Classifying and predicting endurance outcomes of α2-adrenergic agonist intervention in spinal cord injury

Spinal cord injury (SCI) is a traumatic condition that can lead to both functional and neuromuscular impairments. Spasticity in the muscles surrounding the ankle joint caused by hypertonia is often reported as a complication. We investigated whether a pharmacological intervention using Tizanidine, an anti-spastic medication acting as an α₂-adrenergic agonist, could lead to improvements in walking endurance. We placed subjects on a 4-week program and measured the change in clinical measures of walking speed, endurance, and mobility. We used growth mixture modeling (GMM) to class subjects into groups based on recovery patterns. Two classes of recovery were found by GMM: high and low functioning. Radom coefficient regression (RCR) was then used to identify significant changes over time. Statistically significant improvements in walking endurance were shown for the high functioning group. However, a small number of subjects in the high functioning group showed improvement greater than the smallest real difference (SRD), which indicates a clinical significance as well. We also investigated the extent to which these recovery patterns can be predicted using baseline measures. Baseline walking endurance was found to be a robust predictor of recovery in walking endurance. Subjects that began the intervention with already higher endurance showed a greater chance of improvement in endurance over time. This information could potentially be used as a fast and reliable assessment tool for clinicians to predict which patient can benefit the most from this intervention prior to prescribing the medication, and thus optimizing cost and resources. Our findings demonstrate that these techniques can be used to characterize and predict the progress of changes to functional impairments due to various types of intervention.