Neuropathic Pain

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Neuropathic Pain

• Dr Jacqueline Yap

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Epidemiology

• HK telephone survey
• Prevalence of chronic pain 10.8
• Ng JKF et al CJP 2002
• NTE outpatient pain clinics survey
• n248 over 4mth
• Median duration of pain 2.3 y
• 28 had tried 5 or more treatment

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Type of pain

• Back pain 44.4
• Neuropathic 27
• Joint pain 8.9
• Other muscle pain 7.7
• Unknown 3.6

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What is neuropathic pain?
Nociceptive Pain
Neuropathic Pain

• Pain caused by a painful stimulus

• Pain initiated or caused by a primary lesion or
  dysfunction in the nervous system

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Features of neuropathic pain (1)

• Continuous burning pain
• Intermittent lancinating or shooting pain
• Electric shock-like pain
• Nearly always has sensory deficit or distortion

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FEATURES OF NEUROPATHIC PAIN
COMPONENT DESCRIPTORS EXAMPLES
Steady, Dysaesthetic Burning, Tingling Constant, Aching Squeezing, Itching Diabetic neuropathy Postherpetic neuralgia
Paroxysmal, Neuralgic Stabbing Shocklike, electric Shooting Lancinating Trigeminal neuralgia may be a component of any neuropathic pain
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Features of neuropathic pain (2)

• Paresthesias abnormal spontaneous,
  intermittent, painless
• Dysesthesia abnormal spontaneous or
  touch-evoked, unpleasant

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Neuropathic Pain Evoked Dysesthesias

• Allodynia pain elicited by a non-noxious
  stimulus (clothing, air movement, touch)
• Mechanical (induced by light pressure)
• Thermal (induced by a nonpainful or warm
  stimulus)
• Hyperalgesia exaggerated pain response to a
  mildly noxious (mechanical or thermal) stimulus
• Hyperpathia delayed and explosive pain response
  to a noxious stimulus

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State of normosensitivity
Low intensity stimulation
High intensity (noxious) stimulation
Innocuous sensation
PAIN
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State of hypersensitivity spontaneous pain
Low intensity stimulation
High intensity (noxious) stimulation
Innocuous sensation
PAIN
INCREASED PAIN
(Allodynia)
(Hyperalgesia)
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Mechanisms

• Peripheral
• Peripheral sensitization
• Ectopic discharges
• Central sensitization
• Ectopic discharges
• Reorganization of Ab fibres
• Loss of inhibitory control

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Physiology of nociception
Noxious stimulus
Response
DRG
Pain neuron
Soup of inflammatory agents (histamine,
serotonin, prostaglandins, bradykinin)
PNS
CNS
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Peripheral Sensitization
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Ectopic Impulses
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Central Sensitization
Glutamate
PresynapticMembrane
SubstanceP
Ca2
PostsynapticMembrane
NK-1
AMPAReceptor
NMDAReceptor(Depolarized)
Ca2
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Reorganization of Ab fibers
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Stimulus Dependent Central Sensitization
1. A beta activation will not stimulate
pain-mediating DH neurones
Abeta mechanoreceptor
NORMAL
non-painful
innocuous stimulus
NERVE INJURY
Abeta mechanoreceptor
innocuous stimulus
painful
2. Increased nociceptor drive leads to central
sensitisation
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Loss of Inhibitory Controls
Descending
Local
To brain
NORMAL
Dorsal horn neuron
Descending
Local
To brain
INJURED
Exaggeratepain response
Innocuous ornoxious stimulus
Woolf, 1999.
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Central sensitization

• Increase sensitivity excitability
• Reduce nociceptive threshold
• Increase receptive field size
• Increase in magnitude and duration of response to
  stimuli
• Long term responses

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Neuropathic pain

• Diverse syndromes with uncertain classification
• Mononeuropathies and polyneuropathies
• CRPS
• Deafferentation syndromes, including central pain

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Some neuropathic pain syndromes

