Acute pain follows a predictable, finite pattern and is generally short-lived, self-limiting, as well as easy to diagnose and treat. Pain that persists for longer than three months, and is not progressively better, is referred to as "chronic". It can be difficult to pinpoint the exact factors that cause chronic pain to persist over time (Lumley 2011).
Although there are many ways to organize different types of pain, one of the most popular and accepted schemes utilizes the following eight classifications to differentiate pain complaints (Smith 2005):
|Classification of Pain
||Mild, Moderate, or Severe|
||Acute or Chronic|
||Lower back, Abdomen, or Head|
||Nociceptive or Neuropathic|
||Muscular, Neurologic, or Skeletal|
||Central or Peripheral|
||Cancer or Non-cancer|
|Response to treatment
||Opioid-responsive or Opioid-resistant|
There are 2 major categories of pain; nociceptive and neuropathic (NINDS 2012):
Nociceptive pain guards the body against potential injury. It occurs as a result of the activation of peripheral pain receptors called nociceptors, which are activated by injurious stimuli. The stimuli is converted into an electrical signal, which is conveyed along nerve cells into the spinal cord or brain, where it is perceived as an unpleasant sensation (Cohen 2011).
Neuropathic pain occurs as a consequence of either injury or dysfunction in the nervous system. It produces a variety of unusual pain sensations that have been described as burning, crushing and "pins & needles." Unlike nociceptive pain, neuropathic pain often persists for prolonged periods of time, even after the original trauma and/or dysfunction is addressed (Costigan 2009). Since neuropathic pain is more complex than nociceptive pain, it is consequently more difficult to treat (Vorobeychik 2011).