In this lecture, I would like to explain the difference between acute pain and chronic pain. There is very significant difference between acute and chronic pain. Acute pain usually arises from noxious stimuli which include pinch, heat or electric shock of significant intensity. In clinical practice, noxious stimuli include mechanical damage and chemical factors due to inflammation.
The clinical symptoms and signs of acute pain are similar to those seen in anxiety state: increased cardiac rate, increased blood pressure, pupillary dilatation, palmar sweating, hyperventilation, hypermotility and escape behaviour. Acute pain promote survival and restitution, thus serves useful biologic function to the body.
When pain persists, physical discomfort is alter ed by psychological factors and it becomes chronic pain. Chronic pain, by definition, persists for a long time (usually more than 6months). There may or may not be an identifiable underlying disease process or healing may have occurred, but pain persists.
The clinical symptoms and signs of chronic pain states are similar to those seen in depression states: sleep disturbance, irritability, appetite disturbance, constipation, psychomoter retardation, social withdrawal and abnormal illness behaviour. It is usually destructive physically, psychologically and socially. It serves no useful biologic function to the body.
Chronic pain can be divided into nociceptive related to tissue injury and non-nocicep tive which include deafferentation and psychogenic pain.
Nociceptive pain is the most common type in c ancer and chronic illness. However, chronic cancer pain has many of the characteristics of both chronic and acute pain. The pain represent continuous application of a noxious stimulus and continual renewal of acute pain. Yet, because of chronic distress and anxiety, it has many psychological components of chronic pain.
Deafferentation pain is due to nervous system injury that interrupts the neural transmission of sensory impulse. The most common type of deafferentation pain are brachial plexus avulsive pain, post-herpetic neulargia, phantom limb pain and thalamic pain, syndrome.
Psychogenic pain may take the form of somatic pain without any organic pathology or pathophysiological mechanism to account for the pain.
Chronic pain is different from acute pain not on ly from the view point of psychological aspect but from that of mechanisms. In this respect, I will explain the difference between acute pain and deafferentation pain.

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