Transcript Spinal Cord Stimulation Mechanisms and Indications

Douglas Dobecki, M.D.
San Diego Pain Institute
Gate Control Theory of SCS
•Originally derived from gate
control theory by Melzack and
Wall
•Peripheral stimulation of Aβ
fibers leads to activation of
inhibitory interneurons and
subsequent inhibition of
second order nociceptive
neurons in the dorsal horn
•Expanded to electrical
stimulation of the dorsal
column with production of
paresthesia
Melzack et al, Science, 1965, Vol 150
Shealy, et al, Anesthesia and Analgesia, 1967, Vol 46
Neurophysiologic Mechanisms of
SCS
•SCS increases dorsal horn
inhibitory neurotransmitter
GABAB, while decreasing
excitatory amino acids Glutamate
and Aspartate
•Activation of descending
somatosensory control pathways
through release of Serotonin,
Norepinephrine, Adenosine
•Suppression of sympathetic
activation by modulation of αadrenoreceptors and antidromic
release of calcitonin gene-related
peptide (CGRP) and Substance P
•Modulation of WDR neurons
Meyerson et al, Journal of Pain and Symptom Management, April 2006, Vol 31, No 4S
Electrophysiologic Mechanisms of SCS
•Current flows from Cathode (-
) to Anode (+) resulting in
neuronal depolarization at
Cathode (-) and
hyperpolarization at Anode (+)
•Electrical parameters are
adjusted during programming
including electrode polarity,
Frequency (Hz), Amplitude (V
or ma), and Pulse Width (μs)
•Potential segmental
conductance blockade of
spinothalamic tracts
•Many theories on the mechanisms of action of spinal cord
stimulation have been suggested, including gate inhibition,
activation or release of purported neuromodulators, conductance
blockade of spinothalamic tracts, blockade of sympathetic
mechanisms, and activation of supraspinal mechanisms
•The mechanism of spinal cord stimulation cannot completely
explained by one model
•It is likely that multiple mechanisms and neurophysiologic
pathways operate sequentially or simultaneously
•Indicated for the management of chronic and intractable pain of
the trunk or extremities
•Patients have failed adequate trial of conservative and
conventional therapies
•Patients have passed psychological screening
•Common conditions include
• Failed Back Surgery Syndrome/Post-Laminectomy Syndrome
• Complex Regional Pain Syndrome (CRPS)
• Arachnoiditis
• Chronic Radiculopathy
• Epidural Scarring or Fibrosis
• Chronic Neuropathy or Neuralgia
• Post-Thoracotomy Pain
Failed Back Surgery Syndrome
 Defined as persistent or recurrent complaints of low back and/or leg
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pain in patients who have undergone operative procedures intended to
relieve those complaints
Can occur in up to 10-40% of spine surgeries
$20B annually in direct health care costs
5th most common reason for MD visit
Important to identify and treat other etiologies of FBSS that are not
neuropathic and not candidates for SCS
 Foraminal stenonsis, discogenic pain, recurrent disc herniation,
pseudoarthrosis, facetogenic pain, sacroiliac syndrome
Common psychological disorders in FBSS
 Depression, anxiety, personality disorders, and secondary gain
issues
North et al, Neurosurgery, 2005, Vol 56, No 1
Follet et al, Neurosurgery Quarterly, March 1993, Vol 3, Issue 1
Failed Back Surgery Syndrome Etiology
Genesis is multifactorial
 Improper patient selection
 Inadequate operations
 Operative complications
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Epidural scarring, fibrosis,
arachnoiditis,
Pseudoarthrosis
Hardware malposition or failure
 Progression of degenerative
processes
 Onset of new pathology
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Altered joint mobility
Spondylolisthesis
Adjacent segment disease
Follet et al, Neurosurgery Quarterly, March 1993, Vol 3, Issue 1
Park et al, Spine, September 2004, Vol 29, Issue 17
Clinical Effectiveness of SCS in FBSS
•SCS was more successful than re-operation in giving selected FBSS patients
at least 50% pain relief
•Minimally invasive therapeutic trial is an important advantage versus
reoperation
•In most cases, SCS eliminated the need for further spine surgery in patients
identified as reoperation candidates by standard criteria
•Battery life is a major SCS cost driver. Lifetime savings of rechargeable SCS
systems can exceed $300,000 for average patient.
•24 month outcomes demonstrate significant improvements of SCS patients
compared to conventional medical management (CMM) group. Significantly
more SCS (47%) patients versus CMM (7%) achieved the primary outcome of
greater than 50% pain relief (P=0.02).
North et al, Neurosurgery, January 2005, Vol 56, No 1
North et al, Neuromodulation, 2004, Vol 7
North et al, Neurosurgery, August 2007, Vol 61, Issue 2
Kumar et al, Neurosurgery, October 2008, Vol 63, No 4
Complex Regional Pain Syndrome
 Describes a myriad of pain symptoms which
bridge neuropathic and vasculopathic pain
conditions
 Symptoms are typically regional and out of
proportion to the clinical course of the inciting
event
 CRPS Type 1- pain symptom development
without evidence of nerve injury
 CRPS Type 2- pain symptom development in
setting of obvious nerve injury
 Sympathetically Maintained Pain (SMP)
 Sympathetically Independent Pain (SIP)
Bennett et al, Neuromodulation, July 1999, Vol 2, Issue 3
Complex Regional Pain Syndrome
Diagnosis based on history and physical exam
Report 1 symptom in 3 of 4 categories:
* Sensory- hyperesthesia and/or allodynia
* Vasomotor- temperature asymmetry and/or skin color changes
* Sudomotor /Edema- edema and/or sweating changes
* Motor/Trophic- decrease ROM and/or motor dysfunction and/or trophic
changes
Must display at least 1 sign in 2 or more categories:
* Sensory- hyperesthesia (pin prick) and/or allodynia (mechanical,
Temperature) and/or deep somatic pressure/joint movement
* Vasomotor- temperature asymmetry (>1 C) and/or skin color changes
* Sudomotor /Edema- edema and/or sweating changes
* Motor/Trophic - decrease ROM and/or motor dysfunction
(weakness, tremor, dystonia, and/or trophic changes)
Hayek et al, The Physician and Sports Medicine, May 2004, Vol 32, No. 5
Evidence Supporting SCS for CRPS
Reference
Type of Study
(Level of Evidence)
N
Outcome
Kemler et al. 2000
RCT (level 2)
36 pts.
Improved pain and quality of
life Successful in 56% of
patients at 6 months
Kemler et al. 1999
Retrospective (level 3)
23 pts.
Successful in 57% of patients
Kemler et al. 2004
RCT (level 2)
36 pts.
Successful in 63% of pts; 2 yr
follow-up of Kemler et al.
2000
Bennett et al. 1999
Retrospective (level 3)
101 pts.
70% pt satisfaction for 1 lead
91% pt satisfaction for 2 leads
Kumar et al. 1997
Nonrandomized (level 3)
12 pts.
Good relief in 4 pts.
Excellent relief in 8 pts.
*RCT = randomized controlled trial
• An understanding of the mechanisms of spinal cord
stimulation continues to evolve
• SCS has been proven to be sustainably effective in the
treatment of chronic neuropathic pain in several modern
randomized clinical trials versus conventional therapies or
reoperation
• Routine trial stimulation and an improved understanding of
appropriate indications are associated with increased
patient satisfaction, functional capacity and quality of life
• Rational use of SCS will continue to expand and continuing
technological advancements will continue shape treatment
algorithms