New Understandings of the Differences between Chronic and Acute Pain

David Shulkin, M.D., Override Cofounder

Much of the world continues to think of acute and chronic pain as only different with respect to only how long they last. Many people simply think of chronic pain as a direct continuation of chronic pain. After all, chronic pain is still defined, in its simplest definition, as pain that lasts longer than three months. But this doesn’t adequately explain why, on the one hand, acute pain responds better to medications and interventions and dissolves quite quickly, and on the other hand, chronic pain often seems unresponsive to treatment and can totally take over the lives of its victims.

Imaging of the brain reveals a fuller picture. fMRI scans clearly show the distinct footprint that chronic pain implants on the brain – one that is not mimicked by its acute counterpart. In other words, chronic and acute pain activate totally different parts of the brain. One study performed at Northwestern University showed that acute pain was present in areas of the brain involved in sensations, while chronic pain became more obvious in areas of the brain related to emotional regulation and memory. Other studies have shown that the anterior insula, which is responsible for assigning emotions, exhibits substantial change when a person’s condition shifts from the acute to chronic phase.

When we realize that the brain is processing chronic and acute pain differently, and that the consequences of chronic and acute pain for the brain are different, it seems like common sense to treat the two types of pain differently. It seems like it should be obvious that the same type of treatments and interventions that work for acute lower back pain, for example, are not going to work on the patient with 7 years of chronic lower back pain. Yet the majority of the medical community fails to distinguish between the two types of pain or leverage diverging treatment strategies.

The true nature of chronic pain still perplexes the majority of the medical and nonmedical communities as well. Many imagine that one simply gets used to living in chronic pain after doing it for so long – as though the sting would be less harsh. In reality, though, people with chronic pain become more and more sensitized to pain as their brains get used to experiencing pain and get better and better at perpetuating the pain cycle. This is called a central sensitizationi.e., a sensitization of the central nervous system. It can lead to the original pain spreading to a bigger area, spreading to other body parts, and becoming more sensitive to minor stimuli like having a heightened reaction to stubbing a toe.

Yet the problem is that our brains don’t have a good way of differentiating between acute pain (triggered by injury or tissue damage) and chronic pain (persisting through learned neural pathways). Acute pain serves a wonderful purpose of preventing us from further harm by letting us know that we are in danger. Chronic pain, conversely, is an error message – making us incorrectly think that we are in danger so that we avoid certain activities. Humans absolutely have to learn from acute pain to survive; it’s how we know not to leave our hand on a burning stove. Humans try to learn from chronic pain to avoid further pain; yet we misunderstand its message to us and often respond as though we were experiencing acute pain.

For patients, getting a better understanding of the differences between acute and chronic pain is one of the first steps to recovery. For providers, understanding this distinction is key to prescribing the right treatments to pain patients. Without knowing what we are treating and why, it’s difficult to find the path forward.

Posted on 
October 5, 2022

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