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The classification of pain falls into three different categories which include:
Pain is defined as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage" (International Association for the Study of Pain, Subcommittee on Taxonomy, 1979). Pain is always subjective - meaning that it is what the patient describes and it cannot be measured analytically with an objective tool.
Pain is temporally classified as either acute or chronic in nature.
An example of acute pain would be an ankle sprain. The cause and onset is well defined and the duration of pain is limited.
For chronic pain, however, the time of onset is poorly defined and the cause of the pain can be numerous. The duration of the pain can be cyclical and irreversible.
Chronic pain is further subdivided in to two classes: Chronic Malignant Pain (CMP) and Chronic Nonmalignant Pain. An example of CMP would be pain caused by a tumor invading surrounding tissues. An example of chronic nonmalignant pain would be pain due to pressure ulcers or bed sores.
Pathophysiological Classification of Pain
Under this category, pain is divided into two types: nociceptive pain and neuropathic pain.
Nociceptive Pain includes somatic and visceral pain. These types of pain are directly caused by the stimulation of pain nerve endings due to tissue injury or tumor infiltration.
Somatic pain is often described by patients as dull or aching pain. Patients are also able to point directly to the pain as the location is well defined. Common causes of somatic pain include cancer metastasis to the bones or muscles, or mouth blisters (mucositis) due to chemotherapy drugs. Visceral pain is described as throbbing or gnawing in quality. The pain is difficult to locate and the site may be actually distant from the source of the pain. Visceral pain may be caused by liver metastasis causing obstruction or distention of ducts leading to major organs.
Neuropathic pain results from the damage of nerve endings rather than stimulation of nerve endings. Patients describe this type of pain as sharp, numbing, burning, or shooting in quality. This type of pain may be seen in patients with poorly controlled diabetes or shingles (infection with herpes zoster - chicken pox). In the cancer patient, this type of pain may be due to cancer metastasis to the spinal cord.
Etiological Classification of Pain
The etiological classification of pain characterizes pain in terms of the cause of the pain. For example, the cause of pain may be due to tumor infiltration, debilitating disease, or the treatment of the disease itself.