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

Explain the differences between acute vs. chronic back pain, and what you should do to assess each.

Answer 2

Chronic pain is defined as pain that lasts three months or longer. This pain may be persistent or intermittent

Acute pain is back pain lasting for less than 3 months

To assess
- ask for patient history (including when it started, previous injuries or illnesses, symptoms, what interventions they have tried)
- perform physical examination on patient
- assess the impact on daily life including impact on ADL, IADL, relationships, and patient wellbeing

Question 3

What are the physiological effects of pain

Answer 3

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

Question 4

What are the psychosocial effects of pain

Answer 4

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

Question 5

What are some possible sources for back pain

Answer 5

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

Question 6

Constitutional symptom

Answer 6

non-specific symptoms that indicate a generalized illness or disease

may affect the general wellbeing or status of an individual.

examples: weight loss, fever, headache, fatigue

Question 7

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

Answer 7

• 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 8

List the types of therapies available to treat pain in the order that they should be used.

Answer 8

Most conservative to least conservative:
* NSAIDs such as ibuprofen and naproxen (watch out for GI damage)
* physical therapy
* Opioids
* Muscle relaxants (careful of sedative 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
* corrective surgery (laminectomy and discectomy for disc herniation)
* implanted neuromodulation therapies (intrathecal drug delivery and neurostimulation)

Question 9

How long does an epidural steroid injection last?

Answer 9

about 6 months

Question 10

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

Answer 10

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 for back surgery

Question 11

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

Answer 11

disc herniation

Question 12

Spinal stenosis
* define it

Answer 12

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

Question 13

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

Answer 13

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

Question 14

What are the two types of chronic pain

Answer 14

1. Nociceptive Pain (somatic/visceral): arises from the activation of nociceptors, which are specialized sensory receptors located throughout the body
2. neuropathic: neurological damage that leads to pathological changes in the way nerves function in either the peripheral or central nervous systems.

Question 15

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

Answer 15

• 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 16

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

Answer 16

• 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 17

• what conditions involve neuropathic pain

Answer 17

• 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 18

Describe central sensitization

When and how is central sensitization, or “windup”, thought to develop?

Answer 18

Increased neuronal responsiveness in the central pain pathways due to synpatic plasticity after neuronal damage. Chronic pain is thought to be maintained in part by central sensitization.

Neuroinflammation, or inflammation in the peripheral and central nervous systems, appears to drive central sensitization.
● Activates glial cells (like microglia and astrocytes) in the brain and spinal cord
● leads to the release of proinflammatory cytokines and chemokines
● Cytokines and chemokines in the central nervous system are powerful neuromodulators that can induce hyperalgesia (increased sensitivity to pain) and allodynia (pain from stimuli that do not usually cause pain).
● Sustained increases in these substances in the CNS can promote chronic widespread pain that affects multiple body sites

Question 19

Sustained increase of cytokines and chemokines in the CNS can possibly promote what kind of illnesses (as seen with central sensitization) ?

Answer 19

chronic widespread pain that affects multiple body sites

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

Question 20

What are the two discussed Implanted Neuromodulation Therapies for Pain

Answer 20

• intrathecal drug delivery
• neurostimulation

Question 21

define: neuromodulation
at the cellular level what could this involve

Answer 21

regulation or modification of electrical impulses flowing through the 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 22

What is interventional neuromodulation.
* describe the two types

Answer 22

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 (intrathecal baclofen)
• electrical stimulation systems that stimulate peripheral nerves, dorsal root ganglia, the spinal cord or the brain

Question 23

Describe intrathecal drug delivery for pain

Answer 23

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 24

What is the intrathecal to oral morphine dose conversion

Answer 24

1:300

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

Question 25

What are the risks of intrathecal drug delivery

Answer 25

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 26

List the criteria for determining if intrathecal drug delivery is appropriate for patient
* what type of pain is intrathecal baclofen appropriate for?

