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NEUROPATHIC PAIN

NEUROPATHIC PAIN. Dr. Mike Bennett Senior Clinical Lecturer in Palliative Medicine St. Gemma's Hospice and University of Leeds. In the next 40 minutes:. Definitions and mechanisms a refresher Identification the LANSS Pain Scale Therapeutics what’s new? . Definitions.

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NEUROPATHIC PAIN

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  1. NEUROPATHIC PAIN Dr. Mike Bennett Senior Clinical Lecturer in Palliative Medicine St. Gemma's Hospice and University of Leeds

  2. In the next 40 minutes: • Definitions and mechanisms • a refresher • Identification • the LANSS Pain Scale • Therapeutics • what’s new?

  3. Definitions Neuropathic pain is: Pain due to a disturbance of function or pathological change in a nerve Merskey 1986 Pain in an area of abnormal or absent sensation Glynn 1989 The distribution of pain with associated sensory abnormalities that jointly and in a clinical context point to a neurological condition Hansson 1996

  4. Definitions • Neuropathic pain is the preferred term • neurogenic or deafferentation terms are confusing • Neuropathic pain can arise : • peripherally = peripheral nerves and posterior roots • centrally = spinal cord and brain

  5. Mechanisms • Peripheral • nociceptor sensitization • abnormal axonal responses • Central • disinhibition • hyperexcitability

  6. Identification • Positive phenomena • Spontaneous pains • Continuous • Cutaneous, deep, visceral • Paroxysmal • Evoked pains • Quantitative - hyperalgesia • Qualitative - allodynia • Temporal - hyperpathia • Spatial - radiation, dyslocalisation

  7. Identification • Negative phenomena • impaired soft touch, pin-prick and thermal sensibility • Autonomic features • Vasomotor • Sudomotor

  8. Identification LANSS Pain Scale • 5 symptom groups • Dysaesthesias (5) • Autonomic changes (5) • Evoked pain (3) • Paroxysmal (2) • Thermal sensations (1) • 2 sensory examination items • Allodynia (5) • Altered PPT (3) Bennett Pain 2001

  9. Summary of LANSS Pain Scale • Assesses the probability that neuropathic mechanisms contribute to the patient’s pain experience • Reliable and validated scale that provides immediate clinical information • emphasises relative dominance of neuropathic mechanisms

  10. Therapeutics • ‘An area of clinical practice marked more by polarised views and contention than consensus’ • Frequent treatment failure • inadequate titration • early termination

  11. TherapeuticsKarolinska Institute audit • Audit of 153 cancer patients in major hospital • 61% had pain, VAS 2.4-6.6 • Problems • lack of pain diagnosis • failure to detect neuropathic pain components • under dosing of opioids Arner et al, Lakartidningen 1999

  12. TherapeuticsWHO guidelines • 593 cancer pain patients surveyed • Treatment based on opioids +/- adjuvants • 36% of patients had neuropathic component • 5% pure and 31% mixed • no more intense than nociceptive group • 96% had opioids • 53% had adjuvants • VAS decreased from 70mm to 28mm Grond et al, Pain 1999

  13. TherapeuticsOpioid responsiveness • is satisfactory analgesia without un-manageable side-effects after dose titration • is a continuum determined by • patient, pain and drug related factors • Neuropathic pain reduces responsiveness • but does not confer resistance Bruera 1989, Portenoy 1994

  14. TherapeuticsOpioids • Intrathecal route less effective for neuropathic pain than nociceptive pain? • 43 cancer pain patients Nociceptive Neuropathic Patients : 23 20 Duration of treatment: 5 months 2.5 months Initial mean reduction in pain: 77% 61% Continuing mean pain reduction: 66% 11% Becker et al, Stereotactic F Neurosurg 2000

  15. TherapeuticsFentanyl • IV fentanyl v active placebo • 48 patients with NP • Significantly more relief with fentanyl • But less impressive follow up with patch • 13/48 had ‘substantial relief’ (correlate with IV) • 5/48 had moderate relief • so 30/48 had no relief or side effects (18 withdrew) Dellemijn et al, Lancet 1997, JPSM 1998

  16. TherapeuticsAlfentanyl • 12 patients with NP - post nerve injury • IV alfentanyl vs ketamine vs active placebo • alfentanyl similar to ketamine • significantly better than placebo • dose dependent reduction in spontaneous and evoked pains • suggestion of both peripheral and central mechanisms Leung et al, Pain 2001

  17. TherapeuticsOxycodone • 38 patients with PHN • Oxycodone vs inactive placebo, 4 weeks each • All patients had stable doses of adjuvants • 22/38 better on oxycodone (7/38 placebo) • significant reduction in spontaneous and evoked pain Watson and Babul, Pain 1998

  18. TherapeuticsOpioids with NMDA activity • Dextromethorphan • 60 cancer pain pts • WHO (no adjuvants) vs WHO + DM • no advantage with DM • no difference between nociceptive and neuropathic pain responses Mercadante et al JPSM 1998

