Central neuropathic pain
e.g. Spinal cord injury, stroke, MS, syringomyelia
Peripheral neuropathic pain
e.g. Postherpetic neuralgia, radiculopathy, phantom limb pain, polyneuropathy
Mixed neuropathic pain
e.g. Post herpetic neuralgia
Occurs in 20% of diabetics
20-50% of herpes zoster patients develop PHN
Post-surgical >10%
1/3rd of cancer patients
>50% of low back pain may have some associated neuropathic pain
Screening tools:
DN4
LANSS
Neuropathic pain scale questionaire
Pain DETECT
When working out neuropathic pain - you NEED to make sure it is neuroanatomically plausible
Mechanisms:
Lowered threshold of firing
Increased Na channel density
Chemical excitation of non-nociceptors
Recruitment of nerves just outside the injured area (Ephaptic)
Ectopic discharge
Loss of inhibitory pathways
Central sensitisation (maintained by peripheral stimulation)
Antidromic neurogenic inflammation
Problems treating neuropathic pain:
Higher average pain scores
Lower QOL
Higher pharmacological load
Less pain relief with treatment
Inability to tolerate treatments is common
Prevention of neuropathic pain:
Amitriptyline has been shown to reduce prevalence and severity of post-herpetic neuralgia by 50% compared to placebo
Use of antivirals has been shown to reduce the severity and duration of pain in PHN
Operative techniques for PSP and amputation pain are important. Ketamine has mixed evidence for prevention - better for Post surgical prevention now.
References / Articles / Resources
FPM Module 4
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