So I was listening to a podcast the other day (http://www.mechanicalcareforum.com/podcast/49) and the question came up to me… Is a centralizing pain always discogenic?
…I agree that, most of the time, a pain that goes down the leg is from the disc.
Here are a few studies that supports this:
Centralizers are more likely to be discs. http://www.ncbi.nlm.nih.gov/pubmed/9160470
Tissue origin of pain: http://www.ncbi.nlm.nih.gov/pubmed/1826546
(e-mail me if you don’t have access to the full study)
But I don’t agree when someone says that a pain that centralizes is always a disc.
Let me explain. (Keep in mind it is theory… and it can still change… however, I think it’s the best model so far that can explain many weird things that we see in the clinic…)
Pain is created at the level of the brain… always. We all have a map of the body in the brain. It’s called the homunculus. No brain, no pain.
Which means that there is a representation of a lumbar disc in the brain.
When a disc is injured, it will send nociception (a danger message to the brain) and the brain decides whether it creates pain or not.
If the brain thinks it is worth creating the pain, then a neurotag of pain will fire. Pain will then emerge with the creation of that neurotag.
A neurotag is a combination of many neurons that fire together to create an experience. For example, when you bend forward, your premotor cortex fires, you might get a visual representation of you bending forward, or maybe a visual representation of one of your friend who suffered excruciating pain and went through surgery… or maybe it could be all the things that your therapist told you about your disc squeezing you nerve in the back and that you should completely avoid bending forward or your back will explode!? All those things will wire together to create the neurotag of pain. It creates pain.
Now, if a pain persists, this neurotag is created more easily. A great metaphor that I like is one from Adriaan Louw.
The angry neighbor analogy:
When your home alarm system goes off, your neighbors might notice it… but if it shuts down pretty quickly, nothing really happens…
Now imagine that your alarm system goes off every single day and stays open for many many hours. Or imagine that it doesn’t even close down! Well your neighbors are going to start to get irritated. It might wake them up more often… They might start to complain a little more!
The same thing happens when your pain has persisted for a while. Once one of the neurons (part of the neurotag) starts firing, the others will fire way easier than it should!
Therefore, if a patient comes with pain radiating down the leg with a hypersensitive central nervous system, I would say that there is a good chance that we should look beyond the disc model! Normal pressure on the disc can now create pain that mimics a “discogenic” type of pain. A pain that is able to centralize and peripheralize –> Even if the disc is completely healed.
Let me give you an example of a patient that completely changed the way I treat patients. It’s one of those patients that I will never forget.
That patient worked in a restaurant and got injured lifting heavy food from the floor (with a slight rotation of the lumbar spine). Pain started in the lumbar spine and radiated down the leg. She started worrying a lot and got very stressed because it was her business.
On the first day: already presenting with signs of centrally sensitized nervous system (I did not know back then) (to identify central sensitization: here). Pain radiates down the leg. Pain centralizes with repeated extensions, and peripheralizes with flexion. She had no improvements other that short relief of pain with the directional preference exercise.
One day, after reading a bit more on chronic pain and pain science, I tried a few things. I asked her to lie down, relax and think about different things.
- Think about bending forward: Ayyy! I can’t. It’s painful
- Think about bending forward… on vacations: it’s okay, not too bad
- Think about bending backwards repeatedly: Pain centralizes
- Think about being at the restaurant (where you got injured): Pain peripheralizes
INCREDIBLE!!! The most interesting patient I have ever had! The neurotag of pain, in this case, was created just by thinking (possibly the prefrontal cortex)!!
This patient taught me many things that I thought I should share with you:
- Mechanism of pain MATTERS. The pain was a predominantly central pain (even if there was nociception)
- I failed. I probably should have addressed the hypersensitive central nervous system sooner
- I got focused too much on “reducing” a derangement… whatever that means
- I kept a patient for too long. Should have discharge way earlier. I created dependence
- Very little is known in physiotherapy
I hope that this post helps you understand the wonders of neuroscience and pain.