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Neuropathic Pain

Neuropathic Pain. Dr Jacqueline Yap. Epidemiology. HK telephone survey Prevalence of chronic pain 10.8% Ng JKF et al CJP 2002 NTE outpatient pain clinics survey n=248 over 4mth Median duration of pain = 2.3 y 28% had tried 5 or more treatment. Type of pain. Back pain 44.4%

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Neuropathic Pain

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  1. Neuropathic Pain Dr Jacqueline Yap

  2. Epidemiology • HK telephone survey • Prevalence of chronic pain 10.8% Ng JKF et al CJP 2002 • NTE outpatient pain clinics survey • n=248 over 4mth • Median duration of pain = 2.3 y • 28% had tried 5 or more treatment

  3. Type of pain • Back pain 44.4% • Neuropathic 27% • Joint pain 8.9% • Other muscle pain 7.7% • Unknown 3.6%

  4. Pain caused by a painful stimulus Pain initiated or caused by a primary lesion or dysfunction in the nervous system What is neuropathic pain? Nociceptive Pain Neuropathic Pain

  5. Features of neuropathic pain (1) • Continuous burning pain • Intermittent lancinating or shooting pain • Electric shock-like pain • Nearly always has sensory deficit or distortion

  6. FEATURES OF NEUROPATHIC PAIN

  7. Features of neuropathic pain (2) • Paresthesias: abnormal; spontaneous, intermittent, painless • Dysesthesia: abnormal; spontaneous or touch-evoked, unpleasant

  8. 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

  9. State of normosensitivity Low intensity stimulation High intensity (noxious) stimulation Innocuous sensation PAIN

  10. State of hypersensitivity – spontaneous pain Low intensity stimulation High intensity (noxious) stimulation Innocuous sensation PAIN INCREASED PAIN (Allodynia) (Hyperalgesia)

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

  12. Physiology of nociception Noxious stimulus Response DRG Pain neuron “Soup” of inflammatory agents (histamine, serotonin, prostaglandins, bradykinin) PNS CNS

  13. Peripheral Sensitization

  14. Ectopic Impulses

  15. Central Sensitization Glutamate PresynapticMembrane SubstanceP Ca+2 PostsynapticMembrane NK-1 NMDAReceptor(Depolarized) AMPAReceptor Ca+2

  16. Reorganization of Ab fibers

  17. 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

  18. Loss of Inhibitory Controls Local Descending To brain NORMAL Dorsal horn neuron Local Descending To brain INJURED Exaggeratepain response Innocuous ornoxious stimulus Woolf, 1999.

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

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

  21. 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)

  22. Chronic pain postop • Phantom pain 30-80% • Thoracotomy >50% • Breast surgery • Scar 11-57% • Phantom 13-24% • Cholecystectomy 3-56% • Hernia repair 0-27% Perkins, Kellett. Anaesthesiology 2000;93:1123-2236

  23. 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

  24. 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

  25. 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

  26. 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

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

  28. 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.

  29. Phantom pain. Started on amitriptyline. Gabapentin added later. Pain improved.

  30. Neuropathic pain: Pharmacologic Therapies • Anticonvulsants (gabapentin) • Antidepressants (amitriptyline) • Opioid analgesics (methadone) • Local anaesthetics (lignocaine) • Alpha-2 adrenergic agonists (clonidine) • NMDA receptor antagonists (ketamine) • NSAIDS

  31. Interventional procedures

  32. Spinal cord stimulator

  33. Pain Behaviour Suffering Pain Nociception External factors Loeser & Cousins 1990

  34. PHYSICAL SUFFERING PSYCHOSOCIAL EMOTIONAL SPIRITUAL

  35. Neuropathic Pain: Management • Rehabilitative approaches • physiotherapy • Psychologic intervention • cognitive behavioural therapy (CBT)

  36. Neuropathic pain: Management • Pharmacotherapy • Interventional • Physiotherapy • Psychological • MULTIDISCIPLINARY • BIOPSYCHOSOCIAL

  37. 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

  38. 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

  39. 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

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