Quantitative electrophysiological assessments as predictive markers of lower limb motor recovery after spinal cord injury: a pilot study with an adaptive trial design

Predicting motor recovery in tetraplegia during inpatient rehabilitation by motor unit action potentials and stimulated manual motor testing

STUDY DESIGN

Diagnostic Study.

OBJECTIVES

Early prognosis for recovery in traumatic cervical spinal cord injury resulting in tetraplegia may further guide rehabilitation and surgical interventions. This study assesses the feasibility and potential of using stimulated manual motor testing (SMMT) and needle electromyography (EMG) to predict gains in strength during acute inpatient rehabilitation.

SETTING

Single academic inpatient rehabilitation facility (IRF).

METHODS

Muscles with weak strength (manual motor test (MMT) <3) were assessed for lower motor neuron (LMN) integrity by SMMT using surface electrodes. Muscles without clinical strength (MMT=0) using SMMT and EMG. Correlations and prognostic models assessed the association and prediction of these measures with improvement in MMT values over 4 weeks.

RESULTS

The missing data rate for SMMT and motor unit action potential (MUAP) testing was 9.5% and 24%, respectively. Wilcoxon Rank Sum tests of 4-week MMT changes with MUAP presence (P = 3.89×10-6) and SMMT improvement (P = 0.0156) were statistically significant, but the Spearman Rank Correlation Coefficient of changes in SMMT with MMT changes was not (P = 0.817). The receiver operating characteristic (ROC) Area Under the Curve (AUC) for combined MUAP and SMMT predictors of MMT improvement was 0.732, with an optimal sensitivity of 41.9% (95% CI 25.8% to 58.1%) and specificity of 90.3% (95% CI 84.5% to 96.1%). This model was superior to univariate models.

CONCLUSIONS

With pragmatic compromises in test administration to reduce attrition, measuring the presence of voluntary MUAP and improvement in SMMT during acute rehabilitation retains value in predicting motor improvement in 4 weeks.

Utility of transcranial magnetic stimulation in the assessment of spinal cord injury: Current status and future directions

Comprehensive assessment following traumatic spinal cord injury (SCI) is needed to improve prognostication, advance the understanding of the neurophysiology and better targeting of clinical interventions. The International Standards for Neurological Classification of Spinal Cord Injury is the most common clinical examination recommended for use after a SCI. In addition, there are over 30 clinical assessment tools spanning across different domains of the International Classification of Functioning, Disability, and Health that have been validated and recommended for use in SCI. Most of these tools are subjective in nature, have limited value in predicting neurologic recovery, and do not provide insights into neurophysiological mechanisms. Transcranial magnetic stimulation (TMS) is a non-invasive neurophysiology technique that can supplement the clinical assessment in the domain of body structure and function during acute and chronic stages of SCI. TMS offers a better insight into neurophysiology and help in better detection of residual corticomotor connectivity following SCI compared to clinical assessment alone. TMS-based motor evoked potential and silent period duration allow study of excitatory and inhibitory mechanisms following SCI. Changes in muscle representations in form of displacement of TMS-based motor map center of gravity or changes in the map area can capture neuroplastic changes resulting from SCI or following rehabilitation. Paired-pulse TMS measures help understand the compensatory reorganization of the cortical circuits following SCI. In combination with peripheral stimulation, TMS can be used to study central motor conduction time and modulation of spinal reflexes, which can be used for advanced diagnostic and treatment purposes. To strengthen the utility of TMS in SCI assessment, future studies will need to standardize the assessment protocols, address population-specific concerns, and establish the psychometric properties of TMS-based measurements in the SCI population.