Pain is an extremely complex issue. Complex regional pain syndrome (CRPS) is a prime example of the new understanding pain specialists are finding in the world of pain. Explaining these problems have taken years, but we are finding new information on what is happening when these conditions develop. We know now that there are peripheral issues at the site of injury, problems at the spinal cord and the equivalent of a short circuit in the brain when these conditions occur. Pain is maintained by feed-forward pain reception and feed-back sympathetic efferent loops. The brain stem, hypothalamus, limbic system and cortex all play roles.
Once an injury occurs, pain receptors in the periphery of the body, at the skin, bone and joint start sending signals to the brain. The sensory fibers first go to the periphery of the cord – the dorsal root ganglion where the sensory cell bodies are located. These cells then send signals to the cord in the dorsal horn and then to the brain. At this point, the cells in the DRG also are putting out several inflammatory chemicals IL-1, TNF, and IL-6 that promote inflammation in the periphery and increase the pain sensitivity of the spine and brain. Not only do the nerve cells become active, but glial cells, which we thought were just inert insulation, become active and produce more of these chemicals that promote inflammation. These chemicals then make the nerve cells more sensitive to pain reception and increase the number of signals going to the brain.
Pain and Brain
The brain is the master processing of all nerve and chemical signals in the body. The signals from the periphery for pain travel to the brainstem, then to the hypothalamus, thalamus, limbic system and cortex. The chemicals produced in the periphery also sensitize the brain also to pain signals. There are also an increased number of signals going to multiple areas of the brain, overwhelming certain areas and stimulating brain areas that are active for anxiety and depression in the cortex and limbic areas. Furthermore, the increase in signals also interacts with the motor inhibitory signals that are supposed to block pain signals. Thus in CRPS, there are multiple regions with increased activity, from the periphery to the spinal cord and into the brain.
The treatment of CRPS is now becoming more complex. The first obvious treatment is to try to eliminate the factors in the periphery that are stimulating the sensory signals. This means trying to correct even the small injuries that stimulate pain receptors, allow healing of the injury. During the treatment of the injury, interfering with the delivery of signals to the cord and brain is also important. This may be done with a variety of interventional techniques, physical therapy, medications, and psychological techniques. When the peripheral treatment of the injury is incomplete, then a full array of pain management techniques may need to be fully explored and treatment needs to be coordinated by a knowledgeable pain management specialist with expertise of medications and advanced interventional techniques including implantable options.
Thomas Cohn, MD
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