Transcript Neuropathic Pain

Spinal Cord Stimulation for Pain
Alon Y. Mogilner, MD, PhD
Associate Professor of Neurosurgery
Director, Center for Neuromodulation
NYU Langone Medical Center
Disclosures
• Medtronic neurological:
– Consultant, fellowship/grant support
• St. Jude Medical:
– Grant support, consultant
• Boston Scientific
– Grant Support
Pain: Anatomy and Physiology
• Nociceptive pain:
– Pain arising from a result of tissue damage and concomitant activation
of nociceptors (sensory receptors) in the peripheral nervous system
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Trauma
Inflammation
Visceral distention
Neoplastic infiltration
– Described as “sharp, aching, throbbing”
• Neuropathic pain:
– Pain arising from a lesion or dysfunction in the peripheral or central
nervous system
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Radiculopathy
Postherpetic neuralgia
Peripheral neuropathy
Central (post-stroke) pain
– Described as “burning, electrical, tingling, shooting”
Neuromodulation
• Generally used for neuropathic pain
– Dysesthesias- Unfamiliar, unpleasant sensations
often burning or electrical
– Paresthesias- paroxysmal, shooting, stabbing
– Allodynia- mild stimuli are perceived as painful
Neuropathic Pain
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Sustaining Mechanisms
– Primary afferent or CNS
nociceptive hyperactivity
– loss of central inhibitory
mechanisms
– increased sympathetic efferents
Gate theory of pain
• Introduced by Melzack and Wall
• Stimulation of large myelinated Aß fibers
results in paresthesias that block the activity
of small A∂ (thinly myelinated), and C (nonmyelinated) fibers.
History of spinal cord stimulation
• Spinal cord stimulation (SCS) was first used in the late 1960s
and 1970s.
• The first fully implantable system was available in the early
80s.
• It is most commonly used in the US for the treatment of
Complex regional pain syndrome (CRPS) or Failed Back surgery
syndrome (FBSS), but is more often used in Europe for
treatment of peripheral vascular disease and non-operative
angina.
How does it work?
• SCS is thought to
activate paininhibiting neuronal
circuits within the
dorsal horn and
inducing
paresthesias.
Modified Gate Control
Effects on neurotransmitters
SP content in human CSF also appears to increase as a result of therapeutic SCS
GABA and glycine increase in DH of rats with SCS;
GABA-B antagonists counteract the effects of SCS.
Supraspinal effects
• The activation of supraspinal circuits is also
evident from a growing number of studies
– microdialysis studies on transmitter release in the
PAG of the rat
– positron emission tomography in angina patients
submitted to SCS
– changes in c-fos and stress proteins in the rat with
experimental SCS
Other forms of stimulation
• All thought to involve gate theory
• Local effects based on area being stimulated.
• With upstream or downstream effects, based
on location.
• Neuromodulatory device usually placed
proximally to region suspected to be
aberrantly firing.
SCS: General Overview
• Indications:
– Neuropathic pain syndromes
• Failed Back Surgery Syndrome (FBSS)
– Most common indication in US for SCS
– Aka Post laminectomy syndrome
– Persistent pain in the back and legs despite spinal surgery
• Complex Regional Pain Syndrome (CRPS, RSD)
• Neuropathies of varying etiologies
– Diabetes, Vascular disease, HIV, idiopathic, neoplastic
• Ischemic disease
– More commonly used in Europe
» Angina
» PVD
SCS: Patient Selection
• Most common clinical indications:
– Post laminectomy syndrome, aka “failed back
surgery syndrome” (FBSS)
• Persistent pain in the back and legs despite spinal
surgery
– Complex regional pain syndrome (CRPS), aka RSD
(Reflex sympathetic dystrophy) of the limbs
– Angina Pectoris
– Ischemic pain of the limbs
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So which patients may benefit from
neuromodulation?
(Based on SCS data)
1) pain not associated with malignancy;
2) poor response to conservative treatment for at least 6
months
3) remedial surgery inadvisable
4) no major psychiatric disorder, including somatization
complaints
• 5) willingness to stop inappropriate drug use before
implantation
• 6) no secondary gain or litigation involved
• 7) ability to give informed consent for the procedure.
