Evident transsynaptic degeneration of motor neurons after spinal cord injury: a study of neuromuscular jitter by axonal microstimulation.

Neuronal degradation accompanied with axonal degeneration has been known to occur in spinal motor neurons after an upper level of spinal cord lesion. In the present study, the functional integrity of neuromuscular transmission was assessed by utilizing a sensitive electrodiagnostic method comprising of stimulated single-fiber electromyography (SFEMG), along with axonal microstimulation, in paralytic muscles of patients with spinal cord injury (SCI). Neuromuscular jitter was measured in anterior tibial muscles for 30 patients with SCI and also for 12 normal controls. Mean jitter of 37.4 +/- 14.7 (mean +/- SD) micros, as obtained in SCI patients, was found to be significantly greater than the results of 20.1 +/- 8.4 micros in normal controls (P < 0.01). Jitter measurement was not significantly different in varied functional scales of SCI. A positive correlation was noted between the increased jitter and the disease duration from the onset of cord lesion till the time of stimulated SFEMG test (r = 0.68; P < 0.01). The present abnormal finding of neuromuscular jitter provides an electrophysiologic evidence for axonal degeneration and suggests that transsynaptic degeneration of motor neuron may occur below the level of cord lesion in SCI patients. Furthermore, the neuronal degradation in SCI was positively correlated with the course duration of the disease.