The variability of representation and latency of the F-wave in patients at different periods of spinal cord injury

Introduction. Neurophysiological examination in patients with spinal cord injury is advisable to determine the end of the period of spinal shock. F-wave is a late electromyographic phenomenon realized by activating a pool of motor neurons of the anterior horns of the spinal cord. In the state of spinal shock, the duration of which is variable, F-waves are not recorded. The presence of F-waves from the tibial nerves indicates the completion of spinal shock and restoration of electrical excitability of motor neurons of the anterior horn of the spinal cord. The appearance of F-waves is a marker for diagnostic transcranial magnetic stimulation to assess the viability of the cortical-spinal tract in the early stages of spinal shock.

Study aim. To analyze the representation of F-waves in patients in different periods of spinal shock, depending on the level, volume and duration of the lesion.

Materials and methods. There were a total of 15 patients with spinal trauma in age from 19 to 29 years enrolled. All patients affected were localized in segments C4–C7. The examination included stimulation electroneuromyography: registration of motor responses, sensory responses and F-waves from the median, ulnar, fibular and tibial nerves on both sides.

Results. In 5 patients: 3 in acute, 1 in early and 1 in late periods of spinal cord injury, spinal shock was clinically diagnosed: electromyographic revealed the absence of F-waves for all tested nerves. In 4 patients in the early period of spinal cord injury F-waves were registered only with n. tibialis, the first spontaneous movements in the limbs were clinically observed; in 6 patients in the intermediate and late periods of spinal cord injury f-waves were recorded from all the nerves under study with constant latency. The end of spinal shock was clinically verified, with the presence of a minimum volume of movements and restoration of sensitivity in individual segments.

Conclusion. Registration of F-wave should be a mandatory component of stimulation electromyographic in the verification of spinal shock, the duration of which is not correlated with the periods of spinal cord injury. The presence of f-waves is a diagnostic marker for transcranial magnetic stimulation to assess the viability of the cortical-spinal tract.

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