The supporting literature for patient
selection for spinal cord stimulation
• The clinical factors that were found to be
reliable indicators for a good response to SCS
in FBSS at 10 year follow up were:
– 1) early treatment (0–3 years) after first failed
back surgery;
– 2) predominance of neuropathic leg pain;
– 3) absence of psychological conditions, such as
untreated depression.
The role of psychological testing
• Psychological testing allows for:
– evaluation and treatment of comorbid psychiatric
conditions
– assessment of overall mechanisms and support systems for
dealing with pain.
• One study revealed that the predictive value of
psychological testing correlated significantly with
short-term follow-up findings only.
• May involve Oswestry Disability Index, the McGill
Pain Questionnaire (short form), the Roland Morris
Questionnaire, and the Beck Depression Inventory.
Predictive value of psychological
testing
• Many studies have examined the value of
psychological testing in predicting success with SCS
– Daniel et al calculated an 80% accuracy rate using the
MMPI and BDI for predicting success.
– Burchiel et al. found that the BDI score and mania scale on
the MMPI emerged as predictors. Less helpful in a
subsequent study.
– Long et al reported a 33% success rate in unscreened
patients compared with 70% in screened patients.
The trial phase
• Varies from site to site
• After selection, patients then undergo a trial period
of stimulation for 2 to 7 days to assess their response
to the treatment.
– Patients are often asked to record their VAS in a diary
multiple times
– Individuals who achieve >50% or greater pain relief are
candidates for internalization of the device
Neurostimulation Trial
Goals
• The trial provides an opportunity to measure the
effectiveness of neurostimulation without making a
long-term commitment:
– Gauge patient response
– Provides an adjustment period
– Identify therapy parameters
• The goal is at least a 50% reduction in pain without
intolerable side effects
– Patient-specific goals may include less pain
reduction but improved quality of life
Percutaneous Trial
• Most common form of trial
• Performed by:
– “Pain Management”
» Anesthesiologists
» Physiatrists
» Neurologists
– Neurosurgeons
– Orthopedic Surgeons
• Should be performed for trial
unless there are
contraindications
Percutaneous SCS
• Advantages:
– Ease of placement
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Does not require laminotomy
– Decreased pain
– Can screen multiple spinal levels
– Can be placed by non-surgeons
• Disadvantages:
– Cannot always be accomplished
(scar tissue, fusion mass)
– Higher current requirements
– Can be placed by non-surgeons
– Neurosurgeons not traditionally
trained in epidural needle
placement
Percutaneous leads
SCS Leads – surgical and
percutaneous
Needle placement
• Thoracic cord stimulation
– Back and LE
• Entry point in mid-upper lumbar spine
• Tip of lead: T8
• Foot pain:
– Tip of lead T12
– Entry point lower in lumbar spine
• Cervical Stimulation
– Entry point in mid-upper thoracic spine
– Lead tip in cervical spine
Percutaneous Lead Placement
Intraoperative Test Stimulation
A screening system is used during intraoperative test
stimulation:
> Includes an external power source connected to an
implanted lead or percutaneous extension.
> Is used to identify lead location.
> Is used to identify the stimulation parameters –
amplitude, pulse width, and rate – that produce the
paresthesia to provide adequate pain relief.
Complications
• Trial complications
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CSF leak
Increased pain
Hematoma
Infection
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All of the above, plus…
Lead migration
Infection
Malfunction
• Permanent complications
Permanent implant
• Percutaneous or laminectomy
– Percutaneous
• Advantages:
– Easy to perform
– Less invasive
• Disadvantages:
– Higher risk of lead migration
– Higher current requirements
– Laminectomy
• Advantages:
– Low risk of lead migration
– Lower current requirements
– “Better” qualitative sensation
• Disadvantages:
– Requires a surgeon
– More invasive
Trial to permanent
SCS: Results
SCS: Summary
• Better than best medical therapy and
repeat surgery (class I evidence) in cases of:
– Postlaminectomy syndrome
• Effective in cases of:
– Complex regional pain syndrome (RSD)
– Peripheral neuropathic pain
– Ischemic pain of extremities
Thank you