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

. 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.