6/8/2010
Assessment and Management of Neuropathic Pain Amy McDonald MD John Tangeman MD Christopher Kerr MD PhD
Objectives • Define the characteristics of neuropathic pain i • Review the role of opioids as monotherapy for neuropathic pain • Describe adjuvant treatment options for the management of neuropathic pain the management of neuropathic pain • Review a novel approach to treating refractory neuropathic pain
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Neuropathic Pain • Presumed to result from disordered function of p p y the peripheral or central nervous system due to many potential causes – Peripheral • Extopic insult leading to abnormal nociceptors – Diabetic peripheral neuropathy
– Central • Sensitization and reorganization of pain pathways at dorsal horn level – Phantom limb pain
– Sympathetic mediated pain (SMP)‐ leads to sustained neuropathic pain • Alpha‐adrenergic receptors on injured C‐fibers may be a relevant mechanism of SMP, but others are possible – Chronic regional pain syndrome (CRPS)‐ increased likelihood of SMP
Neuropathic Pain: Clinical Symptoms • Neurologic deficits: – numbness numbness – weakness • tripping episodes, inability to open jars
• Neurologic sensory dysfunction: – touch‐evoked pain – intermittent abnormal sensations – spontaneous burning and shooting pains b i d h i i
• Burning, shooting, electrical‐quality pain • May be aching, throbbing, sharp • Neuropathic Sensations
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Neuropathic Pain: Neuropathic Sensations • Neuropathic sensations – Dysesthesias y – Paresthesias
• Paresthesias – – – –
Painless Abnormal (ie: feeling like ants crawling under skin) Spontaneous or evoked by stimulus Intermittent
• Dysesthesias Dysesthesias – Unpleasant – Abnormal – Spontaneous or touch‐evoked
Neuropathic Pain: Evoked Dysesthesias • Allodynia – Pai Pain elicited by a nonnoxious stimulus (clothing, air eli ited by a o o iou ti ulu ( lothi ai movement, touch) • Mechanical (induced by light pressure) • Thermal (induced by a non‐painful cold 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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Case • 58 year old woman with stage IV breast carcinoma with severe left brachial i ith l ft b hi l plexopathy • Taking lortab 5/500 1‐2 qid with ongoing lancinating left arm pain • Treatment options? Treatment options?
Opioids
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Case Continues • MS‐Contin 15mg BID with Lortab 5/500 1‐ 2 q 6 h prn for breakthrough 2 q‐6‐h prn for breakthrough • Transient partial response, pain again escalates to 7‐8/10 • Opioids alone are rarely effective in the management of severe neuropathic pain syndromes d • Patient constipated and somnolent on above regimen
Adjuvant Analgesics: Definition • Drugs that have a primary indication other than pain which are analgesic in th th i hi h l i i specific painful conditions • Often used as first line drugs for pain • Often combined with opioids for better analgesia
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Adjuvant Analgesics • Anticonvulsants • Antidepressants • N‐Methyl‐D‐aspartate (NMDA) receptor antagonists • Corticosteroids • 2adrenergic agonists d • Interventions • Local anesthetics • Topical analgesics
Anticonvulsants • First Generation – – – –
Older agents used in past for pain Olde a e t u ed i a t fo ai Carbamazepine, phenytoin‐ more evidence Valproic acid, clonazepam‐ less evidence Many side effects and drug interactions
• Second Generation – Gabapentin, pregabalin, lamotrigine, topiramate, oxcarbazepine, tigabine, levetiracetam, zonisamide
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Gabapentin (Neurontin®) • Minimally protein bound, excreted unchanged , g in urine and not metabolized in liver, no drug interactions. • Inhibits calcium influx into neurons (calcium channel blocker) diminishing neuronal hyperactivity that has been associated with neuropathic pain • Most patients need at least 900‐3600mg daily to achieve analgesia hi l i • Ceiling effect, low oral bioavailability • Somnolence and dizziness is side effect when at higher doses • Titrate slowly in elderly, reduce dose in renal impaired patients
Gabapentin (Neurontin®) • Proven to be effective in both non‐ malignant and cancer related NP malignant and cancer related NP – DPN, PHN, CPRS, HIV neuropathy, neuropathic cancer pain, MS related pain, trigeminal neuralgia, painful nocturnal spasms • Improved analgesia when paired with p g p morphine than either agent alone h h h l
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Gabapentin (Neurontin®) Starting dose Routine Eld l Elderly, medically frail di ll f il Renal insufficiency (CrCl15 ml/min) Renal failure (CrCl