Answer 26

• More conservative therapies have failed to adequately help the pain.
• An observable pathology exists that is associated with the pain.
• nociceptive or mixed pain - not neuropathic
• 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 27

Describe the similarities and the differences between implanted chemical vs. electrical neuromodulation systems to treat chronic pain.
* mechanism
* component
* benefits
* risks
* patient selection criteria

Answer 27

mechanism:
* chemical: Delivers pain medication directly to the cerebrospinal fluid, blocking pain signals at the spinal cord.
* electrical: Disrupts pain signals by delivering low-voltage electrical stimulation to the spinal cord or peripheral nerves.

components:
* chemical: Implanted pump and Intrathecal catheter
* electrical: Stimulating leads; Extension wire; Power source

benefits
* chemical: targeted drug delivery with reduced systemic side effects; lower medication doses required
* electrical: pain relief through paresthesia, tingling sensation; reduced reliance on medication

risks
* chemical: pump and catheter complications; overdose; infection; bleeding
* electrical: lead migration, connection problems, uncomfortable sensation that may not allow for driving

patient selection criteria
* similar except electrical needs to pass screening test

Question 28

A neurostimulation system consists of (6)

Answer 28

• 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 29

What are the two types of implanted neurostimulation systems

Answer 29

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 30

What are the two types of leads used in neurostimulation systems

Answer 30

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 31

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

How do neurostimulation systems slightly differ depending on power source?

Answer 31

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 32

What are some external system components for the neurostimulation system

Answer 32

• 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 33

How does neurostimluation control pain?

What is the programming frequency for conventional spinal cord stimulation

Answer 33

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

Normally (in absence of pain), inhibitory interneuron is tonically activated, causing supression of the pain pathway.

During strong pain, c fibres are activated strongly and inhibits inhibitory interneuron, allowing signals to be sent up the ascending pain pathway.

Ab are activated by non-noxious stimuli, such as light touch, pressure, and hair movement
* stimulation of Aβ fiber causes activation of inhibitory interneuron that supresses ascending pain pathway.

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 34

What is neurostimulation an appropriate treatment for?

Answer 34

• 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 35

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

Answer 35

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 36

Benefits of Neurostimulation for chronic pain

Answer 36

• 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 37

What is the patient selection criteria for spinal cord sitmulation

Answer 37

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 38

With high-frequency spinal cord stimulation, why is it that tingling sensations don’t arise? What is thought to happen, that helps relieve the sensation of chronic pain?

Answer 38

different stimulation pattern selectively activate inhibitory interneurons in the dorsal horn (DH) of the spinal cord without stimulating the dorsal column fibers responsible for paresthesia. supresses hyperexcitable wide dynamic range neurons (WDR), which are sensitized and hyperactive in chronic pain states.

10kHz stimulation at low amplitude (1-5mA), and short duration/pulse width (30microsec)

vs 30–120 Hz) stimulation at high-amplitude (3.5–8.5 mA), and
longer-duration/pulse-width (100–500 microsec).

HFSCS may also act on the medial pain pathway, which influences attention and pain perception, in addition to the lateral discriminatory pathway.

Question 39

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

Answer 39

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 betwee npatient, 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.

After intraoperative test stimulation, the physician places a temporary extension for a screening test period (up to 10 days). The percutaneous extension wire is taped in place, and sterile dressings are applied. All settings are carefully documented by the clinician.

Question 40

What is the importance of screening test before electrical neuromodulation system implantation

Answer 40

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.
* patient develops understanding of technology + realistic expectations of therapy
* pt is educated and encouraged on trying different parameter settings to optimize and fully test neurostimulation

Question 41

List the guidelines around neurostimulator implantation site

What is the typically recommended site?

Answer 41

• place where skin will not be irritated by restrictive clothing and/or sides of wheelchair
• do not place at belt line
• do not place near pelvic bone or ribcage
• recommended site: abdominal area away from belt line

Question 42

How should the surgeon identify and control for infection

Answer 42

• laboratory testing 1-2 days prior to surgery
• pre and perioperative antibiotics

Question 43

Describe the neurosystem implant procedure

Answer 43

• expose the duramater at the target site of the spinal cord
• introduce lead blank at shallow angle to prepare lead pathway
• remove lead blank andpass surgical lead until the entire lead paddle is in the epidural space
• connect lead to external cable and connect external cable to screener
• disconnect external cable after testing and anchor lead
• create subcutaneous pocket for neurostimulator to be implanted into
• create tunnel for extension wire
• pass extension through tunnel and connect to lead
• connect extension to neurostimulator
• Use the programmer to communicate with the neurostimulator non-invasively,
  establish initial parameter settings and verify system operation.
• Close all incisions. Use the programmer to optimize pain control.

Question 44

Describe the postoperative care after neurostimulation system implantation

Answer 44

• 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 45

What are possible postoperative complications following neurostimulation implant?

Answer 45

• 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 46

What patients are more likely to have post surgical infections?

