Continuum, Neuropathic Pain, October 2009, Volume 15, Issue 5

Neuropathic pain is more prevalent in neuropathies associated with prominent involvement of the small unmyelinated and lightly myelinated nerve fibers (the C and A[delta] nerve fibers). However, it is not unusual to find neuropathic pain in patients with mixed large-fiber and small-fiber neuropathies and even in neuropathies with predominantly large-fiber involvement. Peripheral neuropathic pain may occur in generalized polyneuropathies, focal peripheral neuropathies (eg, postherpetic neuralgia), mononeuritis multiplex, segmental neuropathies (eg, brachial neuritis), and radiculopathies. Pain results in a substantial proportion of the morbidity associated with a generalized polyneuropathy. This chapter will cover the diagnosis and assessment of the most common and clinically important generalized polyneuropathies that cause neuropathic pain.(C) 2009 American Academy of Neurology

Complex regional pain syndrome (CRPS) is clinically characterized by pain, abnormal regulation of blood flow and sweating, edema of skin and subcutaneous tissues, active and passive movement disorders, and trophic changes. It is classified as type I (reflex sympathetic dystrophy) and type II (causalgia). CRPS cannot be reduced to one system or to one mechanism only. Changes in somatosensory systems processing afferent information in sympathetic systems and in the somatomotor system indicate that the central representations are altered. Edema, inflammation, and sympathetic-afferent interaction (sympathetically maintained pain) point to peripheral abnormalities. Treatment of the individual patient is empiric, mainly using evidence-based techniques that have been proven to be effective in other neuropathic conditions. Treatment should be immediate and most importantly directed toward restoration of full function of the extremity. This objective is best attained in a comprehensive interdisciplinary setting with particular emphasis on pain management and functional restoration.(C) 2009 American Academy of Neurology

Opioids have demonstrated efficacy in relieving neuropathic pain. Familiarity with the pharmacology and adverse effect profile of this class of medication is essential for its safe and optimal use, as is knowledge of the regulatory requirements related to opioid prescribing. Opioids are versatile and can be effective as part of a rational multidrug therapeutic approach. As such, they are an integral part of the multimodal and multidisciplinary treatment of neuropathic pain.(C) 2009 American Academy of Neurology

Chronic pain is a multifaceted disease requiring multimodal treatment. Clinicians frequently prescribe various combinations of pharmacologic, interventional, cognitive-behavioral, rehabilitative, and other nonmedical therapies, even in the absence of high-quality evidence in support of such an approach. Therapies are often selected consistent with the biopsychosocial model of chronic pain, reflecting the complex nature of the patient's report of pain and the myriad factors that influence it. Elucidating mechanisms that govern normal sensation in the periphery has provided insights into the biochemical, molecular, and neuroanatomic correlates of chronic pain, an understanding of which is leading increasingly to efforts to provide mechanism-specific multidrug therapies. Peripheral and central neuroplastic reorganization underlying the disease of chronic pain is influenced by patient-specific emotions, cognition, and memories, further impairing function and idiosyncratically defining the illness of chronic pain. Clinical perceptions of these and related subjective elements associated with the suffering of chronic pain drive psychosocial treatments, including, among other options, relaxation therapies, coping skills development, and cognitive-behavioral therapy. Treatment selection is thus guided by comprehensive assessment of the phenomenology and inferred pathophysiology of the pain syndrome; patient goals, preferences, and expectations; behavioral, cognitive, and physical function; and level of risk. Experiential, practice-based evidence may be necessary for improving patient care but is insufficient; well-designed studies are needed to support therapeutic decision making. This review will discuss the biochemical basis of pain, factors that govern its severity and chronicity, and foundational elements for current and emerging multimodal treatment strategies.(C) 2009 American Academy of Neurology