Long-Latency Motor Evoked Potentials in Spinal Cord Injury

Long-Latency Motor Evoked Potentials
in Spinal Cord Injury
David S. Barnkow, Au.D., D.ABNM, CNIM, CCC-A
Directory of Quality Assurance
Medsurant, LLC
Denver, Colorado, USA
Peter A. Raudzens, M.D., F.R.C.P, (C)
Chief Medical Officer, Medsurant Holdings, LLC
Chairman, Sensory Testing Systems
Phoenix, Arizona, USA
Intraoperative Neurophysiology in Neurosurgery – Part III
Spine and Spinal Cord Surgery
Lazise, Italy October 19, 2012

Long-Latency Motor Evoked Potentials in Spinal Cord Injury
D. Barnkow & P. Raudzens, October 19, 2012
Case 1, The Beginning:
• Patient: 56 year old male, 13 year post-injury
• Dx: cervicothoracic syrinx, post-operative ataxia, myelopathy,
post-traumatic tethered spinal cord
• Chief Complaint: progressive lower extremity dysfunction,
sensory/motor loss and bladder dysfunction
• Previous Surgeries:
• ACDF C5-7, 1995
• PSF C3-7 1995
• syringosubarachnoid shunt T1-2, 3/2000
• shunt revision, 9/2000
• revision syringosubarachnoid shunt T1-3, 2004
• spinal cord untethering, 2005
• thoracic shunt removal and lumbar drain placement, 12/2005
• CSF leak repair, 1/2006
• wound debridement and mesh removal, 7/2006
• shunt revision, 7/2006
• ventriculopleural shunt, 8/2006
• new syringosubarachnoid shunt, 2/2007
• Procedure: cervical laminectomy, spinal cord untethering,
expansion duraplasty

Case 1, The Beginning:
• Primary AbH response 50.29 ms, LLMEP approx. 90 ms
• C4’ anodal transcranial electrical mMEPs
• Intensity: 160-220V, Train: 6, ISI: 2, Pulse Width 200 usec

• Literature search for Long-Latency MEPs revealed a
paucity of publication related to spinal cord injury.
• References
• Dimitrijević et al. Early and late lower limb motor evoked potentials elicited by
transcranial magnetic motor cortex stimulation. 1995
• Vandermeeren et al. Long-latency motor evoked potentials in congenital
hemiplegia. 2003
• Bastings et al. Mechanisms of hand motor recovery after a stroke: an
electrophysiological study of central motor pathways. 1997
• Calancie et al. Motor-unit responses in human wrist flexor and extensor
muscles to transcranial cortical stimuli. 1987
• Heald et al. Longitudinal study of central motor conduction time following
stroke. 1. Natural history of central motor conduction. 1993
• Rapisarda et al. Can motor recovery in stroke patients be predicted by early
transcranial magnetic stimulation? 1996
• Turton et al. Contralateral and ipsilateral EMG responses to transcranial
magnetic stimulation during recovery of arm and hand function after stroke.
1996

Introduction:
• Previous studies in children with congenital
hemiplegia and adults with stroke of have
demonstrated muscle motor evoked potentials
(mMEPs) to transcranial magnetic stimulation with
repeatable response latencies significantly longer
than anticipated for typical corticospinal tract
mediated mMEPs.
• Intraoperative assessment of individuals with pre-
existing spinal cord injury (SCI) using transcranial
electric mMEPs recorded with epochs greater than
100 milliseconds has also revealed a frequent, but
not universal, appearance of long-latency motor
evoked potentials (LLMEPs).
• Research Question: “Are LLMEPs clinically
significant to spinal cord injury?”

Material and Methods:
• A retrospective review of intraoperative mMEP data
obtained over a five year period from individuals with pre-
existing SCI undergoing spine surgery identified LLMEPs
in 150 of 356 cases (42%).
• Stimulus and recording parameters followed established
clinical techniques. Recording epochs ranged from 100
ms to 300 ms.
• These six case studies were chosen to illustrate the
LLMEPs observed in individuals with SCI over a broad
range of etiologies, spinal levels, injury severity, and
post-injury duration, as well as the variety of LLMEP
characteristics.

• Case 2, 44 y/o female,
C12DB-067
• Hx: C6 Incomplete
quadriplegia, ASIA D,
Brown-Sequard Type
cord injury due to Motor
Vehicle Accident.
• CC: Loss of function in
arms and legs requiring
a cane to ambulate.
• Dx: Post-traumatic
tethered spinal cord with
myelocystocele.
• Procedure: Spinal cord
untethering and
subarachnoid peritoneal
shunt.

• Case 2, 12DB-067, C6, ASIA D, Dx: Brown-Sequard.
• Note: Contralateral LLMEP threshold below ipsilateral mMEP.

• Case 3, 50 y/o male C12DB-067
• Hx: Thoracic spinal cord
cavernous hemangioma
with bleeding and right
cerebellar cavernous
hemangioma with bleeding
16 years previously.
Required a cane to
ambulate.
• CC: Increasing weakness in
both legs, right worse than
left. Decreased sensation
left worse than right.
• Dx: T8 post-traumatic
tethered cord, ASIA D, L2-4
spinal stenosis, acquired
scoliosis.
decompression and PSF w/
instrumentation T10-L5.

