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The science of chronic pain


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The words 'The science of chronic pain' are in the centre of the image in black text against a white text box. Behind this is a light green background, which is scattered with small images all fitting the green and purple colour scheme; a biological cell, light bulb, book that says 'science' on it, and demo tool used to show chemical structures. At the top, is a purple outline of a seated person with their knees to their chest and lightning emanating from a cloud above them.

In the first of our series on chronic pain, we looked at the definition of chronic pain (recurrent or lingering pain lasting longer than 3-6 months) and discussed some general information about it but we didn’t get into the science.

I’ll preface this by saying I am not a doctor, so I recommend doing your own research and trying to see a qualified pain specialist about your unique needs and specific experiences, if this is accessible to you. I’ve learned a lot about chronic pain through the NHS program I was lucky enough to access a few years ago.


Let’s start with some anatomy… There is no ‘pain centre’ of the body. Pain is experienced via a complex combination of our nerves, immune cells and chemicals. These elements interact, combining with the additional inputs of our sensory experiences, memories, and emotions to create systems of pain, called neuro-signatures (or neuro-tags). There are three categories of chronic pain: nociceptive, neuropathic, and nociplastic. All three have different mechanisms and can feel very different.


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The words 'Nociceptive - tissue damage, Neuropathic - nerves, Nociplastic - 'sensitisation' of the nervous and immune system' are in the centre of the image in black text against a white text box. Behind this is a light green background, which is scattered with small images all fitting the green and purple colour scheme; a biological cell, a brain, a knee or elbow joint and nerve cell.

While chronic pain is often a symptom of an injury or other illness, it is now widely considered its own disease. The majority of chronic pain is caused by nociceptive tissue damage. Nociceptive pain can be further categorized as either somatic or visceral, with somatic pain relating to the skin, muscles and soft tissues, and visceral pain relating to the internal organs.


Some examples of nociceptive pain include bruises, burns, fractures, postoperative pain, arthritis, tendinopathy, dislocation and subluxation (partial dislocation). It is often described as sharp, aching, throbbing, or a deep bone ache, and can be made worse with movement. Nociceptive tissue damage tends to be localised, and thus the pain experienced feels localised and source is easier to identify.


Then there’s neuropathic pain, which is nerve pain and is generally caused by things like diabetic neuropathy, nerve root compression, complex regional pain syndrome (CRPS), brachial plexopathy, shingles and occipital neuralgia. People with MS often experience this kind of pain and it is often described as “shooting” or “electric”.


Strangely, many people experience a third category of pain which involves nothing testably wrong with their bodily tissues (certainly not beyond 3-6 months). There is no clear anatomical issue to resolve though surgery or other interventions. This is nociplastic pain, and the mechanisms behind it are not yet fully understood by scientists. A person with nociplastic pain’s nervous and immune systems have become ‘sensitised’ through the prolonged experience of being in pain and now the body can’t forget that pain. Nociplastic pain tends to be more generalised and can be especially challenging to manage.


Around 20% of people who have routine knee surgery still experience pain in the knee after their surgery is completed and tissues have had ample healing time. So, a person can start off with nociceptive knee pain due to osteoarthritis, then following surgery and the passing of typical healing time, their pain becomes nociplastic in nature. The reasons for this are not fully understood but it could be inferred that during the time waiting for surgery, the body's nervous and immune systems become hypersensitised to the pain.


All three types of pain are real and can be highly disabling. All three types can be experienced simultaneously (like ya girl here), or a person can have just one or two. A person’s perception of pain is not only affected by the biology, psychology and social experiences of the individual, but that pain has a very direct impact on the person’s biology, psychology and social experiences. It’s a two-way street, a bi-directional relationship.



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The words 'Chronic pain involves the dynamic interplay of a person's biological, psychological and social realities.' are in the centre of the image in black text against a white text box. Behind this is a light green background, which is scattered with small images all fitting the green and purple colour scheme; A triangle outline (representing Maslow's Hierarchy of Needs), an empty plate with a fork resting on it, a house, 3 people with their arms around each others shoulders, and a brain.

In the 1970s, improved understanding of this multi-factorial nature of chronic pain led to a more holistic approach to managing it, the Biopsychosocial Model. To help patients with chronic pain requires a multidisciplinary approach, that takes into account the whole reality of the person, the dynamic interplay of their biological, psychological, and social realities.

Chronic pain is impacted by factors such as income, social network, housing, access to health and social care, sleep, perceptions, memories, traumas, and coping mechanisms. So, it is no surprise there are some glaring inequalities when it comes to chronic pain (which we’ll cover in the next one).

Pain is such a valuable evolutionary asset, we are primed to give it our focus. We instinctively listen when our bodies are giving us danger signals. It can be challenging to manage chronic pain, but the Biopsychosocial Model can both help us find approaches to managing it as well as identify obstacles to its management.

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The words 'Pain is such a valuable evolutionary asset, we are primed to give it our focus.' are in the centre of the image in black text against a white text box. Behind this is a light green background, with purple lightning scattered around the text box in a circular shape.

Few of us will have the luxury of a life with no stress or trauma. But where they can be mitigated through policy and infrastructure, it makes sense to. Around 1 in 5 people in the UK were living below the poverty threshold in 2021-22, with over half being in households with at least one adult in work. The number of people in poverty will be much higher now, in 2023. Poverty and all that it entails exacerbate chronic pain for those already living with it, and manufacture new cases, as people struggle under hostile biological, psychological and socioeconomic conditions.


The body of scientific evidence is very clear on this; going without heating, food, housing, healthcare, sleep and other foundational needs is the most effective way of increasing chronic pain. Given the prevalence and economic burden of chronic pain, if policy makers really want to “get disabled people into work” in a sustainable way, they need to prioritise creating an equitable society, with focus on minimising stress for all.


If you live with chronic pain, your body works harder than most to get through the days. If you are able, do what you know will soothe your individual pain, even just a little. Maybe take that rest you need, smell some good smells, feel your favourite textures on your skin, enjoy some gentle movement, breathing exercises, time in nature, pet hugs, music, or comedy. You deserve to have your pain dialed down through positive sensory inputs.


Arianne Brown


Sources:

‘Chronic pain: an update on burden, best practices, and new advances’ Lancet article 2021

'What is pain?', British Pain Society article

What is a Pain Neurotag? The Integrative Pain Science Institute

Nociplastic pain: towards an understanding of prevalent pain conditions. Lancet. 2021

What is nociceptive pain? Healthline article, 2018

'The Biopsychosocial Approach', Practical Pain Management, 2008

Development of a complex intervention for people with chronic pain after knee replacement: the STAR care pathway, 2018

Poverty in the UK: Statistics (6th April 2023)

UK Poverty 2023: The essential guide to understanding poverty in the UK, Joseph Rowntree Foundation (2023)







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