The Nervous System and Chronic Pain

Sometimes, pain can persist even after the original injury or disease that caused it has healed.

There are several different factors that can cause this.  The one that’s played the largest role in my own life involves the concept of neuroplasticity— the idea that the nervous system can change over time, and that in chronic pain sufferers, it can actually become more sensitive to pain.

In this post I’ll be sharing what I’ve learned about neuroplasticity, as well as some of the other potential causes for chronic, persistent 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 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.

Neil 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.

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 Factors in 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 (read this and this).  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

Numerous studies have demonstrated a relationship between depression and chronic pain.  I’m sure I will surprise no one when I say that chronic pain patients have been shown to suffer from depression at higher rates than the general population.

On the flip side, depression has been shown to cause physical symptoms such as back pain or headache.

What came first– the pain or the depression?– can seem like somewhat of a chicken vs. the egg question.  If you suspect depression might be playing a role in your pain, I would definitely seek professional help and investigate further.

However, I personally had the opposite experience, where I came to feel that many of the doctors I saw were too quick to attribute my pain to depression, even though I insisted repeatedly, and with absolute certainty, that I wasn’t depressed.  If you are being treated by someone who gives you the impression that they think your pain is being caused entirely by depression, and you disagree, I would definitely 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 does mean that depression and chronic pain are likely to share similar physical pathways in the brain, however.  Studies have demonstrated 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.