There’s no question that pain is an unpleasant experience for everyone. The impact on the lives of those who suffer from chronic pain (lasting for more than three months) can be significant. It not only affects their relationships, jobs and finances, it can have a devastating effect on their overall outlook of life.
So why do some people keep hurting? The answer lies in the neurobiology of our central nervous system (CNS). The CNS is composed of our brain and spinal cord. The peripheral nerves are literally miles and miles of “telephone wire” that are there to tell our CNS what is going on in our body. The pain experience represents a CNS alarm system; a mechanism by which our CNS is alerted to a “threat” in our environment. For example, you step on a nail. Your nerves alert your CNS that something is wrong with your foot. Your CNS turns its attention to your foot; you take out the nail, go to the doctor, get your tetanus shot, and within a few days your foot is back to normal.
However, research shows that in 25% of all persons, the alarm system does not go back to “normal”. It resets itself in a sensitized manner. Chemically this means that pain impulses traveling down the nerves can travel more readily and more frequently. Thus, your CNS gets a lot of alarm messages and raises the overall threat level within itself. This results in the brain and spinal cord undergoing some chemical and physiological changes.
In the brain there exists something called the “sensory homunculus”. It is the sensory representation of our body that is mapped in the sensory cortex of our brain. Body parts are represented by the number of nerve endings they have. This means that the more sensory nerves a body part has, the bigger the representation is. The hand and lips, for example, are quite large. When this sensitization occurs, the sensory homunculus changes and the body part involved in the pain complaint enlarges.
The other thing that happens is that the edges of this body part in the sensory cortex (what separates it from other body parts) becomes smudged. That is, the brain can’t easily distinguish that body part from adjacent body parts which is why chronic pain seems to spread to other areas of the body. One other change to the sensory homunculus is that the brain stops being able to differentiate between the right and left sides of the body. As the sensory homunculus becomes more distorted the “threat” messages to the CNS become more and more frequent, resulting in more and more pain.
There is no specific imaging study or medical test that diagnoses this CNS sensitization. Rather, a well-trained clinician can tell from clues given in the history of the complaint from the patient, that this is going on. There are also some clinical tests to objectively measure it. For example, a sensitized CNS will not be able to differentiate between a two point stimulus and a one point stimulus. A pin wheel rolled on the affected area will feel a lot sharper than when rolled on an area not involved in the pain complaint. The skin can be affected and a simple skin rolling test is now painful and restricted. There are several other clinical tests that can be performed by a knowledgeable clinician to determine if the CNS is sensitized.
How do we treat it? The current medical paradigm is to try to “fix” the disc, the arthritis, the tendon, etc. However, most of the time this is not successful as those structures are really not what is producing the pain; it’s the faulty alarm system. In order to reduce chronic pain, the CNS has to be reprogrammed to get the alarm system back to normal once again. This is achieved by a comprehensive sensory integration and retraining program. The brain and CNS have to be retrained to sharpen up the map in the sensory cortex to get it back to normal. This is accomplished by a steady diet of sensory exercises that the clinician administers and prescribes for the patient to perform. Research has shown that once the sensory homunculus or map is back to normal, the alarm system settles down and the pain recedes.
One last component of successful treatment is retraining the motor system. The motor system depends on the sensory system in order to function properly. During the sensitized state, when the alarm system is elevated and the sensory map is abnormal, the motor system is not getting correct messages about which muscles to fire and when. Thus, there is a pattern of weakness and discoordination that emerges in the muscular system. Once the sensory system is retrained, the motor system has to be retrained as well to strengthen weak muscles and improve the timing and quality of muscular contractions. This all leads to the patient being able to do more and more activities with no pain and with less fatigue.
Unfortunately, not all medical professionals understand the nature of this condition and how to objectively test for it and comprehensively treat it. Be sure to ask whether your clinician is familiar with central sensitization and has been trained in the evaluation and management of this condition. For those suffering from chronic pain in the lower back, shoulder and neck (as well as those who suffer from chronic headaches) there is hope for a more pain-free state and a return to normal levels of human activity.
By Kathy Berglund