What is pain sensitization?
Pain is a sensation of hurt resulting from the activation of pain pathways by harmful stimuli to lead to tissue damage. Detection of the stimuli is a protective process to help the body prevent injury or to avoid further contact with the stimuli. However in many clinical conditions the pain is no longer protective, but causes harm. The pain in these situations arises spontaneously, can be elicited by normally innocuous stimuli, is exaggerated and prolonged in response to noxious stimuli and spreads beyond the site of injury. This is caused by pain sensitization. There are two types of sensitizations: peripheral sensitization is a reduction in threshold and amplification in the responsiveness of pain receptors. This occurs when the receptors are exposed to inflammatory mediators and damaged tissue. Central sensitization is an enhancement in the function of neurons and circuits in pain pathways. This is caused by increases in membrane excitability and synaptic efficacy as well as to reduced inhibition in central nervous system in response to activity, inflammation, and neural injury. As a result previous non harmful stimuli generate amplified signals. Central sensitization is responsible for many of the temporal, spatial, and threshold changes in pain sensibility in acute and chronic clinical pain settings and exemplifies the fundamental contribution of the central nervous system to the generation of pain hypersensitivity.