Pain in its many forms is one of the major reasons we seek medical attention. Over 65 million Americans suffer from painful illnesses every year, and over 90% of all illnesses are first noticed because of pain. Chronic pain can lead to depression, interpersonal problems, decreased productivity, and unemployment.

Pain may arise from a discrete cause, such as postoperative pain or pain associated with a malignancy, or it may be a syndrome in which pain is the primary problem, such as neuropathic pains or headaches. The diagnosis of painful syndromes relies on the interpretation of patient history; review of laboratory, imaging and electrodiagnostic studies; occupational and avocational assessments; and physical examination.

Acute pain is an alert that something is wrong within the body. It protects the body from further damage and thus can be beneficial. When pain does not resolve after medical treatment and is prolonged, it no longer serves a protective function. Chronic pain is a complex medical condition that refers to pain that has lasted beyond the expected time for a particular disease, syndrome, or injury. Such pain can be caused by a variety of conditions including crush injury, nerve or spinal cord injury, spinal cord lesions, or lesion and/or injury to the brain. It is frequently severe enough to limit a person's activity and make it difficult to function at work or at home. To further complicate matters, a variety of psychological and behavioral changes occur in patients with long-standing pain.

Chronic pain can occur long after nerve and tissue damage has apparently healed. In this situation pain seems to come from an injury that is not really there. It is a problem caused by pain nerves incorrectly telling the brain that a severe injury is present. The result is severe pain without an injury to cause it. Nonetheless, the pain signals sent to the brain make the pain very real to the person experiencing it. Chronic pain can result in severe mental stress and sometimes major behavioral changes or depression. These problems sometimes result in patients becoming so depressed that they are not able to work or carry on activities of daily living.