Answer 46

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

Question 47

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 47

• 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 48

High-Frequency Spinal Cord Stimulation for Pain
* How do they differ from traditional stimulation (3) in surgical procedure
* what is the advantage of high frequency vs low

Answer 48

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

Question 49

When a patient reports dull pain coming from the right shoulder area, but there is no indication of an injury in that area, what alternative origins for this particular pain should be considered, and why?

Answer 49

Referred Pain from Internal Organs
One possibility is that the pain originates from an internal organ and is being referred to the shoulder. Referred pain occurs because sensory information from the skin and internal organs can converge on the same ascending pathway in the spinal cord. The brain, accustomed to receiving pain signals from the skin, interprets the activation of this pathway as pain originating from the skin, even if it stems from an internal organ.
For instance, pain radiating down the left arm could indicate a problem with the heart. Similarly, pain in the right shoulder area could potentially arise from issues with organs like the liver or gallbladder. It’s important to note that this is just a possibility, and further investigation is needed to determine the actual cause of the pain.

Nociceptive Pain from Other Areas
Another possibility is nociceptive pain originating from structures in the neck, upper back, or chest. Nociceptive pain is caused by tissue trauma or mechanical, thermal, or chemical excitation of nociceptors, which are widely distributed in various tissues. This type of pain is often described as dull, aching, or throbbing.
●
Muscle Strain or Spasm: Muscles in the neck, upper back, or chest could be strained or in spasm, referring pain to the shoulder.
●
Joint Dysfunction: Problems with the joints in the cervical spine (neck) or thoracic spine (upper back) could also refer pain to the shoulder.
●
Bone Issues: Conditions like arthritis or bone spurs in the spine can cause pain that radiates to the shoulder.

Neuropathic Pain
While less likely in the absence of a specific injury, neuropathic pain should also be considered. This type of pain results from damage or irritation to nerves in the peripheral or central nervous system. It can be described as burning, tingling, shooting, or electric-like. Potential sources of neuropathic pain that could refer to the shoulder include:
●
Nerve Compression: A nerve in the neck or shoulder could be compressed, leading to pain that radiates down the arm or into the shoulder.
●
Thoracic Outlet Syndrome: This condition involves compression of nerves and blood vessels in the space between the collarbone and first rib, potentially causing shoulder and arm pain.

Question 50

Why might a patient need a partially implanted electrical stimulation system to treat their pain, vs. a simpler to use, totally implanted system.

Answer 50

some potential considerations that might influence the decision between a partially and totally implanted system:
●
Patient Energy Requirements: As mentioned, partially implanted systems are preferred for patients with high energy needs. This suggests that the external power source can provide higher energy output compared to an implanted battery.
●
Battery Life and Replacement: Totally implanted systems rely on an internal battery that will eventually require replacement. This necessitates another surgical procedure. A partially implanted system might be advantageous in cases where frequent battery replacements are anticipated, reducing the need for repeated surgeries.
●
System Complexity and Cost: Totally implanted systems involve a more complex surgical procedure for implantation and might be more expensive overall. Partially implanted systems could be a more practical option in situations where cost or surgical complexity is a concern.
●
Patient Preference and Lifestyle: Some patients might prefer the convenience of a totally implanted system, eliminating the need for an external power source and antenna. Others might find the external components of a partially implanted system acceptable, particularly if it offers benefits in terms of energy output or battery longevity.

Question 51

Why is it that high-frequency (e.g., 10KHz) stimulation systems for pain don’t cause tingling sensations (paresthesia)? It that an advantage or a disadvantage?

Answer 51

Instead of activating the large-diameter Aβ fibers in the dorsal column, HFSCS selectively activates inhibitory interneurons in the dorsal horn (DH) of the spinal cord. Since HFSCS does not stimulate the dorsal column fibers responsible for producing the tingling sensation, patients do not experience it.

Advantages
●
Improved Comfort and Tolerability: Paresthesia can be uncomfortable or even intolerable for some patients
●
Potential for Better Pain Relief: HFSCS has demonstrated superior pain control compared to conventional SCS in some studies
●
Simplified Programming: the programming of conventional SCS relies heavily on patient feedback regarding the location and intensity of paresthesia. With HFSCS, this step is not necessary, potentially simplifying the programming process.

one potential consideration is the loss of a feedback mechanism for clinicians.
●
Confirmation of Stimulation: In conventional systems, the presence of paresthesia provides immediate confirmation that the stimulation is reaching the intended target. Without this sensory feedback, clinicians might need to rely more heavily on indirect measures to confirm the effectiveness of stimulation.