Clinical syndromes associated with disproportionate weakness of the upper versus the lower extremities after cervical spinal cord injury.

Patients with cervical spinal cord injuries who present with weakness or paralysis of the hands and arms with relative preservation of lower extremity strengths are often categorized as having two clinical syndromes, cruciate paralysis and acute central cervical spinal cord injury. The explanation for the pathophysiological findings of the dissociated strength in the upper versus the lower extremities has relied on the assumption that there is a localized injury within a somatotopically organized corticospinal tract. This article summarizes the evidence that there is no somatotopic organization within the corticospinal tract in the medulla or cervical spinal cord in primates. An alternative hypothesis for these two syndromes is presented and is based on evidence that has demonstrated that the corticospinal tract in primates is critical for hand function but not for locomotion. Other prevailing theories are reviewed. Thus, we propose that a syndrome consisting of relatively greater hand and arm weakness compared with leg weakness can occur after an injury to the corticospinal tracts in the medulla or the cervical cord. The proposed mechanism, based on the function of the corticospinal tract, unifies a spectrum of injuries of the lower medulla and cervical spinal cord, which produce similar clinical syndromes (cruciate paralysis and acute central cervical spinal cord injury).