Causes & Classification of pain

It is important all reasonable attempts have been made to determine the cause(s) of pain in order to select the most appropriate treatment option. Pain is generally discussed in terms of these components5:

  1. Nociceptive pain
  2. Neuropathic pain
  3. Psychogenic pain (See Pain in the absence of a physical cause).

    4. Nociceptive pain
    Nociceptive pain arises from stimulation of superficial or deep tissue receptors (nociceptors) as a result of tissue injury or inflammation5. Nociceptive pain can be subdivided into somatic (superficial and deep) and visceral, according to the origin of the pain stimulus.

    Neuropathic pain
    This is pain due to damage and/or dysfunction to the nervous system, either through injury, disease or localised trauma (e.g. trigeminal neuralgia, post stroke pain, post herpetic neuralgia) [See Assessing neuropathic pain]5.

    Psychogenic pain
    Psychogenic pain is the general term applied to pain of presumed psychological origin, in the context of absence of any discernible organic disease or injury. Alternatively, an organic disorder may be present, but the symptoms experienced are in excess of, or disproportionate to, those usually seen with that level of organic disorder. In this syndrome the psychological dimension is deemed to be predominant and thus to be distinguished from the psychological disturbances resulting from chronic or persistent pain5.

Classification of pain

Pain can also be classified as either acute or chronic5:

Acute pain is nociceptive in origin. It is relatively straightforward to diagnose and successful treatment is usually possible, provided the clinician follows the recommended diagnostic processes, performs a thorough examination and conducts the appropriate tests. It is of short duration and provides a protective function, signalling treatable disease or enabling the avoidance of further injury.

Chronic (persistent) pain may be nociceptive (e.g. chronic arthritis), neuropathic (e.g. post herpetic neuralgia) or psychogenic in origin and hence can be difficult to diagnose accurately as there may not be any obvious signs or symptoms. It can also be difficult, if not impossible, to manage with analgesics alone, and other more appropriate management (including co-analgesics and psychological interventions) is required. It is often far more difficult to resolve than acute pain.