Report 5 of the Council on Science and Public Health (A-06)

Neuropathic Pain

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Summary

Objective:  To review the neurobiology of nociceptive pain and neuropathic pain states, and the definition, classification, typical causes, diagnostic approach, and pharmacologic treatment of neuropathic pain. 

Methods:  English-language reports on studies using human subjects were selected from a MEDLINE search of the literature from 1995 to 2006 using the search terms neuropath*, in combination with pain, treatment, or pathophysiology. In addition, the Cochrane Central Controlled Trials Register was searched using the term pain, in combination with neuropathic or neuropathy and antidepressant, anticonvulsant, or antiepileptic, as well as 26 individual drug names from these and other classes.  A total of 706 articles were retrieved for analysis. Articles were selected for their ability to supply information about the pathogenesis of neuropathic pain or if they represented randomized controlled trials.  When high-quality systematic reviews and meta-analyses were identified, they formed the basis for summary statements about treatment effectiveness.  These reviews were supplemented with an updated literature search.  Additional articles were identified by manual review of the references cited in these publications. Further information was obtained from the World Wide Web sites of the American Pain Society (www.ampainsoc.org), American Academy of Pain Medicine (www.painmed.org), and American Academy of Pain Management (www.aapainmanage.org).

Results:  Nociception is the perception of noxious stimuli.  Acute pain caused by a noxious stimulus is mediated by a specialized, high-threshold neuronal array, the nociceptive system. With tissue damage, trauma, or injury to peripheral nerves, spinal cord, or other central structures, several adaptive mechanisms involving primary afferent receptors, their cell bodies, and other central neurons modulate the nociceptive pain process, and cause various neuropathic pain symptoms and syndromes.  Antidepressants, antiepileptics, local anesthetics, and opioids are currently the most well studied treatments. These agents offer partial relief of peripheral neuropathic pain, but are generally less effective in central pain syndromes. A variety of other interventional techniques are available.

Conclusion: Neuropathic pain is distinct from normal, nociceptive pain triggered by noxious stimuli.  Nociceptive pain serves as an alerting/warning mechanism to decrease further harm.  Neuropathic pain states are triggered by persistent nociceptive stimuli or frank nerve injury.  These conditions activate a series of adaptive and eventually, maladaptive, changes in the function and properties of pain-carrying fibers and other sensory neurons, including phenotypic changes and alterations in gene expression, as well as the fundamental properties of specific neurons and sensory pathways.  Effective management often requires a biopsychosocial approach.  Comprehensive treatments aim to eliminate maladaptive pain-related behaviors, achieve pain control, and improve coping through use of an interdisciplinary team approach to improve psychological functioning, reduce disability, and achieve rehabilitation. Nonpharmacologic approaches include ice massage, heat or ultrasound therapy, relaxation techniques with biofeedback, exercise, massage, hypnosis, transcutaneous electrical nerve stimulation (TENS), physical therapy, acupuncture, or other ancillary techniques.  Cognitive, rehabilitative, behavioral, and, at times, invasive neuromodulatory or neurosurgical interventions may be needed as well.  Despite recent advances in understanding of the pathology related to nervous system injury, the pharmacologic management of neuropathic pain states remains a challenge. 

RECOMMENDATION

The following statement, recommended by the Council on Science and Public Health, was adopted by the AMA House of Delegates as an AMA Directive at the 2006 AMA Annual meeting:

The AMA will disseminate this report to physicians, patients, payers, legislators, and regulators to increase their understanding of issues surrounding the diagnosis and management of maldynia (neuropathic pain).  (Directive)

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