neuropathic pain

see also:

• pain, analgesia and analgesics
• sensory & motor testing including dermatomes, myotomes, reflexes, coordination & balance
• Addiction medicine - drug and alcohol
• Pain Management Research Unit, Sydney

• diabetic neuropathy - pain in feet/ankles in up to 15% of diabetics
• post-herpetic neuralgia - 7-27% with past herpes zoster & incidence increases with age
• uncommonly referred neuropathic leg pains may occur in patients with genital Herpes simplex virus (HSV)
• trigeminal neuralgia - sudden, brief, very severe paroxysms of pain - 5-8 per 100,000 people per year, females 2x males.

• managing neuropathic pain is challenging - only half of those treated gain partial pain relief
• treat early to prevent transition to persistent pain
• once established, it is difficult to treat particularly when neuronal damage is irreversible.
• unless there is nociceptor stimulation, most neuropathic pain is refractory to simple analgesics although a short course can be tried and thus the role for opiates and opioids is limited.
• non-drug strategies may be of benefit
  • eg. TENS - see electrotherapy modalities - TENS
• there is limited evidence for the efficacy of these drugs hence no generally accepted step-wise approach.
• start with one drug at a time & allow a trial period to assess response
  • for diabetic or zoster pain, usually start with an antidepressant or an anticonvulsant such as gabapentin.
    • tricyclic antidepressants appear to relieve pain independent of their antidepressant action, and at smaller doses:
      • amitryptiline (Endep)or nortryptiline:
        • start at 10mg at night and increase by 10mg every 7 nights to a maximum dose of 150mg nocte.
    • gabapentin (Neurontin)
      • start with 100mg tds, increase to 300mg tds over 7 days, increase by 100-300mg every 5 days to max. 3600mg daily.
    • other options for diabetic neuropathy pain:
      • topical capsaicin 0.075%
      • carbamazepine 200mg bd to qid
      • opiates and opioids eg. oxycodone 10-100mg daily, tramadol 100-400mg daily
      • pregabalin (Lyrica) 150-600mg daily
      • serotonin-NA reuptake inhibitors:
        • venlafaxine 150-225mg daily
        • duloxetine 60-120mg daily
    • other options for herpetic pain:
      • pregabalin (Lyrica) 75mg bd, if needed, increase to 150mg bd after 7 days then to maximum dose of 300mg bd after further 7 days.
      • topical capsaicin 0.075%
      • topical lignocaine
      • limited evidence for opiates and opioids:
        • tramadol 50mg daily increase by 50mg evry 3-4 days to to 100mg qid
  • trigeminal neuralgia
    • carbamazepine:
      • 50-100mg once or twice daily, gradually increase up to 400-800mg in 2-4 divided doses (max. 1600mg per day)
      • after 1 month pain free, gradually taper then stop
      • if not tolerated, or ineffective, consider:
        • oxcarbazepine (an analogue of carbamazepine)
          • seems to be effective for up to 3-4 years in up to two thirds of those who cannot tolerate carbamazepine or its efficacy has declined.
          • 150mg bd, increase to 300mg evry 3 days if needed to usual dose 300-600mg bd (max. dose 900mg bd)
          • no PBS approval other than for Rx epilepsy!
        • other anticonvulsants
          • gabapentin (Neurontin)
          • lamotrigine
          • phenytoin
        • referral to neurosurgery