Persistent nociception (perception of damage) or inflammation - the first is an uncommon cause of chronic pain, and inflammation, (recognized by redness, increased local temperature, swelling and inflammation) is usually self-limiting, unless there is abnormal immunologic response (in autoimmune disorders such as rheumatoid arthritis or lupus).
Abnormal function in the nervous system - neurogenic or neuropathic pain can arise from the Central Nervous System or Peripheral Nervous System.
Neuropathic pain can be due to direct nerve compression (e.g by a prolapsed disc); spontaneous nerve firing along a previously damaged nerve; deafferentation pain due to hypersensitivity of higher structures above the level of nerve damage (e.g. phantom limb pain) or sympathetically-mediated pain due to autonomic nerves being affected.
Neuropathic pain has the following characteristics:
- Pain is worse at night
- Pain in a numb area
- Pain produced by non-painful stimuli such as light touch
- Pain responds poorly to standard medication
There may be bizarre sensations such as water running down the leg
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