Neuropathic Pain

Question 1

Define neuropathic pain

Answer 1

Neuropathic pain is pain caused by a lesionor disease of the somatosensory nervous system.

Question 2

Peripheral neuropathic pain vs. central neuropathic pain with examples

Answer 2

Peripheral NP - Pain caused by primary lesion or disease in peripheral somatosensory system.

E.g. Chemotherapy, diabetic

Central NP - Pain caused by primary lesion or disease in central SS system.

E.g. Spinal cord injury, post-stroke pain

Question 3

Describe the type of stimuli, response and purpose of the pain response for nociceptive pain.

Answer 3

• Noxious stimuli (e.g. heat, cold, chemical irritants)
• Act through nociceptive sensory neuron to signal pain
• Adaptive - high threshold - acts as early warning system

Question 4

Describe the stimuli, response and purpose of inflammatory pain

Answer 4

• Inflammatory mediators (macrophages, neutrophils, TNF-alpha etc)
• Create pain hypersensitivity
• Adaptive, low-threshold, tenderness promotes repair

Question 5

Describe the stimuli, response and purpose of neuropathic pain.

Answer 5

• Neural lesions, peripheral nerve damage
• Create hyperalgesia and spontaneous pain
• Maladaptive, low-threshold pain.

Question 6

How does nerve damage cause peripheral sensitisation?

Answer 6

Damaged nerve regrows and expresses receptors for inflammatory mediators (bradykinin)

• Lowers threshold for peripheral nociceptor activation
• Increase in receptive field of pain fibres
• More sodium and voltage dependent calcium channels

Results in exaggerated pain from stimuli which would not normally cause pain.

Question 7

Difference between hyperalgesia and allodynia.

Answer 7

Hyperalgesia is you are sensitised to pain stimuli, causing an exaggerated response.

Allodynia is a painful response to non-noxious stimuli, due to both peripheral and central sensitisation.

Question 8

How does peripheral sensitisation cause central sensitisation

Answer 8

Continued input from peripheral sensitisation results in central sensitisation at the spinal cord.

Question 9

List positive and negative sensory signs and symptoms for neuropathic pain.

Answer 9

Positive:

• Dysesthesias (burning, itching etc)
• Paraesthesias (pins and needles)
• Spontaneous pain

Negative:

• Loss/impairment of sensory quality
• Numberness and reduced sensation

Question 10

Three concepts for treatment of neuropathic pain

Answer 10

1. Dampen down peripheral sensitisation in the damaged axon (Na+ channel blockade)
2. Dampen down central sensitisation (NMDA antagonists and calcium channel blockers)
3. Enhancing descending inhibitory pathways (Tricyclics/SNRIs)

Question 11

Mechanism behind dorsal horn (central) sensitisation)

Answer 11

NMDA receptrs in post-synaptic membrane in dorsal horn.

Continued signals from PNS allows too much calcium in teh cell - hyper-excitable state

Question 12

Treatment for neuropathic pain: First line, second line and third line.

Answer 12

First line:

• Gabapentin
• Tricyclic antidepressants
• Serotonin-noradrenaline reuptake inhibitors

Second line:

• Tramadol

Third line:

• Strong opioids