Comparison of Stimulator Triggered Electromyography and SSEP Collision Testing For Assessment of Spinal Cord Stimulator Lateralization Under General Anesthesia Anthony K. Sestokas Division of Intraoperative Neuromonitoring SpecialtyCare Services Group, LLC NANS 2012

Disclosures: None

Co-Authors and Affiliations Vidya M. Bhalodia Anthony K. Sestokas Richard Vogel Joanne Contratti David B. Glassman Connecticut Neuroscience Ashwini Sharan

Spinal Cord Stimulator Placement Under General Anesthesia Advantages Increased Patient Comfort Easier Electrode Placement (decreased pt. movement) Increased Patient Safety Disadvantages No way of verifying extent of paresthesias Radiographic midline may be not be physiologic midline

Neurophysiologic Mapping Techniques for Verifying Stimulator Lateralization Stimulator Triggered Electromyography (StimTrEMG) Activation of spinal cord stimulator (SCS) electrode combinations and recording of indirect (reflexive) motor responses SSEP Collision Testing (SCT) Activation of SCS electrode combinations to “mask” externally generated dorsal column somatosensory evoked potentials

Stimulator Triggered Electromyography (stimTrEMG) Activation of SCS electrode combinations elicits reflexive motor responses from muscles on the left, right or both sides of the body Stimulation Frequency 5 Hz Pulse-width 300 – 500 us Stimulation intensity gradually increased from 0 mA until CMAPs are triggered from one or more myotomes that overlap the dermatomal distribution of pain (or to a maximum of 15 mA) SCS lateralization inferred from pattern and distal extent of myotomal activation on both sides of the body

Stimulator Triggered Electromyography (StimTrEMG) Abdominal Psoas Quadriceps Ant Tib Foot Left Responses Right Responses CMAPs from muscles Stimulation Site Orthodromic Dorsal Column Activation (to thalamus) Antidromic Dorsal Column Activation Synapse with α-motor neuron Spinal Cord

SSEP CollisionTesting (SCT) Activation of SCS electrode combinations blocks somatosensory evoked potentials ascending within the dorsal columns on the left, right or both sides of the spinal cord Stimulation Frequency 60 Hz Pulse-width 300 – 500 us Baseline cortical SSEPs to stimulation of the L/R posterior tibial nerves are recorded before activation of the SCS SSEP testing is then repeated during activation of the SCS SCS lateralization inferred from pattern of SSEP interference on both sides of the spinal cord

SSEP Collision Testing Left PTN SSEP Right PTN SSEP Baselines Collision Orthodromic Dorsal Column Activation (to thalamus) Stimulation Site Antidromic Dorsal Column Activation * Collision Dorsal Column Activation via Peripheral Nerve (to cortex via thalamus) Spinal Cord Posterior Tibial Nerve (PTN) Stimulation

Study Question Does SSEP Collision Testing Provide the Same Information about SCS Lateralization as StimTrEMG?

Methods Retrospective review of dorsal column neurophysiologic mapping data for 40 patients undergoing placement or revision of thoracic spinal cord stimulators Lateralized or midline placement of electrode strip was guided using StimTrEMG mapping technique, stimulating select pairs of electrodes and recording EMG responses from bilateral abdominal, psoas, quadriceps, tibialis anterior, and foot muscles Lateralization vs midline placement of electrode strip was checked using SSEP Collision Testing, stimulating the same pairs of electrodes that were activated for StimTrEMG mapping Results of the 2 techniques were compared across all tested electrode sites

Results StimTrEMG and SSEP Collision Testing was conducted at a total of 96 electrode sites There was no evidence of SSEP collision at 24/96 (25%) electrode sites where StimTrEMG provided evidence of either lateralized or midline placement of the SCS

Results SSEP Collision Test results matched those of StimTrEMG at 50/72 (69%) electrode sites where both techniques provided SCS lateralization information. Discrepancies* occurred at 22/72 (31%) of tested sites * * * *

Summary Collision Testing did not provide information about SCS lateralization at 25% of tested sites When Collision Testing did provide information about SCS laterality, the results were consistent with StimTrEMG results at 69% of tested sites Overall, Collision Testing either failed to provide SCS lateralization information or provided discrepant results (w.r.t. StimTrEMG) at 48% of tested sites

Conclusions SSEP Collision Testing did not provide the same information about SCS lateralization as StimTrEMG at almost half the electrode sites evaluated Differences in the results provided by the two techniques may be due in part to Differential activation of spinal cord pathways by each technique Constraints on the way SSEP Collision Testing was performed in the present study

Further Study Identify factors (electrode type, pt. diagnosis, stimulation parameters) that affect the correlation between StimTrEMG and SSEP Collision Testing results Compare post-operative pain control for SCS placements based on StimTrEMG, SSEP Collision Testing and awake-patient guidance

References Mammis A, Mogilner AY.The use of intraoperative electrophysiology for the placement of spinal cord stimulator paddle leads under general anesthesia. Neurosurgery. 2012 Jun;70(2 Suppl Operative):230-6. Balzer JR, Tomycz ND, Crammond DJ, Habeych M, Thirumala PD, Urgo L, Moossy JJ. Localization of cervical and cervicomedullary stimulation leads for pain treatment using median nerve somatosensory evoked potential collision testing. J Neurosurg. 2011 Jan;114(1):200-5. Epub 2010 May 28. Falowski SM, Celii A, Sestokas AK, Schwartz DM, Matsumoto C, Sharan A. Awake vs. asleep placement of spinal cord stimulators: a cohort analysis of complications associated with placement. Neuromodulation. 2011 Mar-Apr;14(2):130-4 Shils JL, Arle JE. Intraoperative Neurophysiologic Methods for Spinal Cord Stimulator Placement Under General Anesthesia. Neuromodulation. 2012 Jun 1

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