Chronic Pain: a Mental Model
Monday, May 06, 2013
Posted by: Joy Ingram
by Malcolm Butler, MD, Medical Director, Columbia Valley Community Health Services
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Chronic pain is difficult for many health care providers to understand. Pain out of proportion to physical findings triggers concerns of malingering and secondary gain. Prescription drug abuse, misuse and diversion are daily problems in our practice. We all want to help our patients, and many of us reach for a medication to treat chronic pain even without sound evidence that it is a treatment of choice.
To care with compassion for this challenging population of patients, a caregiver must have a rational mental model of how such pain occurs, is sustained, and is best treated. The model I describe fits what I have seen in over 20 years of clinical practice, and I have never seen it refuted in the medical literature. Thus, while not empirically established it remains a useful tool as we confront a challenging problem.
Pain is an adaptive response to a threat to our physiologic integrity. The absence of pain can sometimes lead to rapid injury and loss of life or limb. We should NOT work to remove pain from our patients, but rather to interpret it and assist our patients so they learn to manage their pain during their daily lives. Coping with chronic pain has more to do with a balanced and healthy lifestyle than to do with external forces such as pharmaceuticals or medical interventions.
Acute pain is largely a result of “nociceptive” inputs related to tissue injury, stretch, compression or inflammatory elements. The overall impact of emotional state or secondary gain on acute pain is small, and “fitness” contributes minimally.
Chronic pain is pain that persists, frequently related to a chronic condition such as rheumatoid arthritis (RA), or degenerative joint disease (DJD). Frequently we can establish no physiologic basis for the persistent pain. Regardless of its source, the perception of chronic pain is influenced by a combination of tissue based nociception and emotional and social factors. It is clear that over time, “practicing” pain makes one better at feeling that pain; it makes one more sensitive to it.
All pain signals are processed through the amygdala, in the mid-brain, and evaluated in the forebrain. Emotional memories are stored in the amygdala and impact our interpretation of pain signals from the periphery. Social isolation, loneliness, or a history of emotional abuse makes chronic pain more difficult to tolerate, while a calm and balanced amygdala may help us better tolerate chronic pain.
We all know some patients with chronic pain who have discovered ways to manage and accept it. Others find such persistent pain intolerable and overwhelming. The difference between these two groups has more to do with their physical fitness, emotional fitness, and resilience than to the actual cause and nature of their pain.
Pain is broadcast from a source, and perceived by a brain. In acute pain, a relatively naked brain receives a barrage of nociceptive input, and responds appropriately to preserve the organism. The pain resolves in short order, and the brain returns to its native state of quiet vigilance.
In chronic pain the receiving brain is not optimally tuned, misrepresenting external and internal inputs as “pain.” A fit body and a resilient emotionally healthy mind can handle repetitive pain inputs and respond appropriately. An unfit body, a life out of balance, a mind that is burdened by emotional traumas and excessive exposure to chemical pleasures, cannot handle repetitive pain inputs, or misinterprets them toward its other secondary needs.
The critical mission for the brain is to protect the organism: How much attention should be given to an issue? Chronic pain syndrome is a problem of a brain that assigns too much salience to certain pain signals. Our job is to retune that brain so that it can appropriately interpret the pain signals reaching it, increasing resilience so the organism can tolerate repeated pain experiences in an adaptive way.
The “pain-brain” is very much like the CIA: it gathers information about what is going on in the outside world. Most of what the CIA gathers is just the background noise of routine daily living. The “pain-brain” must attend to all of the external stimuli flowing through the nervous system and pick up on important stimuli while ignoring all of the background noise. It must assign “salience” to each and every stimulus. The nature of the pain stimuli flowing through the organism is less important than the adequacy or proficiency of the pain-brain to interpret the pain stimuli. A small stimulus, if misinterpreted as very important, can be unbearable; repeated severe pain can be borne with forbearance, however, when understood in context.
Some pain-brains do an excellent job of this task; others do not. Perhaps they are too burdened with years of emotional pain and cannot feel safe, or perhaps they were exposed to certain pleasure chemicals and are miswired, or perhaps they are tired and sad and lonely and just not up to the task. The important point is that it is not the stimulus that we must work to modify, but rather the proficiency of the interpreting pain-brain.
In chronic pain the inputs are assigned unreasonable or inappropriate salience, and no matter how the organism reacts the pain doesn’t abate. Even small tissue nociception might be perceived as intolerable. How the inputs are interpreted (or misinterpreted) is actually more important in chronic pain.
In my training I learned how opioids and NSAIDs muted the nociceptive inputs, how anti-epileptics and tricyclics could slow the processing of the inputs, that there was a “gate” in the spine that would allow only one signal to pass at a time. I learned that fitness could help reduce pain and avoid future injury. What I was never taught was that different brains perceive pain differently, that your pain-brain is the product of your genetics and your entire life experience. I assumed that just as we (almost) all perceive the color red in the same way (as the color red), we all perceive pain in the same way. In fact, we don’t all perceive pain in the same way. Our perception of pain is nothing like our perception of color. Our perception of pain is much closer to our perception of beauty. Just as we might regard a painting or piece of music and evaluate its beauty, our brains must regard a pain input and evaluate its salience.
Moreover, in my training I never learned how to increase emotional fitness or resilience. I certainly was never taught that teaching coping skills would be as important as prescribing pharmaceuticals.
So with this new mental model of chronic pain, we can better understand why the effectiveness of any pharmaceutical in chronic pain relates largely to its central effects. We can also better understand why comorbid behavioral disease or addiction complicates chronic pain.
That anxiety and depression are ubiquitous in chronic pain is apparent in that most if not all chronic pain patients benefit from antidepressants, and that a very large subset of opioid users are also dependent on benzodiazepines. A calm and balanced pain brain is more “fit” and resilient and more capable of tolerating chronic pain. A chemically dependent brain stops learning and adapting, is intermittently irritable and distracted, and has discovered that the misinterpretation of a pain’s salience will often result in a chemical reward. That is, their chronic pain will be treated with opioids. Similarly, with this new model of chronic pain we can better understand the perils of opioids, and we can better envision the optimized care team for chronic pain.
Coming together to share our mental models of pain and our discoveries related to the efficacy or inefficacy of opioid prescribing, healthcare professionals can forge a path to dramatic improvements in the safety and effectiveness of the chronic pain treatment that will always be part of their lives as providers. A case in point was the National Summit on Opioid Safety convened in Seattle last October by Group Health and Group Health Research Institute.
We have another such opportunity later this month when the clinical and administrative leaders of the community health centers of the northwest gather in Anchorage for an entire day of learning and sharing called “Chronic Pain After Opioids.” I look forward to participating in that exchange on May 18, 2013, a chance to share my mental model and learn from others so we can create a roadmap for a healthier future and a plan to get there.
 Nociception (synonym: nocioception or nociperception) is defined as the neural processes of encoding and processingnoxious stimuli. It is the afferent activity produced in the peripheral and central nervous systems by stimuli that have the potential to damage tissue.
 Rheumatoid arthritis (RA) is an autoimmune disease that results in a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks flexible (synovial) joints. It can be a disabling and painfulcondition, which can lead to substantial loss of functioning and mobility if not adequately treated.