Lecture 12: Neuromodulation for Chronic Pain

Question 1

Chronic pain
* define
* what is it caused by

Answer 1

persistent or intermittent pain lasting 3 months or longer. Normal activities can become severely restricted or even impossible

• an ongoing cause such as arthritis, cancer or infection OR
• an initial injury that has long since healed.

Question 2

What are the physical effects of pain

Answer 2

• increased heart rate and blood pressure, increased blood sugar, decreased digestive activity, reduced blood flow

Question 3

What are the psychosocial effects of pain

Answer 3

fear, anxiety,
interference with work, decreased self esteem, problematic relationships

Question 4

What are some possible sources for back pain

Answer 4

• IV discs
• facet joints
• vertebrae
• neural structures
• muscles
• ligaments
• fascia

Question 5

Constitutional symptom

Answer 5

A symptom or manifestation
indicating a systemic or general effect of a disease
and that may affect the
general well-being or status
of an individual.

Question 6

Cauda Equina Syndrome (CES)
* describe it
* what can it progress to
* what is it an absolute indication for
* when should they be treated?

Answer 6

• low back pain, bilateral/unilateral sciatica, saddle anesthesia, motor weakness
• paraplegia, permanent bowel or bladder dysfunction
• absolute indication for surgical treatment of lumbar disc disease
• surgery within 48 hours

Question 7

List some possible chronic back pain medications, injections, and non-invasive treatments

Answer 7

• NSAIDs
  
  • Watch out for GI renal defects
• Opioids
• Muscle relaxants
  
  • Sedation side effect
• Epidural steroid injection (acts as an inflammatory to hopefully decompresses nerve) (requires fluoroscopy for guidance); can dissolve tissues you don’t want it to
• physical therapy

Question 8

How long does an epidural steroid injection last?

Answer 8

about 6 months

Question 9

Straight leg raise
what is a positive sign
+ sign means what
whats this tests importance

Answer 9

elevation of the leg at 30-70 deg of hip flexion reproduces pain and paresthesia in the extremity

tension on the L5-S1 nerve root

predicts good candidates fro back surgery

Question 10

laminotomy and discectomy
* what is it
* what does it treat

Answer 10

disc herniation

Question 11

Spinal stenosis
* define it

Answer 11

is a narrowing of the spinal canal, compressing the nerves traveling through the lower back into the legs

Question 12

What are the strongest predictors of outcome of surgery for lumbar spinal stenosis

Answer 12

• comorbid medical conditions (obesity (more time under anesthesia), hypertension, hyperlipidemia)
• smoking, multilevel spinal stenosis, and household income are smaller predictors

Question 13

What are the two types of chronic pain

Answer 13

1. Nociceptive Pain (somatic/visceral)
2. neuropathic

Question 14

Describe nociceptive pain
* caused by
* described as
* responsive to
* sources

Answer 14

• Is mediated by nociceptors widely distributed in cutaneous tissue, bone,
  muscle, connective tissue, vessels, and viscera.
• Is caused by tissue trauma or mechanical, thermal or chemical excitation.
• Described as dull, aching, throbbing pain that is sometimes sharp.
• is often responsive to opioid therapies, delivered orally, transdermally,
  parenterally or spinally.

Sources:
* Injured tissues
* Bone (e.g., from a fracture, bone metastases)
* Cancer

Question 15

Describe neuropathic pain
* describe the feeling
* what is it responsive to

Answer 15

• Neurological damage causing pathologic changes in neuro-functional
  relationships within the peripheral or central nervous system, such as
  
  • Central sensitization or “wind-up”; brain responds more strongly than normal
  • Abnormal sympathetic-somatic nervous system interactions
  • Abnormal activation of NMDA receptors
• Burning, tingling, shooting, electric-like or lightning-like pain.
• May be opioid resistant or require high opioid doses to achieve relief.

Question 16

• what conditions involve neuropathic pain

Answer 16

• Radiculopathies – spinal root compression
• Neuropathies – diabetes, toxins, nerve compression
• Neuralgias – pain from damaged or irritated nerves
• Failed back surgery syndrome – pain after spine surgery
• Complex regional pain syndrome – after an arm or a leg injury
• Arachnoiditis – inflammation caused by infection, injury,
  or chronic compression of the spinal cord
• neuromas

Question 17

describe central sensitization
* what causes it?

