Does Post-Tetanic Transcranial Stimulation Augment the Wave Amplitudes of Spinal Cord Evoked Potential (Tc-SCEP)?

Study design: Prospective within-subjects study.

Objectives: Although motor-evoked potential (MEP) amplitude can reportedly be increased by tetanic stimulation of the peripheral nerves before transcranial electrical stimulation (TES), no reports have described on whether tetanic transcranial stimulation augments the wave amplitudes of spinal cord-evoked potentials (Tc-SCEP). The primary purpose of this study was to investigate whether tetanic stimulation induces waveform amplification of Tc-SCEP. The secondary purpose was to elucidate the mechanism of the amplification effect of tetanic stimulation.

Methods: We recruited 20 patients who underwent cervical or thoracic spine surgeries. We compared the compound muscle active potentials (CMAPs) of Tc-MEP and Tc-SCEP before and after tetanic stimulation of the median or tibial nerve.

Results: Although the CMAP wave amplitudes of the abductor pollicis brevis (APB) and abductor hallucis (AH) showed significant enlargement on Tc-MEP following tetanic stimulation of the median and tibial nerves, an augmentation effect regarding Tc-SCEP (203 μV [without tetanic stimulation], 212 μV [tetanic stimulation of the median nerve], and 208 μV [tetanic stimulation of tibial nerve]) could not be demonstrated.

Conclusion: Although MEP amplitudes can be enlarged by tetanic stimulation of the peripheral nerves, the amplification mechanism may not involve the lateral corticospinal tract from the brain stem to the anterior horn.