The Nervous System and Chronic Pain

There are many theories behind what causes chronic pain.  The one that has played the largest role in my own life involves the concept of neuroplasticity– the idea that the brain can change over time, and that in chronic pain sufferers, the brain actually becomes more sensitive to pain.  In this post I will talk about what I have learned about neuroplasticity, as well as some of the other potential causes for chronic pain.

Neuroplasticity, or Practice Makes Perfect

They say practice makes perfect— in scientific terms, this is known as neuroplasticity, or the idea that the nervous system can be molded and changed by different experiences.  The more chances you give your nervous system to perform a task, the better it becomes at it.  In most cases this is a good thing—neuroplasticity allows you to learn how to walk, how to ride a bike, how to play the piano.  This ability of our nervous systems to learn new information and adapt to different life circumstances has been a fundamental part of our evolutionary history.

But sometimes this tendency of our nervous systems to become better at things with practice is a bad thing.  If you give your nervous system enough “practice” experiencing pain, it will become better and better at it.  The pathways between your nerves and your brain involved in sensing pain will become more and more developed.  It’s as though you’ve turned up the volume dial in your head, and now you hear everything, even the quiet parts, at an incredibly high volume.  For some people, even a tap on the shoulder or the feeling of clothing on their skin can be excruciating.

There are a few scientific terms to describe this phenomenon, but the one that seems to be the most widely used is central sensitization.  “Central” refers to the central nervous system (the brain and spinal cord) and “sensitization” means, well, the process of becoming more sensitive.

People who go through an extremely painful physical experience may find later that they suffer from central sensitization.  It could be a car accident, a severe injury, or even surgery.  Anything that is traumatic to the body can begin this snowball effect in which the constant pain signals traveling through your nervous system cause it to be more and more sensitive to them.  The exact reasons why it happens to one person versus another are not known.

I developed my chronic pain disorder a few months after my surgery for compartment syndrome in 2004.  It’s possible that the surgery itself triggered the changes in my nervous system– as one physical therapist explained it to me, being cut open is very traumatic for the body, whether or not you are awake to experience it. The other possibility is that it was triggered when I threw my back out a few months later.  That was the point at which the chronic pain began and never really left me.  I’ll never really know for sure which it was, because many people have told me that it can take some time for a chronic pain problem to manifest itself even after the precipitating event.  In all likelihood, it was a combination of the two things.

Pain Alarm System

Neil Pearson and other pain scientists describe pain as the body’s “alarm system.” This alarm system allows your body to communicate with you either that physical damage to your tissues has already occurred, or that physical damage might occur.  Pain is a protective mechanism; it alerts you when you need to take action, or to stop doing something that could damage your body.

In people with chronic pain, the pain alarm system has gone into overdrive, and it has begun to warn you about things that, in reality, do not really pose a danger to your body.  Of course, you have no way of knowing that– the changes to your nervous system occur completely outside of your conscious control, and all of the pain you feel is real.  Just because sometimes pain does not correspond to actual physical injury does not mean it feels any different to the brain.  All pain is 100% real, whether it stems from any sort of damage to your body, or from sensitization of the nervous system.  This is when you end up like me, going to the doctor’s office all the time only to be told they have no idea what’s wrong with you.

I find a lot of comfort in remembering that pain is an alarm system.  Our bodies developed the ability to experience pain not to torture us (though it definitely feels like it sometimes) but to help protect us.  Pain is what tells you to take your hand off of a hot burner, and not to walk on a broken leg.  It’s what tells you not to take that stretch so far that you tear any muscle fibers, and not to try to lift that heavy weight again.  Pearson likens an overactive pain alarm system to an overprotective friend: your friend is worried about you, and really wants you to stop doing whatever he or she thinks you’re doing that is so dangerous.  His advice on how to deal with this “overprotective friend” has helped me more than anything else on this chronic pain journey, and I’ll write more about my experience with that in a later post.

Myofascial Pain Syndrome

Here is where things get a bit complicated.  Although myofascial pain syndrome and central sensitization syndrome are technically not the same thing, I am not convinced it’s fair to think of them as completely separate disorders. I have symptoms of both, as I think most chronic pain sufferers do.

I generally defer to the Mayo Clinic website when I want a definitive answer on such matters.  According to them, “In myofascial pain syndrome, pressure on sensitive points in your muscles (trigger points) causes pain in seemingly unrelated parts of your body. This is called referred pain.”

