1. 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

2. Disclosures:
None

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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 * * * *

14. 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

15. 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

16. 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

17. References
Mammis A, Mogilner AY.The use of intraoperative electrophysiology for the placement of spinal cord stimulator paddle leads under general anesthesia. Neurosurgery 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 Jan;114(1): Epub 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 Mar-Apr;14(2):130-4
Shils JL, Arle JE. Intraoperative Neurophysiologic Methods for Spinal Cord Stimulator Placement Under General Anesthesia. Neuromodulation Jun 1

18. Thank You