Central Sensitivity

We all have patients who express pain that doesn't seem to make much sense. Each may typically be classified as a fibromyalgia, myofascial or a postwhiplash patient who might have had an accident over a year ago. A period of time has passed in which typically the tissue involved should have healed. "Everything hurts," yet range of motion is well within normal limits, and physical findings are not conclusive. With every visit comes the complaint of the usual "right midscapular pain," but "yesterday it spread to the left shoulder, or right hip," or "it's spreading to the right buttock." Your re-examination doesn't really reveal anything particularly different. Your treatment may provide relief for a day or two, but the problem returns or sometimes the same treatment exacerbates the symptoms. Symptoms do not fall within neat anatomical or dermatomal boundaries.¹

Unfortunately, for reasons not completely understood, the sensitivity threshold level of the central nervous system (CNS) is set lower in many patients, and stimuli that would not ordinarily reach central neurons are penetrating the brain. The brain becomes sensitive not only to physical stimuli, but also to psychological stimuli. There is much evidence in the literature describing the neurological changes that create this sensitivity state.^2-4

The brain in the sensitivity state magnifies painful stimuli and eventually magnifies even associated nonpainful stimuli. While a noxious impulse may be normally magnified so our bodies will rest or avoid certain movements to allow healing, in the sensitivity state, a chronicity develops, and the magnification area of the pain persists despite attempted treatment options.

It is necessary to realize that this is not "all in the mind" in a mental sense. It's in the mind in a physical sense. Neurotransmitters and neuromodulators are involved. While patients are in the central sensitivity state, the stress and pain may eventually overtax the endocrine, immune and autonomic systems, creating many additional symptoms totally unrelated to their original complaint!

While it is important in the treatment of these patients to treat some of the peripheral noxious stimuli that remains with them, it is necessary to explain to patients about the chemical changes and over-magnification of pain that has occurred in their central nervous systems. They must be made to realize that they really have a physical condition that is represented chemically and magnified in their brains.

We have all heard about positive thinking; that things will get better if we direct our thoughts in the right direction. These "thoughts" are healing bullets that create chemical changes that will demagnify the brain's interpretation of the pain. These patients must realize that they do not have a terminal disease, and that they can work through the pain. As their brains realize that past movements that were painful are now tolerable, there will be changes in neuronal pathways and the magnification of the pain will be reduced. Meditation, yoga and relaxation techniques are all beneficial in helping to change the physical manifestation occurring in their central nervous systems. It really is "all in the head" but with a new interpretation of "head."

References

1. Butler DS. The Sensitive Nervous System. Adelaide, Australia, Noigroup Publications, 2000.
2. Noguchi K, Kawai Y, Fukuoka T, et al. Substance P produced by peripheral nerve injury in primary afferent sensory neurons and its effect on dorsal column nucleus neurons. J of Neuroscience 15, 1995.
3. Willis WD, Westlund KN. Neuroanatomy of the pain system and the pathways that modulate pain. J of Clinical Neurophysiology 14, 1997:2-31.
4. Doubell TP, Mannion R, Woolf CJ. The dorsal horn: state dependent sensory processing, plasticity and the generation of pain. In: Wall PD, Melzaack R. Textbook of Pain, 4th ed. Churchill Livingstone, Endinburgh, 1999.