scs – matching therapy to patient

SCS – Matching Therapy to Patient

David L. Caraway, M.D., Ph.D.

CEO, Medical Director

Center for Pain Relief, Tri-State

St. Mary’s Regional Medical Center

Huntington, WV

Neurostimulation Therapy

Spinal Cord Stimulation (SCS)

Implanted medical device that delivers electrical pulses to nerves in the dorsal aspect of the spinal

cord that can interfere with the transmission of pain signals to the

brain and replace them with a more pleasant

sensation called paresthesia.

Neurostimulation is More Effective Than Repeat Surgery

North R, et al. Neurosurgery 2005;56:98-107.

* at least 50% pain relief; would undergo treatment again for same result

Success* at mean 3-year follow-up

0%

10%

20%

30%

40%

50%

Primary Crossover

NeurostimulationRe-operation

47%

12%

43%

0%

(N=45) (N=18)

NS is Most Effective When Considered Early

0%10%20%30%40%50%60%70%80%90%

<2 2-5 5-8 8-11 11-15 >15Time Until Intervention (Yrs)

Succ

ess

Rat

e (%

)

85%78%

42%35%

10% 9%

Kumar K, et al. Neurosurg. 2006;58;481-496.

SELECTION FOR IMPLANTABLE THERAPIES

Questions to explore:When do we offer a trial?What are the indications?What preoperative assessment is appropriate?What constitutes a “successful” trial?What device should be selected?How can device selection be tailored to the

specific patient presentation?

Practice of David Caraway, MD. St. Mary’s Regional Medical CenterHuntington, WV.

Psychological Evaluation

• Consider recommendations and treat if indicated - prior to trial • Ability to understand appropriate expectations• Has patient come to terms with status, expected life span?• Is this someone you are willing to “marry?”• Major active psychosis, current drug addiction, some personality

disorders, cognitive deficits, progressive organic brain disorders, suicidal, homicidal behavior


Patient Beliefs That Support Positive Outcomes

Patient attitudes that can positively affect outcomes should be reinforced by the pain management team

– Pain has multiple components, not purely physical– The patient understands both the benefits and risks of

implanted pain therapy– The patient can affect treatment outcomes– Less than 100% relief is still worthwhile – Family/friends have positive and realistic expectations


GENERAL RULES OF TREATMENT

• SCS IS MORE EFFECTIVE IN NEUROPATHIC OR MIXED PAIN SYNDROMES

• IT DRUG ADMINISTRATION IS MORE EFFECTIVE IN NOCICEPTIVE OR MIXED PAIN SYNDROMES


QUALITY OF PAIN• Easy first choices for STIMULATION

– Burning pain, allodynia in extremities (CRPS I)– Dermatomal, mononeuropathy, CRPS II– “Failed Back Surgery Syndrome” with significant

extremity pain– Trunk (chest wall pain)– Temporarily highly effective diagnostic nerve

blocks


QUALITY OF PAIN• Difficult choices for stimulation

– High dose opioid dependent• Careful trial, monitor opioid requirements, delineation of

expectations– Visceral pain– Compression Fx.– Joint pain– “Mechanical” back pain

Severe pain with flexion and extension, no radicular component, minimal rest pain

While case reports may exist these are not approved indications or lack strong support for clinical success


Spinal Cord Stimulation

• Mechanism of action is complex and not fully elucidated

• Probably related to large fiber stimulation (gate control theory) inhibiting pain transmission, GABA, SEROTONIN, SUBSTANCE P and other transmitters involved

• Point is that it often works• Trial to determine efficacy


SUCCESSFUL TRIAL

• Stimulation covers area of pain• Stimulation is pleasant• Treatment objective attained

– Improved function– Improved pain control by at least 50% ?– Improved vascular studies– Improved physical exam


Trial Considerations • Tunnel at the time

of the trial-Easily connected if trial is a success-Must return to the O.R if trial is unsuccessful-Contamination

• Totally Percutaneous-Can place in fluoroscopy suite-Shared approach to implantation-Must once again position lead in O.R.

Matching Devices to Patients

Key Considerations:• Underlying disease process• Pain pattern and location• Power requirements for optimal stimulation• Programming capabilities• Lead choices • Cognitive ability


Targets • C2 to C4—shoulder to hand

• C4 to C7—forearm to hand

• C7 to T1—anterior shoulder

• T2 —anterior chest wall• T5 to T6—abdomen• T7 to T9—back• T10 to T12—limb• L1—pelvis• L1—foot

Electrode Type

• Percutaneous Lead with Cylindrical Electrode– Omni-directional electrical field– Variety of configurations

• Surgical Lead with Plate Electrode– Uni-directional electrical field– More efficient (40%)– May minimize stimulating painful fibers in

ligamentum flavum

Percutaneous Leads

• Cylindrical style• Minimal or no sedation• Trial and implant arrays are

the same• Less invasive• Flexible lead positioning• More prone to migration1

• Perc unidirectional, electrodes

1Villavicenio AT, Leveque JC, Rubin L, et al. Laminectomy versus percutaneous electrode placement for spinal cord stimulation. Neurosurgery. 2000;46(2):399-405.

