Low back pain 6- Central Sensitization

The mechanisms I described in the previous post  involve a process termed "central sensitization."  Let me explain.  The brain has a certain threshold at which it perceives pain.  This threshold is variable, not absolute.  In other words, there are moments when you have a lowered pain threshold and other moments when it is raised.  For example, if you are in the middle of an athletic event, your pain threshold is elevated because of a change in your neuroendocrine milieu.  A cut on your hand may not even be perceived until the game is over.  You don't actually feel "pain" even though the pain signals are being actively generated at the tissue.  While there are numerous places where this pain modulation occurs (spinal cord, brain stem, thalamus are a few...), it ultimately leads to a decrease in pain related activity in the brain.

"Central sensitization" is just the opposite.  When a pain loop has been running for some time, your brain gets really good at perceiving and running that loop. This can happen after an injury where a vicious cycle emerges to perpetuate the pain.

These authors describe one model where a painful stimulus may...

"...induce multiple inflammatory and neuropathic processes in the spinal cord dorsal horn, and trigger modification and plasticity of local neural circuits. As a result, ongoing noxious signals to the brain are amplified and prolonged, a phenomenon known as central sensitization."  Curr Pain Headache Rep. 2010 Jun;14(3):213-20.

Scientists are in agreement that this phenomenon occurs regularly.  The question that remains unanswered (although we can make educated guesses), is whether or not central sensitization is more likely to occur when there is pre-existing inflammation in the brain or the periphery.

Does an unhealthy physiology have a greater probability of allowing central sensitization to occur?  Does a person who eats well, has no inflammation, sleeps well, exercises regularly and manage his stress have a better environment that will resist the induction of these noxious pathways?

To be fair, we don't have a clear answer for this yet.  The science pretty much says, "maybe- but we can't preach that particular message with full confidence."  But when you consider the many health related "shades of gray" that brain can live in, when you consider our current understanding of pain physiology, when you appreciate the influence of food and nutrition on brain health and inflammation levels, it is not a giant leap of faith to believe that food is related to central sensitization.

If you know someone with chronic low back pain, I hope you are beginning to appreciate the absurdity of throwing multiple pain management modalities (ice, steroids, anti-inflammatory medications, exercises, physical therapy) at the individual without making fundamental changes to his diet.

Low back pain 5- Chemistry

Common mechanical causes of low back pain include disc herniations. Most clinicians acknowledge that if a tissue is damaged, there is a reasonable probability that it will produce pain.  In the 'old days', we used to believe that a disc herniation would pinch a nerve and lead to pain.  But as we realized that true nerve impingement (although it does occur) was less common than previously believed, the low back community began to look outward.

When there is tissue damage, lots of noxious chemicals are released. These chemicals are generally used to communicate with different components of your body that are responsible for healing and repair.  But it is becoming clear that these chemicals (broadly termed 'cytokines'), can be problematic if they persist.

This paper describes the production of inflammatory cytokines by damaged tissues. As they activate immune cells and the brain, the brain responds by promoting further release of these inflammatory triggers.  These authors describe the way that these signals cross the blood brain barrier and influence our perception of pain through a "cascade of altered neural activity."  This can promote the efficiency of the "pain pathways" to the brain and lead to persistent pain.

So far, so good.  But another question remains; is there anything else that leads to the production of these inflammatory cytokines?  In other words, can another event, apart from tissue damage at the low back, produce these nasty chemicals.  If so, then this would have the potential to make relatively minor tissue damage... a REALLY BIG DEAL.  The answer is a resounding yes.  Before we detail some of these components, picture this.

Have you ever caught a friend at just the wrong moment? Perhaps you made an innocent comment, "I like your other shoes more than the ones you're wearing."  And all of a sudden, your friend explodes!  It may have been a minor statement, but if she just got fired from her job, broke up with her boyfriend, had her credit cards stolen and her car is making funny noises, then your minor statement was the "straw that broke the camel's back" in an already traumatic day. 

If your brain is already compromised by a poor diet and lifestyle, then even a minor stimulus will lead to a major symptomatic eruption.  Remember, the brain not only maintains normal body mechanics, but also perceives pain.  Alteration in its function can heighten sensitivity and generate vicious cycles of pain.

Low back pain 4- Brain

We have further evidence that there are central neurological changes in individuals with chronic low back pain.  In this study, researchers found that in people with chronic low back pain, there was a decrease in gray matter in both the thalamus and prefrontal cortex.  The authors go on and state, 

"We hypothesize that atrophy of the brain circuitry involved in pain perception may dictate the properties of the pain state, such that as atrophy of elements of the circuitry progresses, the pain condition becomes more irreversible and less responsive to therapy."

In other words, the longer you have pain, the more that pain will establish itself as a regular part of your life by "rewiring" your brain.  At the very least, research like this suggests that in order to ameliorate low back pain, we must not only correct your peripheral structures (muscles, joints), but also address the brain.

Other experts agree with this idea.

"There is increasing evidence that chronic pain problems are characterised by alterations in brain structure and function. Chronic back pain is no exception. There is a growing sentiment, with accompanying theory, that these brain changes contribute to chronic back pain..." Man Ther. 2010 Jul 23. [Epub ahead of print]

Where does this leave us?  It suggests that everything we know about maintaining the health of your brain applies (to varying degrees) to chronic low back pain.  Brain research has exploded in the past 2 decades and we now recognize a variety of mechanisms to compromise the brain; inadequate nutrition, oxidative stress, stress hormones, lack of sleep, environmental triggers, gluten (to those who are sensitive), lack of exercise and so much more!  

