Differentiating Neuropathic Pain

Through Appropriate Assessment and Diagnosis

Contents

• Introduction
• Defining the Problem
• Common and Costly*
• The Presentation of Neuropathic Pain*
• Invisible Hurt: The Pathophysiologyof Neuropathic Pain*
• Peripheral Mechanisms*
• Ion Channels and Neuropathic Pain*
• Neuronal Damage and Regeneration*
• Central Mechanisms*
• Central Sensitization*
• Sympathetically Maintained Pain*
• Diagnosis and Assessment*
• Patient History*
• Physical and Neurological Examination*
• Pain Assessment Instruments*
• Other Investigations*
• Diagnosing Neuropathic Pain: Case Studies*
• Case Study 1*
• Case Study 2*
• Summary*
• References*
• Additional Information*

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Target Audience

Physicians, nurses, and pharmacists

Purpose Statement

The purpose of this monograph is to increase the knowledge of assessment and diagnosis of neuropathic pain.

Learning Objectives

After completing this activity, participants will be able to:

• Differentiate between neuropathic pain and other pain types
• Summarize appropriate assessment and diagnosis techniques used to distinguish neuropathic pain from other chronic pain types
• Apply an understanding of neuropathic pain mechanisms to promote rational therapeutic selections for neuropathic pain conditions

Introduction

Pain is usually a consequence of tissue injury and generally resolves once the injury heals. For some individuals, however, pain may be present in the absence of injury or persist long after the injury has healed. Such pain is likely neuropathic in origin, reflecting abnormal transmission of pain signals by the central or peripheral nervous system.¹ Neuropathic pain is very common in primary care and pain clinics, affecting over 4 million individuals in the United States alone.²

Rather than a single entity, neuropathic pain is a diverse collection of pain syndromes unified by the presence of an underlying nerve injury or dysfunction.¹ This diversity is reflected both in the many conditions associated with neuropathic pain–ranging from diabetes to multiple sclerosis to poststroke pain–and in the various classes of medication used to treat neuropathic pain.

Diagnostic and treatment challenges arise from this complexity. Traditional analgesics, such as the nonsteroidal antiinflammatory drugs (NSAIDs), are generally not as successful in providing relief from neuropathic pain, whereas nontraditional agents, such as certain anticonvulsants, have demonstrated efficacy in some patients.^2-4 Nevertheless, patients are often inappropriately treated with agents that are typically ineffective in neuropathic pain, leaving many with ongoing symptoms.^4-6 Reasons for poor management of neuropathic pain may include inaccurate diagnosis and assessment and a limited understanding of the pathophysiology of neuropathic pain syndromes.⁴ This tutorial reviews evidence-based approaches to diagnosis and assessment, as well as the latest understanding of pathophysiological mechanisms underlying neuropathic pain.

Defining the Problem

The International Association for the Study of Pain (IASP) has defined neuropathic pain as “pain initiated or caused by a primary lesion or dysfunction of the nervous system.”² Some investigators have challenged this definition, particularly the use of the term “dysfunction,” which they criticize as vague.⁷ This term, some have argued, may confound the differentiation of neuropathic pain from other pain mechanisms, such as inflammatory pain.⁷ Until the various mechanisms of neuropathic pain are better understood, however, a definitive description may remain elusive. One proposed compromise is to define neuropathic pain as “pain caused by a lesion of the peripheral or central nervous system (or both) manifesting with sensory symptoms and signs.”^2,7

The distinction may appear academic. An article describing neuropathic pain, however, points out that improving the definition of neuropathic pain contributes to greater specificity of pain diagnoses. An accurate diagnosis enables the selection of appropriate treatment, which, in the case of neuropathic pain, is likely to be an agent not normally used for other types of pain. A strong and specific definition also prevents clinicians from diagnosing any pain of uncertain origin as neuropathic, whether it is neuropathic or not.⁷

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