Answer 17

• a phenomenon of synaptic plasticity and increased
  neuronal responsiveness in central pain pathways after painful insults
• Neuroinflammation in peripheral and central nervous systems a

Question 18

chronic pain is maintained in part by __________

Answer 18

central sensitization

Question 19

A feature of neuroinflammation is the activation of glial cells such as _________ in the spinal cord and brain, causing release of _______

Answer 19

microglia and astrocytes

proinflammatory cytokines and chemokines.

Question 20

What is the role of central cytokines and chemokines

Answer 20

powerful neuromodulators that play a role in inducing hyperalgesia and allodynia (pain from stimuli that don’t
usually cause pain).

Question 21

Sustained increase of cytokines and chemokines in the CNS promotes what?

• what illnesses can it promote?

Answer 21

chronic widespread pain that affects multiple body sites

post-herpetic neuralgia, phantom limb pain, painful diabetic
neuropathy and complex regional pain syndrome.

Question 22

What are the two discussed Implanted Neuromodulation Therapies for Pain

Answer 22

• intrathecal drug delivery
• neurostimulation

Question 23

define: neuromodulation

Answer 23

a normal property of the nervous system that
regulates or modifies electrical impulses flowing through neural tissues by
enhancing, inhibiting, extending, or shortening them

At the cellular level, it may involve modulation of the effects of specific receptors
or ion channels on neuronal excitability.

Question 24

Describe interventional neuromodulation
* describe the two types

Answer 24

a nondestructive and reversible therapy. It includes the use of implanted or nonimplanted

• chemical neuromodulation by infusion of chemical agents directly to the
  central nervous system
• electrical stimulation systems that stimulate peripheral nerves, dorsal
  root ganglia, the spinal cord or the brain

Question 25

Describe intrathecal drug delivery for pain

Answer 25

The intrathecal drug delivery system
consists of an intrathecal drug infusion
pump and an intrathecal catheter, which
are both fully implanted.

The catheter is placed in the intrathecal
space of the spine and connected to the
implanted pump that releases prescribed
amounts of medication to the
cerebrospinal fluid.

Small doses of medication (like morphine) are directly brought to the cerebrospinal fluid

Question 26

What is the intrathecal to oral morphine dorse conversion

Answer 26

1:300

The lower dose results in reduced systemic effects from the drug.

Question 27

What are the risks of intrathecal drug delivery

Answer 27

The risks of intrathecal drug delivery
include surgery-related risks such as
bleeding, infection, catheter and pump
complications, and drug overdose (delivery of refill outside of the pump) or
other adverse events.

Question 28

List the criteria for determining if intrathecal drug delivery is appropriate for patient

Answer 28

• More conservative therapies have failed to adequately help the pain.
• An observable pathology exists that is associated with the pain.
• Further traditional surgical intervention is not indicated.
• No serious untreated drug habituation for the pain condition exists.
• Psychological evaluation and clearance for implantation received.
• No medical issues exist that could present complications with surgery.
• In general, IDD is indicated for:
• Chronic, intractable pain of malignant or non-malignant origin
• Nociceptive or mixed pain

Question 29

A neurostimulation system consists of:

Answer 29

• one or more stimulating leads that deliver electrical
  stimulation to the spinal cord or peripheral nerve
• an extension wire that conducts electrical pulses from the power source to the lead, and
• a power source that generates the electrical pulses.
• screener: temporary external power sources
  used during intraoperative test stimulation and the
  screening test period. A temporary extension attached to the lead is connected to a screening cable which is
  connected to the screener
• physician programmer: computers
  used with the totally implanted system that
  allow the clinician and patient to noninvasively set parameters and modes
• control magnet

Question 30

What are the two types of implanted neurostimulation systems

Answer 30

1. Totally implanted
   * the leads and the power source (battery) are surgically implanted
2. Partially implanted
   * the leads and a radio-frequency receiver are implanted
   * the power source is worn externally with an antenna over the receiver (some devices require a lot of power and need to be replaced often)

Question 31

What are the two types of leads used in neurostimulation systems

Answer 31

Percutaneous Leads are either quadripolar (4
electrodes) or octapolar (8 electrodes) with cylindrical
electrode design for delivering stimulation.

Surgical Leads with plate electrodes are at least
quadripolar to create multiple stimulation
combinations and a broad area of paresthesia.

if you arent sure where you want to put the leads exactly in the SCI so you use surgical leads to search

Question 32

What are the two types of power sources used in neurostimulation systems

Answer 32

Internal Battery Power Source:
Totally self-powered neurostimulator
with non-invasive programmability.

Radio-Frequency Coupled Power Source:
Used for patients with high energy requirements.
Includes an implantable receiver and external
transmitter and antenna.

