Understanding to take action
Whether it’s chronic pain from an injury or a pathology like fibromyalgia, chronic pain is a pervasive and stressful condition often leading to exhaustion. If you are living with chronic pain, you are the first to know how it affects your daily life. It’s hard to feel a sense of control in your life when it’s your pain that dictates what you do, and for how long and when, however you could change that. It all starts with understanding the underlying mechanisms of chronic pain to then act accordingly.
This first blog post of this series on chronic pain is addressed to people living with chronic pain, their caregiver or anyone curious to learn more about this subject.
The role and function of chronic pain
Pain is defined by the International Association for the Study of Pain (IASP) as “ An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.” Let’s take the time to break down this definition. Firstly, pain is both sensory and emotional, so it’s detected by our senses, but interpreted as an emotion by our brain, usually a negative one. This is central to understanding chronic pain. It all starts in our body’s tissues, where we find the receptors sensitive to pain, they are called nociceptors. When they are stimulated, those nociceptors send a signal through the spine to the brain. Once in the brain, this signal is identified as pain and an emotional reaction emerges from this stimulation. So, the expression that pain is all in our head is true! It’s in the brain that it is identified and classified as such.
Pain has always played an important role in the modulation of our systems, it’s essential to our survival. Pain enables us to avoid threats to our integrity. When we grow up, pain is one of the fastest ways to learn something, but without our knowledge, our body develops many ways to modulate pain. Way before we can even feel the pain, our nervous system has activated systems to modulate that pain signal. Those mechanisms can be classified in two principal functions; one to intensify the perception of pain, and the other one to diminish it. In other words, some mechanisms facilitate the flow of information to the brain and the other one slows it down. But those mechanisms can go off the rails, becoming dysfunctional, this is when chronic pain settles in.
To illustrate those changes, let’s imagine someone who falls and fractures their wrist. At the precise moment of the accident, the nociceptors detect the stimulus and a signal is transmitted to the spinal cord through the nerves. Along the way, the signal will fluctuate depending on the facilitating or inhibitory modulations happening. The perception of pain is affected by these mechanisms, but also affected by the context of the event, the person’s past experiences, and even their DNA. That’s why two people won’t experience the same pain for the same injury. It is therefore normal and even necessary, at the time of an injury, to feel pain, and this for a certain period of time, for the duration of the healing process. In order to avoid further injury to the injured wrist, the body sends pain signals to restrict movement. This is what is called acute pain, which usually lasts from a few hours to a few weeks, and ensures the maintenance of physical integrity.
What is chronic pain?
Let’s go back to our hurt wrist example, the lesion is caused by a fall that resulted in a fracture. In this case, many tissues have been injured, like tendons, ligaments and bones. The joint is probably inflamed and the skin has turned blue or purple. Those are the normal healing processes while we are in the acute pain phase. It’s when the pain persists past this healing period that we call it chronic. The physical injury is gone, but we still feel pain, why is that? It’s the nervous system that keeps on firing pain signals to the brain, even though there is no physical lesion. Although, it’s important to acknowledge that the pain is real, even in the absence of injury. That is why people are often puzzled when talking about chronic pain, no trace of a physical problem can be found, even when using imagery. Yet the pain is genuine…
In time, the mechanisms of pain modulation, those that facilitate or inhibit the transmission of pain signals to the brain, are impaired. On one hand, nerves that did not transmit pain signals in the past can become conduits and now start to do so. There are now more pathways transmitting pain. On the other hand, the nociceptors can expand their area of activation. If we use our wrist example, that means the zone where the person felt pain, the wrist, can now expand to the hand or the forearm. More nociceptors can be activated, and each of them can be activated more easily, as they become more sensitive. Meanwhile, the signals that usually inhibit the pain signal are diminished.
All those alterations amplify the pain signal being sent to the brain. Our nervous system is now hypersensitive to pain. So, our friend that got his wrist injured, an injury that is now healed, still feels pain even when he closes his fingers. His pain can now be qualified as chronic due to the absence of tissue damage.
It’s important to mention that all those aforementioned alterations don’t just appear at the same time. Someone can develop one of the alterations alone, and another person can have them all.
Possible interventions
When one lives with chronic pain, it is essential to establish a custom course of action. Especially because the pain signaling alterations are not the only factor to take under consideration when finding solutions. To plan an intervention, the medical history, the chronic pain’s comorbidities (depression, fatigue, etc.), the age of the person, all need to be taken into consideration. Those are all points to discuss with a health professional. Possible interventions can be pharmaceutical ones, but a lot of non-pharmaceutical options have proven to be more efficient in managing chronic pain. The next article of this series will address the advantages and disadvantages of the different interventions.
Written by : Mathilde Lessard
Reviewed by : Martine Lauzé
Translated by : Kassandra McCullough
References
Cohen, S. P., Vase, L., & Hooten, W. M. (2021). Chronic pain: an update on burden, best practices, and new advances. Lancet (London, England), 397(10289), 2082–2097. https://doi.org/10.1016/S0140-6736(21)00393-7
Fitzcharles, M.-A., Cohen, S. P., Clauw, D. J., Littlejohn, G., Usui, C., & Häuser, W. (2021). Nociplastic pain: towards an understanding of prevalent pain conditions. The Lancet, 397(10289), 2098–2110. doi:10.1016/s0140-6736(21)00392-5
Kirkpatrick, D. R., McEntire, D. M., Hambsch, Z. J., Kerfeld, M. J., Smith, T. A., Reisbig, M. D., Youngblood, C. F., & Agrawal, D. K. (2015). Therapeutic Basis of Clinical Pain Modulation. Clinical and translational science, 8(6), 848–856. https://doi.org/10.1111/cts.12282
Vader, K., Bostick, G. P., Carlesso, L. C., Hunter, J., Mesaroli, G., Perreault, K., Tousignant-Laflamme, Y., Tupper, S., Walton, D. M., Wideman, T. H., & Miller, J. (2021). La définition révisée de la douleur de l’IASP et les notes complémentaires : les considérations pour la profession de la physiothérapie. Physiotherapy Canada. Physiotherapie Canada, 73(2), 106–109. https://doi.org/10.3138/ptc-2020-0124-gef
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