of the 3-month ulnar compound muscle action potentials (CMAP; representative of C8-T1 spinal segmental LMN integrity) on hand muscle strength and function, 12 months following SCI.

We completed retrospective analyses of the European Multicenter Study about SCI (EMSCI) database. Included participants had traumatic SCI (motor complete or incomplete), initial neurological level of injury C1-C8, and ulnar CMAP from the abductor digiti minimi in at least one limb, 3 months after injury. We trichotomized 3-month ulnar CMAP into absent (CMAP = 0.0 mV), reduced (CMAP <6.0 mV), and normal (CMAP ≥6.0 mV), and constructed logistical regression models to predict 12-month C8 and T1 motor scores, dichotomized into poor (≤3) and functional (>3). We explored relationships between trichotomized 3-month ulnar CMAP and 12-month functional Graded Redefined Assessment of Strength, Sensation and Prehension (GRASSP) and Spinal Cord Independence Measure (SCIM) upper limb sub-scales, using non-parametric statistics.

Data from 318 participants (253 males), 46.8 years old (SD 18.4), resulted in CMAP and corresponding motor scores in 629 limbs. Adjusted logistical regression models were significant for C8 and T1 motor scores, with absent (C8 36.6, 95 % CI 12.9-133; T1 38.7, 95 % CI 11.2-24) and reduced (C8 11.0, 95 % CI 6.7-18.4; T1 7.93, 95 % CI 5.2-12.3) CMAP, predictive of poor 12-month motor scores. 12-month GRASSP (n = 30) and SCIM scores were significantly higher in those with normal 3-month ulnar CMAPs than absent and reduced.

There is a 7 to 38-fold higher likelihood that SCI individuals with reduced or absent 3-month ulnar CMAP will demonstrate poor hand motor scores at 12 months. This aligns with significantly worse GRASSP and SCIM functional scores. Our findings justify adding LMN health measures in prognostic modeling after SCI.