Spinal Cord, Peripheral Nerve, and Peripheral Nerve Field by elfphabet4

VIEWS: 255 PAGES: 6

									123                            Spinal Cord, Peripheral Nerve, and
Page 1
                   Peripheral Nerve Field Stimulation for the Treatment of Pain

             Timothy R. Deer, M.D.                                               Charleston, West Virginia
INTRODUCTION:
         Stimulation of the nervous system is an option to treat many medical conditions including cardiac
arrhythmias, tremor, and depression. This section will focus on the neuromodulation of the nervous system to
change neural transmission and perception relating to pain. Electrical current can be applied at the level of the brain,
spinal cord (SCS), peripheral nerves (PNS), and peripheral nerve fields (PNFS).

HISTORY OF ELECTRICAL CURRENT FOR PAIN TREATMENT:
           The first recorded use of electrical current to treat pain was in 15 AD when the torpedo fish was discovered
to treat the symptoms of gout in a patient exposed to the eel like creature. Gilbert, a 17th century scientist, advanced
the use of electricity when he published the use of lodestone, which is a piece of magnetic iron ore possessing
polarity like a magnetic needle, as a treatment for headaches, mental disorders and marital infidelity. In 1745,
Musschenbroek described the ability to store electricity in a capacitance device called a Leyden jar. This jar was
used by Jallabert to stimulate muscle and increase blood flow. Benjamin Franklin advanced these ideas by using
electrical current to treat many painful disorders such as headaches, arthritis and back pain. Franklin concluded that
the use of high voltage electricity caused more pain than it relieved. The use of electricity in humans was then out
of favor until several decades later when Volta explained the chemical interactions that occurred in the body with
low voltage electrical exposure. This revelation led to the work that is still relevant in modern day patient care with
low voltage current.

          These concepts were studied by Ampere, Faraday, and Clarke, but the use of current to treat pain was still
limited and poorly understood. In 1840, the work of Guillaume Duchenne took the use of electricity to the next
level in human application. Duchenne used electropuncture, or application of electricity to small needles inserted
directly into muscles to observe that closing of the circuit caused contraction of specific muscles allowing for exact
mapping of muscle function. Duchenne summarized his thoughts in the book “De L’electrisation Localise” where
he described direct muscle stimulation and indirect nerve stimulation. This work led to the development of early
prostheses that used surface electrodes to move the body part. The first successful use of these same concepts for
pain did not occur until over one hundred years later when Norman Shealy described the use of Spinal Cord
Stimulation for the treatment of pain. In 1968, FDA approval was achieved to treat pain with these devices. The
devices were crude bipolar devices with little ability to be individualized to meet patient needs. In the next four
decades major advances have been made and the use of stimulation is now entering an exciting time in its history in
regard to patient application, technology and science.

SPINAL CORD STIMULATION (SCS):

SCIENTIFIC PRINCIPLE:
          Spinal cord stimulation involves the placement of a lead over a neural target in the spine achieved by
epidural placement. Once the lead is targeted to the appropriate fibers a power source is attached to deliver energy
to the leads to produce an electrical field. By using a programmable generator the amplitude, rate, frequency and
shape of the electrical field can be manipulated to create pain relief. The mechanism of neural effect has been
theorized to change the balance of inhibitory to excitatory fiber activity by the gate control process, by manipulating
the number and position of cathodes and anodes on the lead.

INDICATIONS FOR STIMULATION:
         In the United States, the Food and Drug Administration has approved this therapy for the treatment of
moderate to severe pain in the trunk or limbs. The specific indications for which these devices are most commonly
used have been well defined. The most common indication for spinal cord stimulation is failed back surgery
syndrome. Other common reasons patients undergo these surgeries include cervical and lumbar radiculitis, complex
regional pain syndrome, peripheral neuropathies, post herpetic neuralgia, ischemic limb pain, angina, pelvic pain
and other neuropathic and visceral pain syndromes.
123
Page 2
PATIENT SELECTION:
         Patients are appropriate for spinal cord stimulation when they have failed more conservative treatment or
when these measures are not acceptable. The patient should be mentally stable, have no untreated drug addiction,
have no untreated clotting disorders, and have no local infection at the procedure site or untreated systemic
infections. The patient should undergo a trial of stimulation and significant relief during that time period. The trial
can vary in length from a few hours to several weeks with most lasting three to seven days.

