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.
Over 100 million Americans suffer chronic pain  and roughly 63 percent of pain sufferers seek help from their primary care clinicians . Pain accounts for 20 percent of outpatient visits and 12 percent of all prescriptions . 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 [4,5].
Persistent pain often causes functional impairment and disability, psychological distress (anxiety, depression), and sleep deprivation . 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 .
Pain is the most common cause of long-term disability, with lost work days in the United States estimated at more than 50 million days per year . The annual cost of untreated or undertreated pain to taxpayers and employers has been calculated at over $100 billion per year, in direct and indirect expenses . The use and misuse of opioids for management of chronic pain is a major concern, with problems arising from their multiple adverse side effects including drug-dependency, from drug diversion, and from undertreatment of chronic pain symptoms for fear of narcotic abuse. Chronic pain is thus a major medical and social issue.
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.