Effect of corticospinal and reticulospinal tract damage on spastic muscle tone and mobility: a retrospective observational MRI study.

Abstract

Spastic muscle tone, often observed after spinal cord injury (SCI), is thought to contribute to body support during walking at a lower level of neural organisation. Understanding the link between damage to specific spinal tracts and the development of spastic muscle tone and mobility could enhance our knowledge of the neural structures crucial for recovery of function after SCI. In this retrospective observational study, MRI-based assessments of descending spinal tract damage were related to the development of spastic muscle tone and mobility. Focal damage to the corticospinal (CST) and reticulospinal tracts (RST) was assessed on transversal T₂-weighted scans of 49 patients with SCI one month post-injury. The extent of tract damage was then associated with the degree of spastic muscle tone measured by the Modified Ashworth Scale (MAS), and changes in mobility subscore of the Spinal Cord Independence Measure (SCIM). The extent of CST damage was predictive for the level of MAS score with a positive relationship (β = 0.043, SE = 0.016, OR: 1.044, 95% CI: 1.014-1.080, P = 0.006). This association was negatively modulated by the interaction between CST and RST damage (β = -0.002, SE = 0.001, OR: 0.998, 95% CI: 0.997-0.999, P = 0.004)-i.e. extensive RST damage weakened the relationship between CST damage and MAS score. The extent of RST damage was related to the change in SCIM mobility subscore, independent of MAS score (β: -0.683, SE = 0.231, 95% CI: -1.135 to -0.230, P = 0.007). The extent of CST damage, along with the preservation of the RST, reliably predicts spastic muscle tone, while preserved RST structure alone serves as an independent predictor of mobility outcomes. These observations highlight the role of the reticulospinal system in the functional recovery of mobility and may have broader relevance for other neurological conditions with spinal cord involvement. Swiss National Science Foundation.