[MEPs by transcranical magnetic stimulation in experimental acute spinal cord injury]

The efficacy of motor evoked potentials (MEPs) induced by magnetic brain stimulation was investigated experimentally for assessing acute spinal cord injury. Twenty-five rabbits were employed for the acute spinal cord injury model. Following laminectomy under intravenous and intraperitoneal anesthesia, the spinal cord at the level of the fifth lumbar vertebra wsa injured by Allen's weight drop method. MEPs from the tibialis anterior muscle (M-MEP) were recorded using bipolar electrodes: prior to the injury; immediately after the injury; at 30 min, 1 hour, 3 hours, and at 5 hours after the injury. MEPs from the spinal cord (S-MEP) were recorded proximal to and distal from the injury site using epidural tube electrodes. Subjects were divided into two groups; complete and incomplete paralysis, according to the degree of motor dysfunction at 1 week after the injury. All the 13 subjects with incomplete paralysis had shown immediately after the trauma a prolongation in the M-MEP latency, with a polyphasic wave form seen in 5 of them. In 3 cases, the amplitude of the M-MEPs was decreased without any change in wave form. In others, there was some variation in the change of wave form, but there was no relationship found between the change of wave form and the degree of motor dysfunction in this group. Histopathologically, infiltration of the inflammatory cells and diffuse hemorrhaging were seen in the gray matter of the injured spinal cord in the incomplete paralysis group. In 7 of the 10 cases with complete paralysis, the M-MEP disappeared within 3 hours. Histopathologically, large areas of the nerve cells disappeared from the gray matter in this group. The S-MEP disappeared immediately after trauma in the group with complete paralysis as well as in those with incomplete paralysis. This study indicated that MEPs taken immediately after a trauma may predict the severity of a spinal cord injury and were useful for evaluating the prognosis of motor function during the acute phase of a spinal cord injury.