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A systematic search of the medical literature was performed in April and May of 2006. The search, limited to human subjects, and English language journals included the Cochrane database, PubMed, and the National Guideline Clearinghouse.

Pain is a common reason for individuals to seek medical care. In 2003, three of the 20 most frequently mentioned reasons for outpatient department visits in the United States were related to stomach, head, or back pain.1 Similarly, in a 1998 study, 21.5% of persons in a multinational sample across Asia, Africa, Europe, and the Americas reported pain most of the time during the previous 6 months.2 In a study of more than 46000 European and Israeli persons, the prevalence of chronic pain ranged from 12% to 30%, with a weighted average of 19%.3 In the United States, pain is often suboptimally treated in persons of all ages and a wide variety of conditions.4–12 Important clinical, human, and economic consequences of this shortcoming include altered immune-system functioning, diminished ability to function, increased risk of chronic pain, needless suffering, and higher healthcare costs.13–22 In the United States, 2002 costs of lost productive time caused by pain have been estimated at $61.2 billion.23 A sample of individuals with neuropathic pain disorders incurred charges of more than $17000 during calendar year 2000 compared to approximately $5715 in a matched control group without neuropathic pain.24 An analysis of symptomatic diabetic peripheral neuropathy and its associated complications found that 2001 costs were approximately $237 million.25

Terms used to define and describe pain are emotionally charged and often used incorrectly or unclearly. As a result, it is important to begin discussions of pain by building a foundation of commonly agreed upon terms and concepts. A simplified taxonomy of pain follows; the reader is referred to the International Association for the Study of Pain for a more complete list.26 Pain is a subjective, unpleasant, sensory, and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. More simply put, “pain is what the person says it is, existing whenever he says it does.”27 The core of these definitions is that pain is subjective, has multiple dimensions, without a clear relationship between the intensity of the sensation and tissue damage.28 Clinicians also need to be aware that individuals may have pain even if communication is difficult or impossible. Because pain is a subjective experience, it is critically important that patients’ reports of pain be taken seriously.26

Pain is commonly described in terms of duration (e.g., acute or chronic) and pathophysiology (e.g., nociceptive or neuropathic). These constructs can be helpful, suggesting treatments that are likely to be effective, but they can also be misleading. For example, acute pain is often described as being of recent onset and limited duration, with a tendency to decrease over time, while chronic pain is often described as ...

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