PAIN TREATMENT ALGORITHM:
         In the past, spinal cord stimulation was relegated to an end of care option for those that have failed all other
options. Several factors have changed this antiquated thinking. These changes include the simplification of
stimulation trialing which now can be done via a percutaneous skin puncture with no incisions, monitored care and
same day discharge. Other major factors include a recent randomized study by North that has shown that spinal
cord stimulation is superior to a second back surgery in regard to pain relief, satisfaction, and need to have the other
therapy. Recent analyses of long acting opioids for chronic non-cancer pain have shown poor long term outcomes
regarding pain relief. These factors coupled with increasing national trends of addiction and abuse has led many
clinicians to choose spinal cord stimulation as an earlier option. Recently, a consensus group of experts met to
review the evidence for use of these technologies. The recommendation was to advance stimulation to an earlier
position in the algorithm for pain of spinal origin. Figure one shows the antiquated algorithm, and Figure two, the
algorithm for 2007 and the near future.

         As the figures indicate the use of stimulation should be considered much earlier in those with spinal related
pain syndromes. The device should be used prior to the second or subsequent surgeries unless neurological
compromise is a risk. Spinal cord stimulation should be an option instead of the initial spine surgery when surgery
isn’t imminent or emergent. Chronic long acting opioids have been recently questioned as to efficacy in improving
function or long term pain relief.

Figure 1. Old Continuum



                                                            The old continuum placed SCS at the end of the algorithm
                                                            equal with intrathecal drug delivery and Neuroablative
                                                            surgeries. This placement was based on the initial approval
                                                            of SCS when it always involved a surgical laminotomy.
                                                            Recent percutaneous techniques have made these therapies
                                                            much less invasive.




Figure 2. New Continuum


                                                              The new continuum advances SCS to a more
                                                              appropriate place in the algorithm. SCS should
                                                              be considered after nerve blocks, physical
                                                              therapy and other conservative measures fail.
                                                              Psychological evaluation should occur prior to
                                                              permanent SCS placement and spine surgery
                                                              should be considered if loss of neurological
                                                              function is a risk.
123
Page 3
SPINAL CORD STIMULATION: THE PROCEDURE
GENERAL PRINCIPLES:
          The patient should be prepped and draped widely prior to starting the procedure. The prep solution should
be known to kill the common pathogens of your institution. Intravenous antibiotics should be given prior to
incision. In most settings, the antibiotic of choice is a third generation cephalosporin with broad coverage including
the cerebral spinal fluid. In high risk patients such as those with immunosuppression the use of vancomycin is often
recommended. Intraoperative antibiotic irrigation commonly includes bacitracin or kanamycin. Postoperative
antibiotics are controversial, but most clinicians prefer cephalosporins. Positioning should optimize spinal exposure,
provide comfort to the patient and maintain sterility. The patient can be sedated, but should remain conversant and
responsive to report paresthesias.

NEEDLE PLACEMENT:
         The angle of the needle is important to improve the ability to drive the lead to the proper neural target. An
angle of 30 degrees is ideal for epidural entry. Steeper angles increase the risk of wet tap and nerve injury. A
paramedian approach is preferred, with a skin entry site two levels below the desired entry space. The needle entry
should be two to three levels below the final lead target. In the cervical spine the needle entry at or below the C7-T1
space.

LEAD PLACEMENT:
         The lead should be driven to the posterior epidural space at the desired level of stimulation. If the patient
reports pain or paresthesia during the placement the lead should be retracted and repositioned. The lead can be
guided using a straight or curved stylet. Fluoroscopic guidance should show good placement on both antero-
posterior and lateral views.

LEAD TARGET:
          The physician should understand the target for the led to achieve proper stimulation. Table one provides
general targets for spinal cord stimulation.

Table 1. Lead Placement for Anatomical Stimulation

 Region        Position              Target
 Cervical     C2 Lateral    Mandible, Neck
              C2-3          Shoulder
              C4-6          Arm
              C7            Anterior Shoulder, Chest

 Thoracic     T1-3          Angina
              T4-6          Visceral Abdomen
              T7-9          Axial Back
              T10           Knee, Hip
              T11-12        Leg

 Lumbar       L1            Foot
              L5-S1         Foot
              Nerve Root

  Sacral      S2-4          Pelvis, Rectum, Perineum



LEAD PROGRAMMING:
         Current is driven into the cord based on the presence of a cathode. The shape of the effect of stimulation
on the spinal cord is based on the cathode and anode array, and the number of cathodes and anodes present.
123
Page 4
LEAD ANCHORING:
           Once the lead is in good position it should be secured to the tissue to avoid later displacement. The desired
tissue is ligament and fascia. Prior to securing the anchor all adipose tissue should be débrided. Non-absorbable
suture is then used to attach the lead to the spine with an appropriate silastic anchor. Once the lead is anchored a
strain relief loop should be placed in the wound. The best way to anchor the lead has been debated. Many modern
anchors have mechanical components that assist with keeping the lead in position. The highest risks of migration
occur in the first six weeks post implant.

POCKET FORMATION:
          The position of the pocket is based on patient preference and body habitus. Options include the buttock,
abdominal wall, flank, and chest wall. The depth of the pocket should be appropriate to avoid skin erosion, but
should also assure good communication with telemetry. When creating a pocket the physician should consider the
belt line and bony landmarks.