• Central
• Brain stem, thalamic, cortical, subcortical
  lesions eg post-stroke, MS, tumour
• Peripheral
• Postherpetic neuralgia
• Radiculopathy eg PID
• Phantom limb pain
• Diabetic neuropathy
• Chronic regional pain syndrome (CRPS)

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Chronic pain postop

• Phantom pain 30-80
• Thoracotomy gt50
• Breast surgery
• Scar 11-57
• Phantom 13-24
• Cholecystectomy 3-56
• Hernia repair 0-27

Perkins, Kellett. Anaesthesiology
2000931123-2236
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Neuropathic Pain Clinical Assessment

• A comprehensive diagnostic approach to patients
  affected by neuropathic pain
• Medical history
• Examinations
• general, neurologic, regional
• Diagnostic workup
• imaging studies, laboratory tests, nerve/skin
  biopsies, electromyography/nerve-conduction
  velocity (EMG-NCV) studies, diagnostic nerve
  blocks

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Medical History

• Ask patient about complaints suggestive of
• Neurologic deficits persistent numbness in a
  body area or limb weakness
• Neurologic sensory dysfunction touch-evoked
  pain, intermittent abnormal sensations,
  spontaneous burning and shooting pains

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Neurologic and Regional Examinations

• In patients with neuropathic pain, examination
  should focus on the anatomic pattern and
  localization of the abnormal sensory symptoms and
  neurologic deficits

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Diagnosis

• Radiological Investigations
• EMG-NCV and QST
• To localise pain-generator/nerve or root lesion
• To rule out
• Axonal vs focal segmental demyelination
• Underlying small-fiber or mixed polyneuropathy
• Nerve skin biopsy
• quantify epidermal innervation density

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Neuropathic pain Management

• Pharmacotherapy
• Nonopiod
• Adjuvant analgesics
• (Opioid)
• Interventional
• Neural blockade (eg. Sympathetic nerve blocks)
• Neurostimulatory techniques (eg. Spinal cord
  stimulation)
• Intraspinal infusion

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35 yo lady amputation of right arm for cancer.
Postop given iv PCA morphine for pain control.
APS team review from D1-D3 postop noted
increasing high usage of morphine PCA (up to
100mg/day). However, patient still reported
unsatisfactory pain control with PCA. Patient
seemed very distressed.
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Phantom pain. Started on amitriptyline. Gabapenti
n added later. Pain improved.
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Neuropathic pain Pharmacologic Therapies

• Anticonvulsants (gabapentin)
• Antidepressants (amitriptyline)
• Opioid analgesics (methadone)
• Local anaesthetics (lignocaine)
• Alpha-2 adrenergic agonists (clonidine)
• NMDA receptor antagonists (ketamine)
• NSAIDS

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Interventional procedures
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Spinal cord stimulator
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External factors
Loeser Cousins 1990
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PHYSICAL
SUFFERING
PSYCHOSOCIAL
EMOTIONAL
SPIRITUAL
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Neuropathic Pain Management

• Rehabilitative approaches
• physiotherapy
• Psychologic intervention
• cognitive behavioural therapy (CBT)

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Neuropathic pain Management

• Pharmacotherapy
• Interventional
• Physiotherapy
• Psychological
• MULTIDISCIPLINARY
• BIOPSYCHOSOCIAL

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80 yo man complains of severe burning pain over
the area of shingles he had 2 months ago.
Associated allodynia, insomnia, depression.

• Initial treatment with Gabapentin topical
  lignocaine
• Treat depression
• Epidural steroid

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45 yo complains of paroxysmal electric shock-like
pain over left mandible that last for a few
seconds. Pain free in between attacks.
Frequency 3-4 times/day. Some sensory impairment
over mandible.

• Initial treatment carbamazepine
• Further consultation Ix
• Surgery

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Conclusions

• More effective medical therapies for neuropathic
  pain are becoming available, and should be used
  to limit unneccesary suffering, with the ultimate
  goal of improving patients quality of life