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Definition and pathogenesis of chronic pain

Ellen WK Rosenquist, MD
Section Editor
Mark D Aronson, MD
Deputy Editor
Marianna Crowley, MD


Pain is one of the most common and debilitating patient complaints, affecting individual patients, their friends and families, the work force, and society in general.

Research efforts in understanding pain range from the molecular biology of nociceptive pathways to the psychosocial aspects that influence the experience of pain. Although such studies have resulted in significant strides in pain management and quality of life for patients with persistent pain, the evaluation and treatment of pain remains suboptimal.

An overview of the definition, classification, and pathogenesis of chronic pain is presented here. The evaluation of patients presenting with chronic pain, the general therapeutic principles of chronic pain, and specific pain syndromes are discussed separately. (See "Evaluation of chronic pain in adults".)


Over 100 million Americans suffer chronic pain [1,2] and roughly 63 percent of pain sufferers seek help from their primary care clinicians [3]. Pain accounts for 20 percent of outpatient visits and 12 percent of all prescriptions [4]. Patients with symptoms of chronic pain are seen by clinicians in multiple clinical settings. Most patients who present with pain complaints rate their symptoms as moderate to severe [5,6]. One survey from 2010 estimated that 19 percent of adults in the United States report constant or frequent pain persisting for at least three months [7].

Persistent pain often causes functional impairment and disability, psychological distress (anxiety, depression), and sleep deprivation [8]. Almost 80 percent of chronic pain patients report that pain disrupts their activities of daily living, and two-thirds indicate that pain has negatively impacted personal relationships [9].


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Literature review current through: Aug 2017. | This topic last updated: Jan 09, 2015.
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