Cortical motor reorganization after paraplegia

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Abstract
Objective: To determine whether a previously identified posterior reorganization of the cortical motor network after spinal cord injury (SCI) is correlated with prognosis and outcome. Methods: We applied the techniques of high-resolution EEG and dipole source analysis to record and map the motor potentials (MPs) of the movement-related cortical potentials in 44 patients after SCI. Twenty normal controls were also tested. Results were analyzed using a distance metric to compare MP locations. EEG was coregistered with individual specific MR images and a boundary element model created for dipole source analysis. Results: MPs with finger movements were mapped to a posterior location in 20 of 24 tetraplegics compared with normal controls. Two patients, one studied 4 and one 6 weeks after injury, initially had posterior MPs that, on serial testing, moved to an anterior position with recovery. Dipole source localization of the MP generators confirmed these results. Nine of 20 paraplegics had a posterior MP location with actual or attempted toe movements. All 5 patients who could move their toes had posterior MPs. The MP was posterior in 4 of the 15 paralyzed patients. This is a significant difference in proportions. The only patient with paraparesis whose testing was repeated had an MP that moved to an anterior position with recovery. Conclusions: Posterior reorganization has a significant relationship to prognosis in paraplegia and is reversed in some SCI patients who recover function. Posterior reorganization may result from a preferential survival of axons that originate in somatosensory cortex and contribute to the corticospinal tract. These preliminary results should be verified by a larger prospective study.