ABSTRACT
There are several types of pain. Acute pain tends to be of sudden and relatively short duration. It serves a purpose in one sense, i.e. it alerts the individual that something is wrong and needs attention, or it protects the individual against further tissue injury. Chronic pain has a longer duration than acute, often lasting for weeks, months or even years. Some definitions put chronic pain as existing for longer than three months (Wood 2002) or longer than six months (Jacques 1994). Intractable pain is chronic pain unrelated to any detectable pathology. As such it is very difficult to treat and offers a major challenge to health-care professionals. Although there are some theories, there is no known cause of intractable pain.
