There are several kinds of pain. The pain from injury to the muscles, tendons and ligaments or from a broken bone is different that the pain from injured nervous tissues (such as the nerves in our arms and legs, the spinal cord or the brain).This last kind of pain is called neuropathic pain. Neuropathic pain occurs in some but not all people with injury or dysfunction of the peripheral or central nervous system. Neuropathic pain is estimated to affect up to 7-8% of the general population. This means that close to 2.5 million Canadians (one million in Ontario alone) are affected by this type of pain.
In case of injury to nervous tissue, all parts of the nervous system may undergo changes within milliseconds, which may last indefinitely. Specifically, when peripheral nerves get injured, they may fire abnormally generating “ectopic impulses” at the site of injury and becoming supersensitive to multiple neurochemicals. This phenomenon is called “peripheral nociceptor sensitization”. Similarly the spinal cord and the brain undergo changes after damage to the peripheral nerves or after spinal cord injury or stroke (“central sensitization”). Some of these abnormalities include pain seemingly coming from body areas larger than the original injury site or generated by stimuli that are normally painless, for example pain on mere touch. Understanding of neuropathic pain has increased dramatically over the past few years with the invention of neuroimaging, a method of visualizing brain activity in people who are awake. It is used exclusively for research and has shown many changes in brain activation patterns, even when our everyday tests fail to show abnormalities.