FRCA Notes

Neuropathic Pain

Resources

  • Neuropathic pain arises as a direct consequence of lesions or disease affecting the somatosensory system
  • There is no requirement for for the pain to be chronic, although it is often assumed to be so

Central neuropathic pain

  • Describes pain arising from a lesion/disease anywhere in the spinothalamo-cortical pathways
  • Mechanism of development is not well understood, although it involves disinhibition, sensitisation and maladaptive neuroplastic changes
  • Examples include:

Peripheral neuropathic pain


  • Clinical features may be positive or negative or both

Positive symptoms (i.e. abnormally increased sensations)


Symptom Definition
Hyperaesthesia Increased sensitivity to a stimulation
Hyperalgesia Increased response to a normally painful stimulation
Dysaesthesia Unpleasant sensation resulting from a stimulus which would not normally be unpleasant
Allodynia Painful response to a stimulus which would not normally be painful
Paraesthesia Abnormal sensation which is neither unpleasant nor painful: often tingling, prickling or heat sensation
Hyperpathia Abnormal response to a normally painful stimulation
e.g. altered location, identification, radiation and after-sensation may be present

Negative symptoms (i.e. abnormally reduced sensations)


Symptom Definition
Hypoaesthesia Decreased sensitivity to stimulation
Hypoalgesia Decreases sensitivity to normally painful stimulation
Hyperpathia May be a positive or negative symptom

Physical signs


Sign Examples
Trophic change Hair changes, skin thickening
Vasomotor Temperature, colour change and oedema
Sudomotor Sweating changes
Musculoskeletal Muscle wasting, osteopaenia


  • Standard pain assessment tools are not necessarily valid in neuropathic pain conditions
  • Specialised scales for neuropathic pain are used instead, which have a sensitivity and specificity as high as 90%
  • Also benefit from being able to be administered by non-specialists and patients themselves
  • However:
    • Fail to identify up to 20% of neuropathic pains depending on the context
    • Limited clinical examination involved
    • Do not provide information about the neurological lesion
    • Difficult to apply for multiple pain areas

Pain assessment tools for neuropathic pain

  • PainDETECT
  • Neuropathic Pain Score
  • LANSS; Leeds Assessment of Neuropathic Symptoms and Signs
  • Doleur Neuropathique en 4 (DN4)

  • Identification and treatment of underlying cause

Non-pharmacological

  • MDT: physiotherapy, occupational therapy
  • Psychological: CBT, hypnotherapy
  • Liaison with GP, IP and OP pain services

Pharmacological

  • First line
    • ɑ2δ ligands e.g. gabapentin, pregabalin, mirogabalin
    • Anti-epileptics e.g. carbamazepine, oxcarbazepine, lacosamide, and lamotrigine
    • SNRIs e.g. duloxetine, venlafaxine
    • TCAs e.g. amitriptylline, nortriptylline

  • Second line
    • Lidocaine 5% plasters
    • Capsaicin 8% cream - binds TRPV1 receptors causing retraction of intra-epidermal axonal endings i.e. 'defunctionalisation'

  • Others inc. experimental
    • Baclofen (GABAB agonist)
    • Ketamine (NMDA antagonist)
    • Tramadol (mixed mu opioid receptor and monoamine reuptake effects)
    • Botulinum toxin type A injections

Interventional

  • Neurostimulation

  • Surgical intervention e.g. in trigeminal neuralgia, lumbar radiculopathy