There is truth to the thought that low back exercises will aid in brain function.  However, if those exercises are performed and the brain is then swamped with a Happy Meal (and the saturated fat, blood sugar surge, oxidative components, noxious chemicals, trans fats etc.) as you drive home from your physical therapy session, you are working against yourself.   Your are trying to re-wire the brain with the exercises, and then proceeding to assault it with your diet.  Food and low back pain are related.

In the next post, we will address other metabolic perspectives on low back pain. 

Low back pain 3- Respiraton

The diaphragm plays an important role in maintaining core stability.  It serves as the "top" of the core and its activation is timed to the activation of the abdominal muscles.  We know that in many cases, individuals with low back pain have altered respiratory patterns.  Spine. 2010 May 1;35(10):1088-94. 

In fact, some people that reach a plateau in their 'typical' treatment of low back pain respond quite well to breathing exercises.  Also, other researchers have discovered that in some individuals, problems with the diaphragm (and the subsequent low back pain), are coupled to failure to activate muscles of the pelvic floor.

We now have a picture of a person with low back pain and poor respiratory patterns (primarily chest breathing rather than using abdominal breathing techniques).  This person also fails to activate muscles of the pelvic floor.  We don't think of these muscles often unless we have a problem with urination (these muscles are trained during 'potty training') but they are also activated unconsciously as we stabilize the low back. 

The overriding question is; why do these muscles fail?  To answer that, we have to know what turns them on.  These muscles are activated by unconscious pathways from the brain and brainstem.  In other words, the nervous system turns on these muscles.  "Big deal" you could ask.  All muscles are activated by the nervous system.  The point that I want to make here is that it is generally recognized by the rehabilitation community that muscles do not fail.  Instead, the neural components that activate them will fail.  In other words, muscles don't tend to get truly "weak".  They tend to get "not activated" secondary to inhibition of those parts of the nervous system. 

As we dig deeper, we learn that the lower brainstem makes you breathe.  The lower brainstem is commanded by higher parts of the brain including the vestibular system. 

In other words a poor brain causes poor breathing which causes low back pain.  This is the missing "neuro" part that I wrote about in the previous post.  To be clear, I am not talking about a brain with true degeneration as in Parkinson disease.  I am talking about a brain that works at less efficiency or has a compromised level of integrity.

Low back pain 2

When you view low back pain, you can think of it from 2 perspectives.

1.  Biomechanical causes

2.  Metabolic causes

Most research has focused on the biomechanical causes of low back pain.  Truthfully, you could spend your entire life studying clinical biomechanics as it is a complex topic.  For example, in the 1980's, we thought you just needed to get some bed rest.  In the 1990's we realized that abdominal muscles were important in the stability of the back.  In the late 90's, gluteal muscles and legs were understood as important.  In the 2000's, there was an explosion of research on muscles with fancy names like; multifidus & transverse abdominis. And only fairly recently did many practitioners start appreciating the respiratory diaphragm and muscles of the pelvic floor.

As there are many practitioners who are skilled in this approach, I won't regurgitate this body of knowledge in this blog.  For more information, check out this blog by biomechanics expert, Will Stewart.  Will does a great job highlighting the importance of assessing all components of the kinetic chain from a variety of "real life" positions.  He also emphasizes a "real life" approach to rehab and exercise.  Great stuff and hours of mind-boggling reading.

I will mention that as we've learned more about the biomechanics of the spine, we've really come to appreciate the role of the nervous system.  While the term "musculoskeletal" has been around for decades, the term "neuromusculoskeletal" has been in use for the past 10-15 years as we've come to appreciate the role of the brain.

However, for most of those past 10-15 years, the "neuro" part has not been well described.  In the next post, I'll start there with the overall goal of bringing us into the metabolic arena.  I want to show you that to have a good biomechanical system, you must have a good "neuro"  system.  And to have a good "neuro" system, you must have a good endocrine and immune system.  And to have a good endocrine and immune system, you must eat well, manage your stress, sleep well and exercise... all the things that make you healthy.

Low back pain 1

Most of the entries I post in this blog have to do with metabolic issues (diabetes, obesity, inflammation etc.).  One of the underlying themes you may have gleaned by now is the integration of body systems.  Just when we think some component of our body works in isolation, science will demonstrate an intimate connection with other components of our physiology.  For example, in the series on heart disease, we saw how things like the gut, hormones, nutritional intake, and immune system influence the health of the heart.  For the next series, I want to tackle something just as prevalent; low back pain.

When you think of low back exercises, you may think of abdominal work.  If you find a more thoughtful therapist, he may recommend exercising the gluteal muscles (variety of squats or lunges) and stretching hamstrings.  An even more highly skilled therapist will integrate respiratory exercises and activation of muscles of the pelvic floor. Perhaps your therapist also examines the broader "kinetic chain" and examines your foot, ankle, knees and hips.  We often mistake this as a very sophisticated approach toward low back pain. I will admit that this is light years ahead of where low back rehab was just a decade ago, but we still have a long way to go.  

This paper changed my life forever.  In summary; 83% of patients who had chronic low back pain were found to have low levels of vitamin D.  They were treated with vitamin D and 95% of those treated had significant improvement in their symptoms!  The authors concluded, 

"Vitamin D deficiency is a major contributor to chronic low back pain in areas where vitamin D deficiency is endemic. Screening for vitamin D deficiency and treatment with supplements should be mandatory in this setting."

This paper was published in 2003 when I was in the middle of my residency.  In those years, I spent the vast majority of my clinical time performing physical rehabilitation on patients with musculoskeletal pain.  It irked me that the hours of physical exercise that my patients were performing may have been undermined by low vitamin D.  As more research uncovered the roles of vitamin D, it became clear that even something low back pain, more than likely, involved a intimate integration of physiological systems.

We'll take a closer look in the coming weeks.