Neuropathic Pain Flashcards
What is neuropathic pain?
- pain initiated by lesion or dysfunction of the somatosensory system, resulting in abnormal activity of the somatosensory pathway
- can result from drugs, disease or trauma
What is nociceptive pain?
acute pain associated with injury and inflammation
What are some triggers of neuropathic pain?
- alcoholism
- amputation
- diabetes
- drugs (ex. chemo)
- herpes zoster (shingles)
- HIV or AIDS
- MS
- spinal injury
- stroke
- tumor
What are the name of the nerve fibers that carry pain and temperature sensations?
A gamma - small, myelinated
C - small, demyelinated
What is the name of the nerve fiber that carries touch sensations?
A beta fibers - large, myelinated
- these are the fibers that contribute to allodynia
What is allodynia?
Pain resulting from a non-painful stimulus
Where is myelin produced in the PNS?
CNS?
Schwann Cells
Oligodendrocytes
Describe the pain pathway from the source
- pain source in A gamma and C nerve fibers
- peripheral nerves to afferent dorsal horn
- into brain’s sensory cortex
Excitatory neurotransmitters bind to post-synaptic membranes and cause _______________.
What are the excitatory neurotransmitters?
depolarization
Glutamate (A gamma)
Substance P (C)
Aspartate
Inhibitory neurotransmitters bind to post-synaptic membranes and cause _______________.
What are the inhibitory neurotransmitters?
hyperpolarization
GABA
Glycine
What can cause hyperexcitability?
- increase of excitatory NTs
- decrease of inhibitory NTs
- increase of cell permeability (Na+ and Ca2+ will increase intracellularly)
What does the term “windup” mean when referring to NPP?
- when adjacent neurons produce AP due to ectopic firing
- increases the pain signal
What happens to the pain signal when the inner cell becomes more positive?
The pain signal will become stronger
What are the symptoms of NPP?
- burning
- tingling
- pins and needles
- shooting
- stabbing
- numbness
- jabbing
- throbbing
- aching
What is hyperalgesia?
higher pain response than usual to a normally painful stimulus
What is paraesthesia?
abnormal numbing or prickling of skin
What is the pain triad of NPP?
- NPP
- Psychological symptoms
- Sleep Disturbances
can include:
- insomnia
- fatigue
- lack of concentration
- depression
- anxiety
- stress
How to TCAs (tricyclic antidepressants) help with NPP?
- they block the tricyclic reuptake of NE and 5-HT
- blocks Na+ and Ca2+ channels
- blocks NMDA receptors
- that will help with mood
- serotonin is good for sleep
- so TCAs will help with mood, pain and sleep
How is NPP diagnosed?
- DN4 questionnaire (4 or more/10 = NPP)
- visual analogous scale
- clinical presentation of 2-3 sx
What are the 4 point of focus to treat NPP?
- inhibition of first order sensory afferents (site of pain)
- synaptic inhibition between 1st order sensory afferent and DRG
- synaptic inhibition between DRG and dorsal horn interneurons
- synaptic inhibition between dorsal horn interneurons and ascending tract
APs can be regulated by decreasing excitation or increasing inhibition.
How do we do this?
Decreasing excitation:
- Na+ blockers
- inhibit Ca2+ channels
- block excitatory NTs (Glutamate, Aspartate, Substance P)
Increase inhibition:
- GABA agonists
- NE and 5-HT reuptake inhibitors
How do antiepileptics help with NPP?
- reduce influx of Na+ and Ca2+
- enhance inhibitory effects of GABA
- reduce concentration of glutamate and/or blocks NMDA receptors
How do SSRIs help with NPP?
- it inhibits serotonin reuptake without affecting NE
Can NPP be cured?
- only 20% of patients have complete pain cessation with treatment
- the other 80% can only have their pain lowered to a more tolerable level.
