The cause of the majority of chronic pain remains elusive. Most of the diagnoses are descriptive, e.g. chronic low back pain, fibromyalgia, myofascial pain syndrome and chronic regional pain syndrome. Diagnostic tests are rarely helpful. X-rays and MRI findings of the lumbar spine correlate poorly with who goes on to develop chronic back pain, or even who currently has chronic back pain.
The "root cause" of chronic pain should be found somewhere within the organization of the nervous system: central and peripheral (somatic & autonomic).
I think it makes sense to take a holistic approach to find the mechanism of chronic pain. What if the problem was at the interplay of all the nervous system components?
Connection 1: Autonomic System directly activates Somatic System. The stress response, aka "fight or flight response”, is expressed through our voluntary musculature. The purpose of the stress response is to protect the organism from danger by activating the somatic nervous system. If the stress stimulus is severe or repetitive enough, due to an individual’s unique vulnerability, this activation can remain in the “on” position.
Connection 2: The brain has the “software” to contract or relax any of the 640+ voluntary muscles in the body, allowing us to be flexible and mobile. A maladaptive stress-response can interfere with this capacity.
Connection 3: The Sensory Nerves communicate to the Brain when danger is passed. Skeletal muscles have pressure-sensitive receptors (Golgi tendons and spindle cells) that are part of this feedback loop. Research shows that there is a pressure threshold where these receptors start transmitting pain signals back to the brain.
Connecting the Dots: Back Pain
Patient as a teenager fell off horse suffering a low back contusion. Patient has intermittent backache for several years. Discomfort typically goes away after 1-2 days of rest. Patient has acute episode of excruciating back pain after bending over to pick up a piece of paper. Pain subsides but doesn’t resolve completely. Patient becomes fearful of even minor activity since he has been told he has a “bad” back. Ten years later he develops degenerative disc disease and requires back surgery for disc rupture. He eventually ends up with lumbar spinal fusion, spinal cord stimulator, daily opioids and continued chronic back pain.
Explanation:
After the initial trauma (and stress response), some of back muscles stayed in a partial state of reflex, protective contraction. Partially contracted (tight and stiff) muscles, became the new baseline. Subsequent stressors would intermittently cause the muscles to contract further, causing them to go over the pain threshold and leading to bouts of pain. As time passed, more of the muscles became chronically tense.Picking up a piece of paper was able to trigger a large percentage of pressure-sensitive pain receptors, which had been just below the pain sensitivity threshold. The muscles were unable to relax beyond the threshold, putting pressure on muscle spindles and causing constant sensory pain signals to the brain.Minimal physical or emotional stressors were then able to create a stress response that was out of proportion to the stimulus, .i.e. there was no imminent danger.Chronic contracted intrinsic voluntary muscles created a vise around the disc, leading to disc herniation. These same muscles entered into a state anaerobic respiration leading to oxidative stress, free radicals and inflammation, which can contribute to spinal degeneration.Spinal fusion did not resolve the pain because the pain generator was the constant firing of pain signals from the intrinsic musculature, not the disc.
This explains the “root cause” of chronic pain: the autonomic stress response activates the somatic musculature to a level that sends pain signals to the brain.
The validity of this explanation could be tested if there was a way to reset the organization of the nervous system that breaks this dysfunctional pattern. By this I mean to get the brain to become aware of which voluntary muscles are in a state of reflex contraction. This awareness would allow the brain to use its inherent capacity to relax any voluntary muscle that is not in use.To paraphrase Robert Sapolsky- This is why zebras don't get chronic pain!
The next post will be about the person who discovered how to “reboot” the nervous system and empower patients to resolve the majority of chronic pain conditions.
Everything should be made as simple as possible, but not simpler.-Albert Einstein