Question 33

What are some external system components for the neurostimulation system

Answer 33

• screener: temporary external power sources
  used during intraoperative test stimulation and the
  screening test period. A temporary extension attached to the lead is connected to a screening cable which is
  connected to the screener
• physician programmer: computers
  used with the totally implanted system that
  allow the clinician and patient to noninvasively set parameters and modes
• Patient Programmers are small hand-held
  units used by patients to adjust their
  stimulation amplitude, rate and pulse width.
  This programmer also turns the neurostimulator ON or OFF.
• Control Magnet is an optional accessory
  used to turn the stimulation ON and OFF as needed.

Question 34

How Neurostimulation Controls Pain

Answer 34

Neurostimulation delivers low voltage electrical stimulation to the spinal cord or
targeted peripheral nerve to block the sensation of pain.

A neurostimulation system implanted in the epidural space stimulates these paininhibiting nerve fibers, masking the sensation of pain with a tingling sensation
(paresthesia)

Conventional Spinal Cord Stimulation involves
programming frequencies most commonly in
the 40–60 Hz range, and produces the
sensation of paresthesia, which must overlap
the area of pain to provide analgesia

Question 35

What is neurostimulation an appropriate treatment for?

Answer 35

• Failed Back Syndrome or low back syndrome or failed back
• Radicular pain syndrome or radiculopathies resulting in pain secondary to
  FBS or herniated disk
• Post-laminectomy pain
• Multiple back operations
• Unsuccessful disk surgery
• Degenerative Disk Disease/herniated disk pain refractory to conservative
  and surgical therapies
• Peripheral causalgia (severe burning pain from injury to a nerve)
• Epidural fibrosis
• Arachnoiditis or lumbar adhesive arachnoiditis
• Complex Regional Pain Syndrome (CRPS), Reflex Sympathetic Dystrophy
  (RSD) or causalgia

Question 36

Gait Control Theory of pain

Answer 36

gate in the spinal cord that controls the flow of noxious pain signals to the brain. The theory suggests that the body can inhibit these pain signals or “close the gate” by activating certain non-noxious nerve fibers in the dorsal horn of the spinal cord

in absence of input from C fibres, a tonically active inhibitory interneuron suppresses pain pathway

With strong pain, C fiber activity stops inhibition of the pathway,
allowing a strong signal to be sent to the brain.

The transmission of Pain can be modulated by
simultaneous somatosensory input.

AB fibre shares the same interneuron. can act on it. (review ur other class’s notes on gate theory)

Question 37

define: referred pain
* what is one theory on referred pain

Answer 37

Pain in internal organs is often sensed on the surface of the body, a sensation known as referred pain.

One theory of referred pain says that nociceptors from several locations converge on a single ascending tract in the spinal cord.
Pain signals from the skin are more common than pain from internal
organs, and the brain associates activation of the pathway with pain
in the skin.

Question 38

Benefits of Neurostimulation

Answer 38

• Improve pain relief (a majority of patients may experience at least
  50 percent reduction in pain)
• Increase activity levels
• Reduce use of narcotic medications
• These results may also lead to reduced hospitalizations and
  surgical procedures, reduced health care costs, greater
  independence, and improved quality of

Question 39

What is the patient selection criteria for spinal cord sitmulation

Answer 39

1. More conservative therapies have failed
2. An observable pathology exists that is concordant with the pain complaint
3. Further surgical intervention is not indicated
4. No serious untreated drug habituation exists
5. Psychological evaluation and clearance for implantation has been obtained
6. No contraindications to implantation exist
7. A screening test has been successful (1st stage in the procedure - implant stimulation electrodes epidurally for the trial screening period of 1-10 days)

Question 40

Describe the Screening Test for Neurostimulation Lead Placement and
Intraoperative Test Stimulation

Answer 40

During intraoperative test stimulation the patient is in a prone position, fully awake
and actively participating in the test stimulation. The physician positions the lead so that the stimulation pattern covers as much of the patient’s pain pattern as possible.

The lead is connected to the
screener (temporary power source)
that is used to set amplitude, pulse
width, rate, and lead selections.
Each lead can be set at +, -, or OFF
which allows for multiple electrode
combinations. At least one electrode
must be positive, and one electrode
must be negative.
The level of the spinal cord where
the negative electrode is located is
the primary stimulation level.