• Case 3, 50 y/o male C12DB-067
• Hx: Thoracic spinal cord
with bleed, right cerebellar
with bleed 16 years
previously. Required a cane
to ambulate.
• CC: Increasing weakness in
both legs, right worse than
left. Decreased sensation
left worse than right.
• Dx: Post-traumatic tethered
spinal cord, ASIA D, L2-4
spinal stenosis, acquired
scoliosis.
decompression and PSF w/
instrumentation T10-L5.

• Case 3, C12DB-067, 50 y/o male Hx: Thoracic spinal cord and right cerebellar cavernous
hemangioma with bleed,
• Note: Robust LLMEP in left Gracilis/VL and contralateral abductor hallucis.

• Case 4: 44 y/o male C011DSB-077
• Hx: C4 incomplete quadriplegia due to diving
injury 20 years previously. ACDF C2-5 at time
of injury. Subsequent ACDF C6-7.
• CC: increasing spasticity, neck pain upon
flexion and neuropathic pain.
• Dx: C5-6 3mm retrolisthesis, post-traumatic
tethered cord, C4 ASIA C
• Procedure: Anterior discectomy and spine
fusion C5-6

• Case 4: 44 y/o male C011DSB-077, C4 incomplete quadriplegia
• Note: LLMEPs in bilateral brachioradialis and contralateral pronator teres and
APB

• Case 5, 16 y/o female, NB-081216
• CC: 2 day history of low back pain upon flexion
following a fall from a handstand. No sensory,
motor or bowel/bladder complaints.
• Dx: L1 burst fracture.
• Procedure: T12-L2 posterior spine fusion with
bone morphogenic protein for fusion.

• Case 5, 16 y/o
female, L1 burst
fracture, NB-081216
• 14:48: pre-positioning
• 14:54: post-positioning
• 15:11: incision
• 15:28: exposure
complete
• 15:31: L1
decompression and
reduction
• 15:51: decompression
complete, begin
pedicle screws
• 16:31: placing rods

• Case 6: 62 y/o male, CO11DSB-123, 30 years post-injury, C6
tetraplegia due to wrestling accident, ASIA
Impairment Scale A
• CC: Recent onset neuropathic pain, decreased
sensation, increased spasm
• Dx: C5-C6 intramedullary cyst with cystic changes
ascending to C1-2.
• Procedure: cervical laminectomy, spinal cord
untethering, expansion duraplasty, subarachnoid-
peritoneal shunt placement.

• Case 6: 62 y/o male, CO11DSB-123, C6 tetraplegia.
• Note: Contralateral threshold 80V below target muscle

Results:
• LLMEPs were observed alone and in the presence
of typical mMEPs.
• LLMEPs were observed in the target muscles
alone, in the non-target muscles alone or
simultaneously in bilateral muscle pairs.
• LLMEPs were observed in muscles innervated
from above, at, and below the level of SCI.
• LLMEPs demonstrated wide variations in
morphology, latency, amplitude, and stimulation
threshold relative to typical mMEPs.

• Y. Vandermeeren et al. (2003)
• “Long-latency MEPs have been
described in normal subjects, and
anecdotally reported in CH patients,
but their origin is still controversial
and their prognostic value has never
been explicitly investigated.”
• The same statement appears true for
LLMEPs in Spinal Cord Injury in
2012.

Conclusions:
• LLMEPs can be easily collected with simple
recording epoch (time sweep) adjustment.
• LLMEPs present a variable constellation of
characteristics over the broad continuum of SCIs.
• Additional data and meta-analysis are needed to
determine if LLMEPs are an important prognostic
indicator of spinal cord status.
• A theoretical model for the generation of LLMEPs in
SCI is needed.

• References
• Dimitrijević MR, Koflera M, McKay WB, Sherwood AM, Van der Lindenb C, Lissensc MA. Early and late
lower limb motor evoked potentials elicited by transcranial magnetic motor cortex stimulation.
Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section. 85, 6, (1992), 365–373
• Vandermeeren Y, Bastings E, Fadiga L, Olivier E. Long-latency motor evoked potentials in congenital
hemiplegia. Clin Neurophys. 114, (2003) 1808-1818
• Bastings E, Rapisarda G, Pennisi A, Maertens de Noordhout A, Delwaide PJ. Mechanisms of hand motor
recovery after a stroke: an electrophysiological study of central motor pathways. J Neurol Rehab 1997;
11:97–108
• Calancie B, Nordin M, Wallin U, Hagbarth KE. Motor-unit responses in human wrist flexor and extensor
muscles to transcranial cortical stimuli. J Neurophysiol 1987;58:1168–85
• Heald A, Bates D, Cartlidge NEF, French JM, Miller S. Longitudinal study of central motor conduction time
following stroke. 1. Natural history of central motor conduction. Brain 1993a;116:1355–70
• Heald A, Bates D, Cartlidge NEF, French JM, Miller S. Longitudinal study of central motor conduction time
following stroke. 2. Central motor conduction measured within 72 h after stroke as a predictor of functional
outcome at 12 months. Brain 1993b;116:1371–85
• Rapisarda G, Bastings E, Maertens de Noordhout A, Pennisi G, Delwaide PJ. Can motor recovery in
stroke patients be predicted by early transcranial magnetic stimulation? Stroke 1996;27:2191–6
• Turton A, Wroe S, Trepte N, Fraser C, Lemon RN. Contralateral and ipsilateral EMG responses to
transcranial magnetic stimulation during recovery of arm and hand function after stroke. Electroenceph clin
Neurophysiol 1996;101:316–28.

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