Neuropathic Pain Flashcards
What are the positive symptoms of sensory nerve neuropathy?
- paraesthesia (abnormal sensations that can become intense and/or painful)
- dysesthesia (altered sensations including numbness, tingling, or “pins and needles” sensations, that are usually painless and temporary)
- hyperalgesia (abnormal increased sensitivity to pain)
- allogdynia (pain from a stimulus that does not normally cause pain)
What are the negative symptoms of sensory nerve neuropathy?
- numbness
- hypoalgesia (decreased sensitivity to painful stimuli)
- hypoesthesia (loss of sensation to heat, pain, touch e.g. numbness)
What are the positive symptoms of motor nerve neuropathy?
- fasciculations (spasticity/repeated involuntary movements)
- hypertonicity (increased muscle tone)
What are the negative symptoms of motor nerve neuropathy?
- hypotonicity (low tone)
- flaccidity (relaxed muscle)
- paralysis (inability to move)
What characteristics are used to describe nerve pain?
- pricking/lancinating
- sharp/lacerating
- pinching/crushing
- tugging/wrenching
- hot/searing
- tingling/stinging
- shooting is sometimes used to describe nociceptive pain, however, depends on direction of travel e.g. jabbing into back or down the leg
What is meant by a ‘positive’ or ‘negative’ symptom/sign of nerve compromise?
- positive = increasing = up regulation of sensation e.g. hyperalgesia, clonus, tingling, fasciculation
- negative = removing = down regulation of sensation e.g. numbness, analgesia, dysathesia, Parathesia, weakness
Describe the macro structure of a nerve
- nerves are large structures
- require good blood supply and lymphatic drainage
- require good nociception to detect mechanical and inflammatory injury
What are the nerve-to-nerve supply called?
- nervi-nervorum
What is the blood supply to a nerve called?
- vaso-nervorum
What are the most compressive structures in the body?
- lymph > veins > arteries > nerves
What changes happen following nerve damage?
- injury to nerve e.g. crush injury (peripheral)
- nerve dies back
- existing nerves increase sensitivity (cytokines) => mechanical, thermal + chemical stimulus => increasing nociception in dermotome => peripheral + central axon growth
- also get ectopic action potentials (in an abnormal place) going back to the nerve root up to the brain from sympathetic nerves, which wouldn’t usually enter the nervous system (nerve growth factor of sprouting)
- sympathetic receptors get deposited in epidermis, resulting in shooting pain from a painful event
- results in numbness + hyperalgesia
What happens during central sensitisation without neuropathic pain?
- prolonged activity in dorsal horn synapse => Astrocytes activated
- Astrocytes release CCL2 => upregulating NMDA receptor
- reuptake of glutamate is inhibited (more excitatory stimulus goes to dorsal horn)
- GABA reuptake is increased (more inhibitatory stimulus taken back into system => less inhibition)
- enhances sensitisation of the synapse
What happens in central sensitisation during neuropathic pain?
- nerve injury => microglia activated by cytokines (CX3CL1)
- Microglia upregulated => releases more cytokines into synapse and astrocytes
- reuptake of glutamate is inhibited (more excitatory stimulus goes to dorsal horn)
- GABA reuptake is increased (more inhibitatory stimulus taken back into system => less inhibition)
- enhanced allodynia + hyperalgesia as well as spontaneous pain (due to spontaneous firing of injured neuron)
Signs and symptoms of neuropathic pain
- history of nerve injury, pathology or mechanical compromise
- pain referred in dermotomal or cutaneous distribution
- pain/symptom provoked with mechanical movement e.g. move, load, compression of neural tissue
- directional pain (down leg)
- pain significantly higher with reduce quality of life
- requires strong meds
- prolonged prognosis
- more likely to become chronic => requires quick diagnosis and management plan for life
What is the differences between neuropathic pain and nociceptive pain?
- Nociceptive:
—> involves activation of nerve endings in tissue
—> local to the injury tissue (but can refer)
—> absence of tingling, numbness etc.
—> sensitive to heat (heat hyperalgesia)
Neuropathic:
—> involve nerve damage
—> referred to distal nerve territory (peripheral/dermal neural map)
—> associated with tingling, numbness
—> sensitive to cold (cold hyperalgesia)
—> stress can directly activate nociceptor
