Treatment of Neuropathic Pain Flashcards
What is the opposite of neuropathic pain and what does it respond well to?
Nociceptive pain - usually the result of damage to normal tissue
responds well to opioids and NSAIDs
What is neuropathic pain? How does this relate to what it best responds to?
Pain initiated or caused by a primary lesion or dysfunction in the nervous system -> not a tissue damage
This is the reason why it responds best to anticonvulsants / antidepressants -> neuromodulators
What is central vs peripheral neuropathic pain and which are the most well studied?
Distinction made between where the lesion occurs, though a given syndrome may have components of both.
Peripheral - all the most well studied neuropathic pain, including:
- Post-herpetic neuralgia
- Diabetic neuropathy
- Trigeminal neuralgia
What is the role of the cortex to suppress pain and how can neurotransmitter imbalance affect this?
Cortex sends down descending pathways which release NE, 5-HT, and GABA to facilitate the inhibition of excitatory pain impulses
-> pain loop should shut off overtime
How does peripheral sensitization occur?
- Inflammation damages or destroys peripheral nerves
- Threshold for firing is lowered, as regeneration of nerve triggers development of excess Na+ and adrenergic channels.
- Peripheral neurons fire impulses spontaneously leading to pain
What is the definition of chronic pain?
Pain which persists after healing for >3 months
What channels are modified to cause central sensitization?
In the descending axon which is normally inhibitory:
- Enhanced NMDA release on pain receptors and hence calcium influx
- Reduced GABA activity
- Reduced norepinephrine
What drugs block calcium channels in treatment of neuropathic pain?
- Gabapentin
- Pregabalin
- Topiramate
What drugs block sodium channels in the treatment of neuropathic pain?
Carbamazepine
Lidocaine
TCA’s
How else are TCAs effective in the treatment of neuropathic pain than just sodium channel blockade?
Increase NE and 5HT in the synapse by inhibiting their reuptake
What is the mechanism of capsaicin in treating neuropathic pain?
It is thought to deplete substance P acutely so that it cannot be used to chronic cause increased pain signals
-> questioned efficicacy
What type of pain is neuropathic pain usually described as? What other symptoms often go with it?
Shooting or stabbing pain, or “Shock-like” electric pain.
Orthostatic hypotension - autonomic neuropathy
Bowel dysmotility - autonomic neuropathy
Stocking and glove pattern -> distal sensory polyneuropathy
Is neuropathy common in diabetes and why?
Yes - up to half of all patients experience it, and 20% have neuropathic pain
-> accumulation of sorbitol in peripheral nerves leads to oxidative stress
What drug classes are most closely associated with neuropathic pain?
Anti-retrovirals & HIV itself
Cancer chemotherapy** - cisplatin, vincristine, paclitaxel, thalidomide
Antibiotics - isoniazid
If you have shingles, what early intervention should be given to prevent severe post-herpetic neuralgia?
Early antivirals as well as steroids to control the immune response
