Typically this can be done due to duration, pathogenesis, location and cause but this distinct categorization does not appreciate that severe chronic pain is multifactorial in nature. Therefore, new approaches meet the complexity of pain.1
Classification according to duration
Acute pain is a part of the body's protective system. It acts as a warning signal of imminent or actual damage. In this respect pain has an important function in maintaining or restoring physical integrity.
However, pain may also be experienced occasionally in the absence of any tissue damage, and its intensity may not be in proportion to the original injury. This is called chronic pain.
This means: Acute and chronic pain do not only differ in duration, that is hours and days versus months, but also in the underlying pathophysiological mechanism.
Classification according to pathogenesis
Pain that is caused by the presence of a painful stimulus on nociceptors is called nociceptive pain. Nociceptive pain in its acute form usually serves an important biological (or evolutionary) function as it warns the organism of impending danger and informs the organism of tissue damage or injury.
Pain initiated or caused by a primary lesion or dysfunction in the nervous system is called neuropathic pain. Neuropathic pain occurs as a result of damage to the nerve fibres with the pain impulse emanating from the neuronal structures themselves, rather than from stimulated nerve endings. However, the pain is projected into the region supplied by the nerve ("projected pain"). Some of the most baffling types of chronic pain, such as diabetic neuropathy, phantom limb pain and post-herpetic neuralgia are neuropathic in origin. A significant proportion of patients suffering from chronic low back pain or cancer pain have in addition to a nociceptive part, also a neuropathic component.
Psychogenic pain is caused by the mental processes of the sufferer rather than by immediate physiological causes. Purely psychogenic pain is rare, and its incidence is often overestimated. Nevertheless, chronic pain frequently has a secondary psychological component resulting in a mixed presentation (e.g. psychosomatic pain).
Classification according to location
Pain can be also classified according to its location, e.g. abdominal or back pain.
Locations of chronic pain restricting daily activity
(% of total sample saying they have experienced pain in location for 3 months or longer)
The 2007 Eurobarometer2 report revealed the most common locations for chronic pain that restricts daily activities.
Classification according to cause
Patients experience pain for various reasons. It can be caused by e.g. due to surgical procedures, arthritis, degeneration of joints, bones or nerves, tumors or overstraining of muscles.
The most frequent reasons why patients suffer chronic pain are osteoarthritis, back pain and cancer related pain.
1 Korff M, Dunn KM. Chronic pain reconsidered. Pain. 2008; 138(2):267–276.
2 European Commission Health in the European Union: Special EUROBAROMETER 272, 2007. http://ec.europa.eu/health/ph_publication/eb_health_en.pdf