Neuropathic Pain Scott Magnuson, MD Pain Management of North Idaho, PLLC
Pain is our friend "An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." Early warning system
Acute vs Chronic Pain Characteristic Acute Pain Chronic Pain Cause Usually known Often unknown Persists after Duration Self-limited healing; >/= 3 months Treatment Resolution of underlying cause Treat underlying cause & pain disorder
Impact of Chronic Pain Quality of Life Physical function Ability to do ADLs Work Recreation Social consequences Marital/family Intimacy Social isolation Psychological Morbidity Depression Anxiety, anger Sleep disturbance Loss of self esteem Socioeconomic Consequences Healthcare costs Disability Lost workdays
Definition of nociceptive and neuropathic pain Nociceptive = pain caused in response to potentially tissue damaging stimuli Neuropathic = pain caused by a primary lesion or dysfunction in the peripheral or central nervous system
Examples of Nociceptive and Neuropathic Pain
Pain Pathways
Primary Afferent Axons A-alpha A-beta A-delta C Mechanoreceptors Sensory/ fast pain Multimodal sensory/slow 13-20 6-12 1-5 0.2-1.5 80-120 35-75 5-35 0.5-2 Mechanoreceptors/ proprioception Diameter (um) Speed (m/s) pain
Wind-up
Fig. 2: Neuropathic pain arises following nerve injury or dysfunction. Gilron I et al. CMAJ 2006;175:265-275 2006 by Canadian Medical Association
Evaluation of The Patient Pain intensity 0-10 scale Repeatable & consistent Track progression/ success of tx
Evaluation of The Patient Pain Descriptors Hot Burning Sharp Stabbing Cold Shocking Electric-like Non-painful sensations Tingling Prickling Tingling Itching Pins and needles
Evaluation of The Patient Functional impact Effect of pain on sleep, ambulation, self-care, activities of daily living, work, social or sexual function, mood and suicidal ideation Attempted treatments Determine and document adequacy of dose titration for titratable drugs (e.g., dose reached and duration of treatment, drug treatment stopped owing to adverse effects or lack of efficacy)
Evaluation of The Patient Alcohol or substance abuse Addiction history will affect decision to prescribe opioids Consider earlier involvement with a mental health counselor, psychologist or psychiatrist Consider safety of sedative analgesics with alcohol or other sedatives
Evaluation of The Patient Physical examination Gross motor examination Motor weakness may occur around the involved nerves Attempt to differentiate between true weakness and antalgic weakness Deep tendon reflexes May be diminished or absent around the involved nerves
Sensory Evaluation Light touch, pin prick, vibration sense and proprioception may be diminished or absent in the involved nerve territory Sensory disturbance may aberrantly extend beyond a discrete nerve territory Dynamic allodynia (pain due to cotton wool lightly moving across the skin) Thermal allodynia (burning sensation in response to ice cube on skin) Pinprick hyperalgesia (exaggerated pain following pinprick to the skin) Pain when straight leg is raised, suggestive of irritation of lumbar nerve root Elicitation of myofascial trigger points to favor a diagnosis of myofascial pain over neuropathic pain Possible presence of Tinel's sign
Skin Examination Alterations in temperature, color, sweating and hair growth suggestive of complex regional pain syndrome Residual dermatomal scars consistent with previous herpes zoster (shingles) infection Characteristic skin changes consistent with diabetes mellitus
Causes of Neuropathic Pain Diabetes Traumatic Multiple sclerosis Vitamin deficiencies HIV Medications Herpes Zoster Alcohol Neoplasia Heavy metals
Non-pharmacologic Treatment Options Cognitive-behavioral therapy Meditation Imagery Biofeedback Relaxation therapy Physical Rehabilitation Acupuncture Transcutaneous electrical stimulation
Antidepressants Tricyclics Amitryptyline Nortriptyline Desipramine SSRIs Citalopram, escitalopram, fluoxetine, paroxetine, sertraline SNRIs Duloxetine, venlafaxine, desvenlafaxine
Topical Agents Lidoderm 5% Capsaicin Topical cream OTC/Rx Qutenza Compounded gels/creams Lidocaine, anti-inflammatories, TCAs, ketamine
Anticonvulsants Sodium channel modulators Carbemazepine Phenytoin Voltage dependent Ca++ channel blockers Gabapentin Oxcarbazepine Pregabalin Lamotrigene* Lamotrigene* Topiramate* Topiramate*
NMDA antagonists Ketamine Dextromethorphan
Opioids Short-acting Hydrocodone Oxyodone Morphine Hydromorphone Oxymorphone
Opioids Long-acting Oramorph, MS Contin, Avinza, Kadian Oxycodone SR, OxyContin Fentanyl patch, Duragesic Oxymorphone Methadone
Opioids: Evidence for Neuropathic Pain? Opioids for neuropathic pain. Cochrane Database of Systematic Reviews 2006, Issue 3 Opioids only. No adjunct meds. Short term studies (<24 hrs) = equivocal results Intermediate term (up to 8 weeks) demonstrated improvement
Other Medications Mexiletine Clonidine Dronabinol
Multimodal Analgesia Drug combinations can provide improved analgesia with less side effects Gilron I, Bailey JM, Tu D, et al. Morphine, gabapentin, or their combination for neuropathic pain. N Engl J Med 2005;352:1324-34. Simpson DA. Gabapentin and venlafaxine for the treatment of painful diabetic neuropathy. J Clin Neuromusc Disease 2001;3:53-62.
Trigeminal Neuralgia Carbamazepine Gabapentin Lamotrigene Baclofen
Interventional Pain Management Common nerve blocks Ilioinguinal Common peroneal Agents Local anesthetics Steroids Neurolytics (phenol, alcohol)
Interventional Pain Management Trigeminal nerve block
Interventional Pain Management Sympathetic blocks Stellate Lumbar Superior hypogastric Ganglion impar
Interventional Pain Management Sympathetic blocks Useful for sympathetically mediated pain Series can be beneficial Used in conjunction with PT Cancer patients - Neurolytic
Interventional Pain Management Epidural steroid injections Cervical, thoracic or lumbar Interlaminar, transforaminal Diagnostic, therapeutic
Interventional Pain Management Spinal cord stimulation Useful for radiculopathies/ neuralgias After more conservative therapies have failed No surgical corrective therapies indicated
Interventional Pain Management Intrathecal drug delivery systems Useful when refractory to other conservative txs Combination therapies
Gilron I et al. CMAJ 2006;175:265-275