Intraoperative spinal cord monitoring using low intensity transcranial stimulation to remove post-activation depression of the H-reflex

Publication date: October 2016
Source:Clinical Neurophysiology, Volume 127, Issue 10
Author(s): Jennifer C. Andrews, Richard B. Stein, Kelvin E. Jones, Douglas M. Hedden, James K. Mahood, Marc J. Moreau, Eric M. Huang, François D. Roy
ObjectiveTo investigate whether low intensity transcranial electrical stimulation (TES) can be used to condition post-activation depression of the H-reflex and simultaneously monitor the integrity of spinal motor pathways during spinal deformity correction surgery.MethodsIn 20 pediatric patients undergoing corrective surgery for spinal deformity, post-activation depression of the medial gastrocnemius H-reflex was initiated by delivering two pulses 50–125ms apart, and the second H-reflex was conditioned by TES.ResultsLow intensity TES caused no visible shoulder or trunk movements during 19/20 procedures and the stimulation reduced post-activation depression of the H-reflex. The interaction was present in 20/20 patients and did not diminish throughout the surgical period. In one case, the conditioning effect was lost within minutes of the disappearance of the lower extremity motor evoked potentials.ConclusionPost-activation depression was used to detect the arrival of a subthreshold motor evoked potential at the lower motor neuron. The interaction produced minimal movement within the surgical field and remained stable throughout the surgical period.SignificanceThis is the first use of post-activation depression during intraoperative neurophysiological monitoring to directly assess the integrity of descending spinal motor pathways.



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