A diagnosis of myofascial pain syndrome is generally based on whether or not the patient has these painful trigger points.  The Mayo Clinic says that this condition “…typically occurs after a muscle has been contracted repetitively. This can be caused by repetitive motions used in jobs or hobbies or by stress-related muscle tension.”

I don’t know about you, but to me that last part about muscle knots forming due to “stress-related muscle tension” starts to sound similar to what someone who has gone through central sensitization would experience.  At least, it does when you consider that one of the theories for the cause of trigger points is that that they form near a nerve that is constantly freaking out due to chronic pain.  The idea is that when you have pain signals flooding your nervous system day in and day out, your body reacts as though its been damaged.  Your muscles spasm up as a protective mechanism, to keep you from using the “damaged” part of your body until it heals.  This is why I find it hard to view myofascial pain syndrome as entirely separate from the idea of central sensitization.

Other Potential Causes of Chronic Pain:

Sleep Deprivation

Studies have shown that when you take generally healthy people and deprive them of sleep, they begin to exhibit the same symptoms reported by people with fibromyalgia.  This is not to say that sleep-deprivation has been found to trigger chronic pain all on its own, but its certainly interesting, especially for someone like me who has had life-long difficulty sleeping.  Personally, I think it’s very possible that my perpetual difficulties sleeping contributed to my developing a problem with chronic pain.

Depression

Some studies have shown that people with depression are more likely to experience chronic pain.  To me, this doesn’t mean that much because I’d expect that people with chronic pain are also more likely to be depressed.  I’m sure there is a real relationship between depression and chronic pain in some cases,  however, I believe doctors and physical therapists too often attribute a patient’s pain to depression and other mental health issues simply because they don’t know very much about pain science.  If you are being treated by someone who gives you the impression that they think your pain is being caused entirely by depression, I would probably look for a second opinion.

Anti-depressants have been shown to help with chronic pain, but that doesn’t necessarily mean the pain was caused by depression.  It could just mean that the anti-depressants create some effect in the brain that reduces the experience of pain.  Supporting my argument is the fact that much lower doses of anti-depressants have been found to be helpful for chronic pain than are normally needed for depression.

Maybe Your Doctors Have Missed Something

Yes: in my book, this counts as an official cause of chronic pain.  If your doctor doesn’t understand why you are in pain, he or she will probably tell you that you have an increased sensitivity to pain.  This is not always a safe assumption.  People don’t always undergo central sensitization after an injury (I certainly had my share of running injuries in high school, but up until I developed compartment syndrome, I always recovered from these and was eventually pain-free).

Doctors miss things all the time.  Perhaps you have scar tissue in your knee that’s getting in the way from an old injury or surgery.   Perhaps one of your legs is almost imperceptibly longer than the other and you need orthotics and a lift in one shoe.  Don’t let a diagnosis of chronic pain make you stop looking for other answers.  You may indeed have a problem with central sensitization, but you might find there are very real orthopedic interventions you can make to cut down on your level of pain.  At the very least, don’t give up looking for other answers before you have an X-ray or MRI of the afflicted part of your body.


6 thoughts on “The Nervous System and Chronic Pain

  1. Interesting, I hadn’t heard the term ‘central sensitisation’ before, but my mother has Reflex Sympathetic Dystrphy / Chronic Regional Pain Syndrome, which is kind of based on the same idea.
    Have you heard of the ‘gateway (or gate control) theory’ of chronic pain before? I’m trying to work out if it’s another term for central sensitisation or if they’re separate but related concepts.

    1. Yes I have heard of it—they are separate but related concepts. The gate control theory of pain is a theory that describes how the nervous system works in all people, healthy or unhealthy. Central sensitization, on the other hand, is something that happens to the nervous system in people with chronic pain. At the risk of oversimplifying things, I think it’s fair to say that in someone with central sensitization, the “gate” is no longer closing correctly. Therefore, more pain signals are getting through to the brain than would be in a healthy person.

      I did a little research to refresh my memory before answering your question, and I found this great video on Ronald Melzack, one of the two scientists who came up with the gate control theory. It does a really great job of explaining the idea of gate control: http://www.youtube.com/watch?v=KRFanGInvlc

      And wow… chronic regional pain syndrome. I’m so sorry to hear your mother has that… it has always sounded really difficult to me, and it takes a lot to scare me! I plan to write a little bit about that on this blog because, as you pointed out, it is related to other central sensitivity syndromes.

      Hope that helps!

      1. To my understanding, that is an extension of the gate control theory – that in chronic pain, the gate is stuck open, which explains why in some cases pain persists after the source of the pain has healed / been dealt with. I find all this stuff so interesting :) Thanks for the video link!

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