Pain is a hard concept to define - everyone has experienced it, but it is not easy to communicate. There are very many types of pain, but it may be useful to broadly divide them as follows:
- nociceptive pain: the activation of physiologically normal nerve fibres in response to noxious thermal, chemical or mechanical stimuli. It may be subdivided into:
- visceral pain, which is pain from the heart, gut, kidneys, etc. This type of pain evokes an inward looking concern in the patient in the sense that it is somehow perceived that the pain is warning of some risk to the sufferer.
- integumental pain, which is pain in the skeleton, muscles or bone. This sort of pain, although worrying for the patient is not associated with the same fear as the visceral pain, as if the patient has an innate understanding that this is not a life threatening experience.
- neuropathic pain: arising from abnormalities or damage to the nervous system in the absence of nociceptive stimulation. Examples include pain due to:
- mononeuropathies, e.g. post-traumatic neuralgia
- polyneuropathies, e.g. in diabetes
- deafferentation, e.g. post-stroke pain
- reflex sympathetic dystrophy
- psychological pain
There can be combinations of the three main classes.