Neurostimulation for Pain

Question 1

Spinal Cord Stimulation (Type, Complexity and burden, MOA)

Answer 1

Type:

• Implantation of electrodes in the epidural space which deliver a current to the underlying posterior columns
• Typically undergo after a trial using percutaneous leads to determine if stimulation to the affected area can lead to meaningful analgesia

Complexity/Burden:

• Invasive - implantation of the entire system
• Outpatient surgical procedure
• Middling level of burden to patient

Mechanism

• Modulation of pain signals at the level of the spinal cord
• Notion that stimulation of large-diameter afferents in the psterior columns could segmentally inhibit transmission from impulses originate in small diameter nociceptive afferents
• May also inhibit transmission in the spinothalamic tract by activatin central descending inhibitory mechanisms

Risks:

Evidence:

• Most literature reports on patients with neuropathic pain (e.g. radiculopathies, chronic regional pain syndrome, phantom limb pain)
• Few reports of it used for visceral pain
• No good RCTs in patients with advanced illness

Question 2

Transcutaneous electrical stimulation (Type, Complexity and burden, MOA)

Answer 2

Type:

• Electrodes placed on the skin along the distribution of the peripheral nerve innervating the painful region
• Stimulation to the underlying area

Complexity/burden

• Non-invasive
• Minimal burden

Mechanism:

• Based on ‘gate theory’ - vibration can inhibit pressure/pain thresholds mediated by second-order neurons in the dorsal horn of the spinal cord
• May also result in met-encephalin or dynorphin release that activates delate opioid receptors at supraspinal and spinal levels

Evidence:

• Limited evidence to support
• Anecdotal experience suggests benefits in mixed neuropathic and nociceptive syndromes

Risks:

• Concerns about TENS resulting in increased blood flow at the site as it could increase angiogenesis or tumour spread (theoretical)
• Patient response is highly variable
• Skin irritation and mild discomfort may occur
• Avoid with pacemakers, and avoid use near carotid sinus, epiglottis, and abdomen/low back of pregnant women

Question 3

Peripheral Nerve Stimulation (Type, Complexity and burden, MOA)

Answer 3

Type:
- Percutaneous implantation of electrodes in the subcutaneous tissue adjacent to the peripheral nerve that innervates the affected area

Complexity/burden

• Invasive
• Outpatient surgical procedure
• Middling level of burden to patients

Mechanism:

• Impulse interruption by collision
• Gate control within the spinal cord or supra spinal locations
• Inhibition of neuroma spontaneous activity

Evidence:
- No RCTs or research in advanced illness

Risks:

• Risk of nerve injury minimal
• No nerve dissection required

Question 4

Transcranial direct current stimulation (tDCS) (Type, Complexity and burden, MOA)

Answer 4

Type:

• Placement of electrodes on the scalp and forehead with low intensity direct current
• Creates an electrical field between the two electrodes and modulates the firing rate of individual neurons - may be anodal (excitatory) or cathodal (inhibitory)

Complexity/burden

• Non-invasive
• Minimal burden to patient

Mechanism

• Subthreshold modulation of neuronal resting membrane potential
• Results in changes of NMDA receptor

Risks:
- Only if high levels of current used (tissue damage)

Evidence:

• Support for it in a variety of chronic pain syndromes and may also improve sleep, quality of life, and use in pain medications
• A few RCTs
• Duration of effect varies widely

Question 5

Transcranial magnetic stimulation (Type, Complexity and burden, MOA)

Answer 5

Type:
- Generation of a magnetic field placed on the scalp to stimulate the underlying brain tissue

Complexity/burden

• Non-invasive
• Delivery can be painful
• Low burden to patient
• May be delivered once or as a series

Mechanism:

• Modulation of brain neuronal excitability under the magnetic field, as well as connections to other parts of the brain
• More selective regional neuromodulation than transcranial direct current stimulation

Risks:

• Minimal
• Headaches, tingling, lightheadness, etc.

Evidence:

• Higher frequencies appear to be more effective in eliciting long lasting pain relief
• No studies in populations with acute or chronic pain related to serious illnesses, but evidence to support in neuropathic pain and acute headache

Question 6

Deep brain stimulation (Type, Complexity and burden, MOA)

Answer 6

Type:
- Leads placed in deep brain structures

Complexity/burden

• Invasive
• Inpatient surgical intervention
• High level of burden to patients

Mechanism

• Modulates the activities of certain brain areas (e.g. hypothalamus, thalamus, periaquaductal gray)
• Exact mechanism unknown

Risks:

• Very invasive - infections, ICH, paralysis, etc.
• Stimulation side effects (paresthesias, dysarthria, gait disturbances, mood or personality changes, etc.)
• Patient selection should include a mental health professional.

Evidence:
- May be effective in cluster headache, chronic pain

Question 7

Motor cortex stimulation (Type, Complexity and burden, MOA)

Answer 7

Type
- Grid of electrodes surgically placed on motor cortex

Complexity and burden

• Invasive
• Inpatient procedure, requires fMRI for placement
• High level of burden

Mechanism
- Modulates the activity of the underlying cortex and connections to other brain areas

Risks:
- Invasive

Evidence

• Less than for deep brain stimulation
• Favourable case reports for chronic neuropathic pain, but no published trials in advanced illness