ABSTRACT
In this chapter the working definition of pain is that formulated by the International Association for the Study of Pain (Merskey & Bogduk, 1994), which states that pain is: (1) an unpleasant sensory and emotional experience associated with actual or potential tissue damage; or (2) described in terms of such damage. Pain is always subjective and it is always unpleasant, so that some abnormal sensory experiences that resemble pain but are not unpleasant fall outside this definition. Many patients report pain in the absence of tissue damage or any identifiable pathophysiology. This often happens for psychological reasons but there is no way to distinguish their experience from that due to tissue damage and their complaint should be accepted as pain. The following definitions are taken from the Classification of chronic pain, published by the International Association for the Study of Pain (Merskey & Bogduk, 1994), and they explain some of the terms used throughout this chapter:
• allodynia: pain due to a stimulus that does not normally provoke pain
• dysaesthesia: an unpleasant abnormal sensation, whether spontaneous or evoked
• hyperalgesia: an increased reponse to a stimulus that is normally painful
• hyperaesthesia: an increased sensitivity to stimulation • hyperpathia: a painful syndrome characterised by an
increased reaction to a stimulus, especially a repetitive stimulus, as well as an increased threshold
• paraesthesia: an abnormal sensation, whether abnormal or provoked.