Practice of David L. Caraway, MD, PhD. Center for Pain Relief at St. Mary’s, Huntington, WV.

Surgical Leads

• Unidirectional, insulated• Direct Vision• Placed via incision

(laminectomy)• Stable array• More invasive• Lead fracture

Programming—Goals

1. Coverage — generate stimulation field to create paresthesia coverage of painful areas2. Precision — avoid stimulating untargeted sites that create painful sensations or extraneous paresthesia3. Effectiveness — create paresthesia that is effective and provides maximum pain relief4. Efficiency — create programs that maximize pain relief while minimizing power consumption (battery drain)

THE CATHODE DRIVES THE CURRENT

THE ANODE DISPERSES THECURRENT

POLARITY

+ -

+ - -

Electronic Repositioning for Lead Migration

Programming Cannot Overcome . . . • Out of position leads

1. Poor placement location2. Leads that have migrated substantially

• Selection of wrong system1. Inappropriate number or spacing of electrodes —

reduced targeting flexibility and electronic repositioning capabilities for lead migration

2. Inadequate power outputs — cannot activate necessary electrodes or provide sustainable power to optimize pain relief

3. Programming limitation — programmability to match complex pain patterns and patient needs

Effect of postural changes on stimulation

“We found posture to have a significant effect on the charge per pulse when electrode lead are implanted in the thoracic region.”

Cameron and Alo, 1998

“Assuming that patients will (as most do) use their stimulators in a variety of body positions, they will require some method to adjust amplitude frequently throughout the day.”

Olin et al, 1998

“Therefore, to maintain a constant or nearly constant electric field at the level of neural substrate and avoid the potential consequence of postural changes, the amplitude should be varied with each change in posture.”

Abejon and Feler, 2007

Cameron T, Alo KM. Neuromodulation, 1998; Olin JC, et al. Neuromodulation,1998; Abejon D, Feler CA. Pain Physician 2007

Amplitude changes not related to Impedance Changes

• Statistically significant differences in impedance changes have not been found with respect to posture1

• Positional changes can result in spinal cord movement as much as 3 mm2

• Overall patient stimulation comfort correlates to proximity of the cord to the electrodes, not impedance1Constant

• Constant Voltage and Constant Current are functionally equivalent and are not determinant in the outcome of the therapy

1 Abejon D, Feler CA. Pain Physician, 20072 Holsheimer J, et al, Am J Neurol, 1994.

Device Capabilities

• Stimulation parameters– Threshold amplitudes– Array complexity

• Number of expected active cathodes• Number of programs required• Ability of patient to understand and manage their

stimulator– Rechargeability– Program adjustments at home

Complex lead arrangements

d-CSF varies by level DRs have lower threshold than DCs

Science: Anatomical Review

(15 µm

(12 µm)

1

Source: Holsheimer J. and Barolat G. Spinal Geometry and Paresthesia Coverage in Spinal Cord Stimulation. Neuromodulation; Volume 1, Number 3, 1998: 129-136.

Modeling Neuron Recruitment

1. Volume conductor modelAnatomical and electrical properties of spinal cord

2. Model of myelinated nerve fibersActivation of DC & DR fibers

“A finite difference method is applied to discretize the governing Laplace equation. The resulting set of linear equations is solved using a Red-Black Gauss-Seidel iteration with variable over-relaxation.”

Holsheimer and Wesselink, 1997

Science: Potential Solutions

Can this be reversed?

Source: Holsheimer J. and Barolat G. Spinal Geometry and Paresthesia Coverage in Spinal Cord Stimulation. Neuromodulation; Volume 1, Number 3, 1998: 129-136.

Science: Electrical Review• “In a transverse tripolar

simulation it is less likely that motor reflex loops will be activated because the stimulation is more confined to the dorsal column.”

Struijk & Holsheimer. Med. & Biol Eng & Computing. 1996.

+ +-

Science: Potential Solutions

Single Midline Lead

Science: Electrical ReviewTransverse Tripolar Array

“In a transverse tripolar simulation it is less likely that motor reflex loops will be activated because the stimulation is more confined to the dorsal column.”Source: Struijk & Holsheimer. Transverse tripolar spinal cord stimulation: theoretical performance of a dual channel system. Med. & Biol Eng & Computing. 1996.

Three Lead Configurations – Effect of midline contact spacing

The cost of improved recruitment ratio is a significantly higher energy requirement.

Chart from Mekhail NA, Aeschbach A, Stanton-Hicks M. Cost Benefit Analysis of Neurostimulation for Chronic Pain. Clin J Pain. 2004;20:462-468.

Chronic Pain Treatment Continuum 2009

THE END

THANKYOU

scs – matching therapy to patient

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