COMPLICATIONS OF SCS:
         The most common complications of spinal cord stimulation include lead migration, superficial infection,
and connection abnormalities, wet tap, and nerve irritation. More serious problems include epidural hematoma,
epidural abscess, paraplegia, and death. The number of complications can be reduced by sterile technique,
preoperative assessment, and proper selection.

PERIPHERAL NERVE STIMULATION (PNS) AND PERIPHERAL NERVE FIELD STIMULATION
(PNFS)

SCIENTIFIC PRINCIPLE:
         In some disease states the nerve that is involved in the generation of pain is easily stimulated in the
periphery. This may be performed by placing the lead directly over the nerve or by stimulating the fibers of the
nerve as it courses in the tissue. The theory of this technique is that the device can effect the transmission of pain
signals via A delta and C fibers.

PNS:
          Peripheral nerve stimulation is performed by identifying the nerve involved in the pain transmission and
directly applying current to the structure. In order to perform PNS, the surgeon has to dissect and identify the nerve.
At this point a fascial graft is placed over the nerve to insulate the fibers from direct stimulation. This technique is
technically challenging and fraught with problems. In most clinical disease states the use on PNFS has become
more common.

PNFS:
          The occipital nerve, ilioinguinal nerve, cluneal nerve, and intercostal nerves are receptive to stimulation of
their peripheral fibers in lieu of stimulating the entire nerve.

          In order to perform this technique, the nerve field is mapped out by exam, the tissue is prepped and draped,
local anesthesia is applied and the needle is placed just below the dermis in the subcutaneous tissue. If the needle is
too superficial the lead can erode. If the lead is too deep, the nerve fibers are missed. Table two shows the potential
targets for peripheral nerve stimulation.

COMPLICATIONS OF PNS AND PFNS:
         The risks of these techniques are limited. They include cellulitis, peripheral nerve injury and mechanical
dysfunction of the leads and generator.
123
Page 5
Table 2. Targets for PNS and PNFS Placement

                        Disease                                              Nerve Target
 Occipital Neuralgia                                     C2 Fibers at the Occiput
 Neuritis of the Face                                    Supraorbital, Infraorbital
                                                         Temporal-Auricular, Trigeminal
 Upper Extremity Pain                                    Median, Ulnar, Radial, Axillary
 Pain of Torso                                           Intercostal and Thoracoabdominal

 Pain of Pelvis                                          Ilioinguinal, Iliohypogastric
 Pain of Lower Extremity                                 Common Peroneal, Superficial
                                                         Peroneal, Lateral Femoral Cutaneus, Tibial,
                                                         Saphenous


NEUROMODULATION AS A DISEASE MANAGEMENT STRATEGY:
         Many physicians and patients are excited about the use of neuromodulation to change patient’s function
and improve the quality of life. Many uses of this technology are already clinically available, but many more
therapies are on the horizon. Figure three below illustrates the current state of these technologies. Targets include
the motor cortex, thalamus, peripheral nerves, cranial nerves and new areas of the spinal cord.

Figure 3. Approved and Future Neuromodulation Indications
123
Page 6
SUGGESGTED READING:


         1. North R, Kidd D, Farraokhi F, Piantadosi S. Spinal cord stimulation versus repeated lumbosacral spine
             surgery for chronic pain: a randomized, controlled trial. Neurosurgery. 2005;56(1):98-106.


         2. Mekhail N, Aeshbach A, Stanton-Hicks M. Cost Benefit analysis of neurostimulation for chronic pain.
             Clin J Pain. 2004 Nov-Dec:20(6): 462-8.


         3. Taylor R, Van Buyten J, Buscher E. Spinal cord stimulation for complex regional pain syndrome: a
             systematic review of the clinical and cost-effectiveness literature and assessment of prognostic factors.
             Eur J Pain. 2006 Feb;10(2):91-101



         4. Melvin E, Jordan F, Weiner R, Primm D. Using peripheral stimulation to reduce the pain of c2-
             mediated occipital headaches: a preliminary report. Pain Physician. 2007 May;10(3):453-60.


         5. Levy R. Deep brain stimulation for the treatment of intractable pain. Neurosurg Clin N Am. 2003
             Jul;14(3):389-99, vi.


         6. Deer T. Current and future trends in spinal cord stimulation for chronic pain. Current pain and
             headache reports 2001, (5): 503-509.


         7. Deer T, Levy R, Feler C, Krames E, Hassenbusch S, Racz G, Kim C, Bowman R, Caraway D, Staats
             P, Raushbaum R, Burton A, Sitzman T, et al. A consensus of the use of Spinal Cord Stimulation for
             the treatment of pain in pain of spinal origin. Consensus conference on spinal cord stimulation.
             December 2006. Dallas, Texas.

								
To top