Sometimes after trauma (even minor trauma) to human tissue, a chronic pain condition develops. Once called i>reflex sympathetic dystrophy (RSD), this syndrome is now referred to as complex regional pain syndrome (CRPS).
With CRPS, the pain generated is greater than expected for the degree of tissue trauma that has been sustained. The pain begins early on and spreads from a small, local area to a larger, regional distribution. Patients report a burning sensation that comes on suddenly for no apparent reason. It is intense. Usually, there are other symptoms such as sweating, hair growth, and changes in skin color and texture.
No one knows for sure what causes this to happen. Lab studies of blood and tissue samples appear normal. There is no apparent inflammation of the affected soft tissues (e.g., skin, muscles). There is some evidence that the cellular changes are occuring within the nerve fibers to the affected tissues. Most of what we’ve learned so far has come from animal studies.
It appears that there is an over reaction of the neurogenic inflammatory process with too much release of substance-P. Substance P is a neuropeptide that acts as a messenger of information in the nervous system.
Substance P is released from the ends of specific sensory nerves. It seems to be able to increase the excitability of pain responsive neurons. That may answer some of the questions about why people develop so much pain, but it doesn’t answer the question of why those particular people have this pain response after an injury.
More study is needed to narrow down causative or predictive factors. Determining why some people seem more susceptible than others may help us find a way to identify those folks early and stop this painful process from ever getting started.