  19. TherapeuticsOpioids with NMDA activity • Methadone • Hypothesis - if NMDA activity important, then less methadone needed in NP after switching from morphine or hydromorphone • 34 cancer pain patients - 22 with NP • no difference in ratios between two groups Gagnon and Bruera JPSM 1999

  20. TherapeuticsVenlafaxine • ‘Cleaner amitriptyline’ • 16 volunteers studied • 4 doses of 37.5mg v placebo • Laboratory pain tests • Significant effects for venlafaxine • increased tolerance for electrical nerve stimulation and pain summation (rpt stimuli) Enggaard et al, Clin Pharm Therap 2001

  21. TherapeuticsAntiepileptics • Gabapentin • 2 important studies with 390 patients • significant benefit in DN and PHN • Topiramate • 3 blinded studies • no benefit in DN Rowbotham et al JAMA 1998, Backonja et al JAMA 1998

  22. Lamotrigine (glutamate antagonist) • Refractory TN • 11/13 patients preferred it over placebo • used as add on to carbamazepine or phenytoin • Spinal cord injury • 22 patients, no overall effect • but incomplete SCI - reduced evoked pain Zakrzewska et al Pain 1998 Finnerup et al Pain 2002

  23. TherapeuticsAntiarrhythmics • IV Lidocaine • substantial body of evidence now for efficacy • difficult to maintain effects • Topical lidocaine patch • effective at local and central levels • 25 / 32 PHN pts benefited (compared to 3 /32 on placebo) Galer et al Pain 1999

  24. TherapeuticsAntiarrhythmics • Mexiletine • earlier evidence of effectiveness 1988-1997 • 216 DN patients (675 mg daily) • 11 peripheral nerve injury pts (750mg daily) • 95 DN pts (450 mg daily)

  25. TherapeuticsAntiarrhythmics • but growing evidence of ineffectiveness 1998-2002 • spinal cord injury • HIV neuropathy • heterogenous NP • capsaicin induced pain • cancer pain (not NP)

  26. TherapeuticsKetamine • Many small studies supporting efficacy • Adverse effects limit its use • Oral route may be better tolerated • In cancer pain • 10 /10 patients benefited from IV bolus, 6 had side effects • enhanced opioid analgesia in neuropathic pain Mercadante et al JPSM 2000

  27. TherapeuticsCCK antagonists • CCK • is an anti-opioid peptide • diminishes opioid sensitivity via CCK receptors • In inflammatory states • actions of spinal morphine increased as CCK activity is reduced • In neuropathic pain • up-regulation of CCK • reduced response to opioids

  28. TherapeuticsCCK antagonists • Devacade vs placebo • IV and oral dosing studies • 41 NP patients • significant benefit over placebo Simpson et al 2002 (in press)

  29. TherapeuticsCannabis • No specific study in NP • Systematic review of all chronic pain • including cancer and neuropathic pain • No more effective than codeine • more adverse effects • ‘Further trials needed before use in spasticity or NP’ Campbell et al BMJ 2001

  30. TherapeuticsMagnesium • Blocks NMDA receptor • Mg might reduce wind-up • Observational study, Mg infusion • 12 cancer pain patients • well tolerated • overall: 4 complete relief, 6 partial, 2 none Crosby et al JPSM 2000

  31. NNTs and all that • Useful measure • Note that ‘50% pain relief’ can mean: • 50% reduction in VAS where measured • ‘excellent or good’ relief • but also ‘moderate’ relief • Confidence intervals of NNTs important too • SSRIs 6.7 (3.4 - 435) • Don’t forget NNH

  32. NNTs and all that • WHO ladder • oxycodone 2.5 (1.6-5.1) • Tricyclics • amitriptyline group 2.0, NNH 3.7 • Antiepileptics • gabapentin NNT 3.5, NNH 2.5 • or carbamazepine better? (NNT 2.3, NNH 3.7)

  33. Neuropathic pain and cancer • The difference is in the patient not the pain • more frail • changing pain picture • additional renal, hepatic or cognitive impairment • Toxicity may be reached before benefit • NNT may be higher and NNH may be lower in this group

  34. A therapeutic approach A. Initial steps 3. GABAPENTIN [add in or replace] 2. AMITRIPTYLINE [add in or replace] 1. W.H.O. LADDER

  35. A therapeutic approach B. Advanced steps ‘The unlit loft at the top of the ladder’ 6. METHADONE 5. ANAESTHETIC APPROACHES 4. KETAMINE [with opioid]

  36. Summary • Assess thoroughly • remember taxonomy and clinical features • Use a total pain model • Prescribe sensibly • evidenced based, up the ladder and monitor side effects • Seek advice if it’s going pear shaped

  37. Thank you m.bennett@st-gemma.co.uk

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