Pain is classified in several ways, including the familiar categories of acute and chronic. For example, pain can be classified based on its temporal aspects, its etiology and its associated features from differing sources, and its functional significance (see Table 2-5). Acute pain has been customarily defined as pain that is less than 6 months in duration. Chronic pain is defined as pain persisting beyond 6 months (Crue 1983). There are always problems with arbitrary definitions such as these. For example, it becomes difficult to classify some painful conditions (e.g., migraine or osteoarthritis) based on temporal aspects. Migraine is a recurrent painful disorder that can persist for years, but the specific episodes ofpain are relatively short-lived. Osteoarthritis, on the other hand,
Table 2-5. Features distinguishing acute and chronic pain
Acute pain Chronic pain
Duration <6 months >6 months
Cause Tissue damage, injury, Pathophysiologic processes inflammation in the peripheral or
CNS pathways Psychogenic factors
Biological utility Yes No
Psychological factors No Yes contributing
Note. CNS = central nervous system.
is a chronic, progressive medical condition that is accompanied by a mixture of acute and chronic pain components. Acute pain can be precipitated by new injury, whereas chronic pain features can arise from prior injuries and sensitization of peripheral nervous system involvement.
Generally, acute pain is considered to be pain that serves self-protective functions. The value of the alarm functions of pain brought on by the inadvertent slamming of one's thumb with a hammer is obvious. Such pain, it is hoped, is discrete and mobilizes the person to take measures to minimize pain and prevent further injury. Conversely, chronic pain is considered to have lost such meaningful aspects. One is hard-pressed to arrive at any adaptive function gleaned from chronic neuropathic pains or fibromyalgia.
Acute pain arises from tissue injury, trauma, or inflammation. Chronic pain extends beyond the period of healing and can be brought on by pathophysiologic processes within the nervous system. Some pain states can be mediated by the ongoing barrage ofperipheral pain sensors (i.e., nociceptors). The pathologic firing of peripheral or CNS pathways that mediate pain can also trigger chronic pain.
Another distinction between acute and chronic pain states is based on the presence of psychological and psychiatric conditions that accompany or aggravate the pain. The pain brought on by fracture or another traumatic injury is not necessarily accompanied by the personality changes and psychiatric disturbances that can accompany chronic pain states. Psychological sequelae of acute pain are likely to be discrete and obvious.
The long duration and pervasive effects of chronic pain states likely have an impact on a person's functioning. Naturally, pain can have profound effects on social, interpersonal, and emotional functioning. By virtue of the long-term course, there may be changes in mood, thought patterns, perceptions, and personality that accompany the pain. One's life experiences and ability to adapt to ongoing demands and stress are affected. Therefore, it is incomprehensible to address chronic pain without considering psychological and social functioning.
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