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NEUROPATHIC PAIN
Neuropathic pain is the sensation of pain due to abnormal discharges of impaired or injured neural structures in the peripheral &/or central nervous system.
It is characterized by hyperesthesia, hyperalgesia and allodynia.
Common neuropathic pain syndromes are central neuropathic pain, painful diabetic peripheral neuropathy, postherpetic neuralgia, trigeminal neuralgia, postsurgical neuropathic pain, HIV-related neuropathy, lumbosacral radiculopathy and complex regional pain syndrome.

Surgical Intervention

Trigeminal Neuralgia (TN)

  • For patients with TN refractory to medical therapy, early surgical therapy may be considered
  • Prior to considering surgery, eligible patients should have an MRI to eliminate other causes of compression of the trigeminal nerve
  • Peripheral Techniques
    • Involve blocking or destruction of portions of the trigeminal nerve distal to the Gasserian ganglion
    • Low morbidity but 50% have pain recurrence after 1 year
  • Percutaneous Procedures on Gasserian Ganglion
    • Preferred for elderly patients, those with multiple sclerosis (MS), with impaired contralateral hearing, and those with recurrent pain after microvascular decompression
    • Eg radiofrequency thermocoagulation, balloon compression rhizotomy, percutaneous retro-Gasserian glycerol rhizotomy
      • A median of 68% (range 55%-80%) of patients who underwent balloon compression remain pain-free after long-term follow-up
    • After percutaneous trigeminal radiofrequency, initial pain relief can be achieved in 98% of patients & 15-20% of patients may experience recurrence in 12 months
      • Pain-free period is reported at 4-5 years
    • Observational studies have shown that radiofrequency thermocoagulation produces higher rates of complete pain relief but is also associated with higher rates of facial numbness and corneal insensitivity
      • A median of 58% (range 26%-82%) of patients remain pain-free after long-term follow-up 
      • Severe facial numbness/anesthesia dolorosa and corneal numbness with keratitis occur in around 4% of patients
  • Microvascular Decompression
    • Preferred procedure for young patients with typical TN
    • Major neurosurgical procedure involving craniotomy to reach the trigeminal nerve in the posterior fossa
    • Vessels compressing the nerve are identified and moved out of contact
    • Provides longest duration of pain relief while preserving facial sensation
      • Observational studies have shown a median of 77% (range 62%-89%) of patients remain pain-free at long-term follow-up (10-12 years)
    • Complications include aseptic meningitis, hearing loss, cerebrospinal fluid (CSF) leaks, infarcts, hematomas, transient diplopia and sensory loss
    • Associated with 0.5% mortality rate and 3-29% facial numbness rates
    • Increased risk for severe complications in older age groups
  • Gamma Knife Stereotactic Radiosurgery
    • Least invasive procedure for TN
    • Treatment option for patients with comorbidities, high-risk medical illness or pain refractory to prior surgical procedures
    • Aims a focused beam of radiation at the trigeminal root in the posterior fossa
    • In a study, it showed that adequate pain relief were 75%, 60% & 58% at 1, 3, & 5 years, respectively
      • Pain-free period is reported at 3-4 years 
      • Onset of pain relief is variable with an average time of 1 month or median time of 2 weeks after treatment
    • Most common adverse effect is trigeminal nerve sensory dysfunction eg facial numbness, paresthesia
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