Differences in Cortical Gray Matter Atrophy of Paraplegia and Tetraplegia after Complete Spinal Cord Injury.

Anatomical studies of SCI using Magnetic Resonance Imaging (MRI) report diverging observations, from 'no changes' to 'tissue atrophy in motor and non-motor regions.' These discrepancies among studies can be attributed to heterogeneity in extent, level and post-injury duration observed within the SCI population. But, no studies have investigated structural changes associated with different levels of injury (paraplegia vs. tetraplegia). High-resolution MRI images were processed using Voxel-Based Morphometry technique to compare regional GM volume (GMV) between 16 complete paraplegia and 7 complete tetraplegia SCI subjects scanned within two years of injury when compared to 22 age-matched healthy controls using one-way Analysis of Covariance (ANCOVA). A post-hoc analysis using region of interest based approach was employed to quantify GMV differences between healthy controls and subgroups of SCI. A voxel-wise one sample t-test was also performed to evaluate the mean effect of post-injury duration on GMV of SCI group. ANCOVA resulted in altered GMV in inferior frontal gyrus, bilateral mid orbital gyrus extending to rectal gyrus and anterior cingulate cortex. Post-hoc analysis, in general, indicated GM atrophy after SCI but tetraplegia showed a greater decrease in GMV when compared to paraplegia and healthy controls. Further, the GMV of the middle frontal gyrus, superior frontal gyrus, inferior frontal gyrus, insula, mid-orbital gyrus and middle temporal gyrus was positively correlated with post-injury duration in both paraplegia and tetraplegia groups. GM atrophy after SCI is affected by the level of cord injury, with higher levels of injury resulting in greater loss of GMV. The magnitude of GMV loss in the frontal cortex after SCI also appears to be dynamic within the first two years of injury. Understanding the effect of injury level and injury duration on structural changes following SCI can help better understand the mechanisms leading to positive and negative clinical outcome in SCI patients.