As the lead is positioned and electrode selections are changed, the patient provides
feedback about location and intensity of paresthesia. This give-and-take between
patient, physician, and other members of the team is critical to locating the best
lead position and electrode selections for that patient.
The clinician asks specific questions in relation to specific areas of the body, such as
* Do you feel a tingling sensation?
* Is the sensation covering the pain in this area?
* Is the sensation covering all of your pain?
* What percent of the painful area is covered by the tingling?
* Is the sensation comfortable?
The lead is adjusted so that paresthesia covers the painful area as fully as possible.
When optimal coverage is achieved, an x-ray is taken to document lead tip position.
Temporary lead: Some clinicians choose to implant a lead temporarily for the
screening test. Leads implanted using a temporary implantation protocol with
alternate anchoring techniques are typically removed within 10 days.
After intraoperative test stimulation, the physician places a temporary extension for
a screening test period. The percutaneous extension wire is taped in place, and
sterile dressings are applied. All settings are carefully documented by the clinician.

The screening test period of trial stimulation provides:
* Evaluation of impact of stimulation on the patient’
s pain and daily life.
* A low-cost means of evaluating the effectiveness of the therapy.
* Exclusion of non-responding patients prior to system implantation.
* Identification of lead position and stimulation parameters.
* A method of demonstrating efficacy to third-party payers and review bodies.
The screening test period is an opportunity for the patient to develop an
understanding of the technology and realistic expectations of the therapy.
During this time the patient is carefully educated and encouraged to try
different parameter settings to optimize and fully “test” neurostimulation.
At the end of the screening test period, patients return to the physician’s office
for an assessment of their experience with the therapy.
If the patient does not respond positively to neurostimulation during the
screening test period, the lead is removed. If the patient responds positively to
a neurostimulation system during the test period and the pain relief achieved
with stimulation is 50% or greater during activities that normally elicit pain, a
complete neurostimulation system is implanted.

Question 41

Describe the neurosystem implant procedure

Question 42

Describe the surgical lead paddle implant procedure

Question 43

Describe the postoperative care after neurostimulation system implantation

Answer 43

• management of complications
• patient education
• care of operative site
• system reprogramming (if necessary)
• prophylactic antibiotics
• advised to limit activtiies to reduce risk of lead movement and subsequent loss of stimulation

Question 44

What are possible postoperative complications following neurostimulation implant?

Answer 44

• surgical complications (infections, hematoma, epidural hemorrhage, CSF leakage, paralysis, pain, discomfort, seroma at the neurostimulator or receiving site)
• system complications
  (electrical leakage, lead or neurostimulator erosion/migration, connection problem, wire breakage, short circuit)
• short circuits drain batteries, can cause heat, can cause internal burns
• patient may experience loss of pain relief, loss of stimulation, undesirable change in stimulation can be described as uncomfortable (jolting/shocking), radicular chest wall stimulation, allergic or immune response

Question 45

What patients are more likely to have post surgical infections?

Answer 45

Patients who have
poor nutritional status, are small and/or thin, or have generally poor health are
at greater risk for post-surgical infections.

Question 46

Describe dorsal root ganglion stimulation for pain
* what is this a possible treatment for?
* what makes this treatment better than other spinal cord stimulators?

Answer 46

• stimulate dorsal root ganglion (dorsal root afferents)
• chronic intractable leg pain (difficult to target anatomy such as back and foot);
• limits uncomfortable postural effects typically experienced with other SC stimulators (leads are more stable with movement)

Question 47

High-Frequency Spinal Cord Stimulation for Pain
* What is the frequency
* How do they differ from traditional stimulation (3)
* what is the advantage of high frequency vs low
* how does it block pain?

Answer 47

• 10kHz
  1) the two leads are sited solely anatomically—in the midline spanning T8 to T11;
  2) concordant paresthesia mapping is not performed at any time
  3) there is no need to lighten sedation for paresthesia testing
• Paresthesia-free pain. paresthesia can be uncomfortable or intolerable to some patients. can allow for patient to drive (since you’re not allowed to drive with paresthesia-based stimulation
• selectively activates inhibitory interneurons in the dorsal horn (DH)
  at low stimulation intensities, which do not activate the dorsal column fibers. This ostensibly
  leads to suppression of hyperexcitable wide dynamic range neurons (WDR), which are sensitized and hyperactive in chronic pain states

Low-frequency SCS works by activating large-diameter A fibers in the lateral discriminatory
pathway (pain location, intensity, quality) at the dorsal column (DC), creating paresthesiabased stimulation at lower-frequencies (30–120 Hz), high-amplitude (3.5–8.5 mA), and
longer-duration/pulse-width (100–500 microsec).

review slide 55