Why do people seem to have different 'pain thresholds'? What makes a usual 'niggle' turn into a severe episode of pain? Or years of pain? What are the thoughts and research behind conditions such as Fibromyalgia?
These are some of the questions that come up a lot within the musculoskeletal treatment world. I've personally seen and treated a number of patients with chronic pain conditions and have always been interested in increasing my understanding of the potential mechanisms and neuroscience behind this subject.
Research has matched this curiosity, with a large push with the 'Pain Science' field in recent years, particularly from Dr Lorimer Mosely and Dr David Butler, who wrote the book 'Explain Pain'. Their research and thoughts emphasize the fact that teaching patients the science behind pain is key in all painful conditions, from an ankle sprain to neck osteoarthritis to Complex Regional Pain Syndrome or Fibromyalgia.
It is the emphasis on not just the Biomedical Model of pain e.g. just looking at joint/tissue changes that cause pain, but at the BioPsychoSocial Model of pain e.g. tissue changes linked with psychological factors (thoughts, attitudes, perceptions) and social context.
To explain pain, we must look into the Nervous System...
There are two main types of pain currently identified...
Neuropathic Pain...
Neuropathic pain is due to damage/disease of the nervous system itself e.g. Diabetic neuropathy, Multiple Sclerosis, Sciatica due to mechanical damage etc.
Nociceptive Pain...
Nociceptive pain is due to other tissue damage/inflammation... and our brain's perception of this.
Certain neurons (nociceptors) throughout our bodies respond to mechanical/thermal/chemical stimuli (which can potentially cause tissue damage/inflammation due to chemicals such as Histamine, Bradykinin and Prostaglandins). When activated these neurons send 'warning signals' to your spinal cord, which sometimes then sends signals to your brain too.
This phenomena, called Nociception, is happening all the time, but only sometimes results in actual pain. A lot of the time the spinal cord quickly protects you from pain by movement e.g. the withdrawal reflex when touching something hot/moving the foot when stepping on a rock (see my previous blog on 'How resilient are you?...' for more information on these reflexes).
If the warning signals reach your brain, the brain makes sense of the signals based not only on the current information arriving but also based on information already stored e.g. past experiences. If the brain feels there is true threat, it creates pain.
The Psycho-Social Elements of Pain...
So, we've looked at the Biological elements of pain (actual tissue damage/inflammation/nerve damage).
But the interesting thing that we're starting to understand more and more is that our brains can create pain without these mechanical/chemical/thermal stimuli (and therefore without actual tissue damage). Our brains can also increase (or indeed decrease) our sensations of pain from actual tissue damage.
Thoughts about what tissue damage (i.e potential threat to survival) may be happening and other stimuli such as being around certain people, or indeed feeling lonely, being in certain places, seeing a certain object or even hearing something can trigger or exacerbate pain. Think about some people's reaction to injections for example- usual tissue damage is minimal, yet some people catastrophize so much at the thought alone of a needle that they end up exacerbating their stress and pain response! The same goes for other phobias and with what we call 'Fear Avoidance Behavior', creating limitations of daily movements and activities due to fear of pain. These are all psychological and social factors that can add to our pain experience.
Basically, your spinal cord and brain (central nervous system) can learn to generate unnecessary warning signals. This can be due to, or lead to, an over-active/hyper-responsive nervous system.
Central Sensitization...
With repetitive stressors (physical/psychological/chemical) e.g. repetitive nociceptive stimuli, repetitive negative thought patterns such as catastrophizing, or repetitive chemical stressors such as poor nutrition/gut microbiome issues triggering generalized inflammation, our nervous systems can sometimes become extra sensitive (related to the release of chemicals such as Nitrous Oxide).
'Neurons that fire together wire together' so when repetition happens our brains can adapt and learn these patterns (think of Pavlov's dogs and the conditioning that was shown to happen in this experiment with certain stimuli).
This may lead to a decreased pain threshold, increased intensity of pain with a normally painful stimulus, or feeling pain with stimuli that shouldn't normally create pain at all, such as light touch. In medical terms, these are described as Hyperalgesia and Allodynia.
This 'wind-up' of pain is known as central sensitization.
(Think of a house alarm system and its sensitivity- sometimes it may only go off when a fox walks by, sometimes it could go off with just a small leaf dropping).
This is the phenomena we believe to play a role in conditions such as Fibromyalgia, Complex Regional Pain Syndrome & Irritable Bowel Syndrome.
How may we know if our nervous system is 'learning pain' and becoming over-active?
The pain may spread, come on without warning, old injuries may start to hurt again, you may become more sensitive to pain, pain may change with your mood and be easily triggered, it may be hard to move easily or your body may feel 'odd'.
Naturally, we'd think that to hurt so badly, there must be a significant issue in the tissue, yet this is not always the case when we look at imaging studies (for example, many patients with disc issues seen on MRI scans have no symptoms and some patients with only mild imaging findings have a lot of pain).
Descending Inhibition
As well as a 'wind up' of pain that can happen, a 'wind down' of pain can also occur with a process called Descending inhibition. Descending Inhibition is caused by the release of chemicals such as Opioids and Serotonin, which decrease pain. These are the chemicals used in a number of pain medications such as Codeine and some Anti-depressants. A number of other factors can also help activate the descending inhibition pathway...
How can we help retrain our nervous system and decrease sensitivity?
In chronic pain conditions, a multi-disciplinary approach is often key. Due to the fact that nervous system sensitization can take place due to increased physical, psychological and chemical stimuli, all of these factors need to be considered...
Physical factors- hands on treatment and home exercises can help 'close the pain gate'. Gentle aerobic exercise is particularly beneficial. (See my blog posts on 'The Lesser known Benefits of Exercise' and 'Spinal Manipulation- what's the Crack?' for the mechanisms behind this).
Psychological factors- Cognitive Behavioral Therapy (CBT), or other psychological approaches such as Hypnotherapy and Counselling can help decrease stress, anxiety and depression. Social factors such as loneliness also need to be taken into account.
Chemical factors- such as inflammation caused by poor dietary habits (e.g. high in processed foods) or gut dysbiosis, low Vitamin D and Magnesium, smoking and excessive alcohol intake, obesity and metabolic syndrome, poor sleep (which can largely exacerbate sensitivity and pain) and potentially toxins such as mold/mercury may need to be addressed. (See my blog posts on Nutrition, Sleep and Stress to understand how these factors can increase inflammation and therefore sensitivity to pain).
Key Points:
A Biopsychosocial approach in understanding pain is key in many patients, especially with chronic pain and in conditions such as Fibromyalgia.
Therefore, taking a multi-disciplinary approach in treating pain is very important- looking at physical, psychological/social and chemical factors.
Pain is not always a sign of tissue damage but more an individual response to threat, real or perceived. Pain is a warning signal and sometimes it is needed, but often our brains can end up producing unnecessary warning signals and being too protective.
Over time our bodies may 'learn pain' due to certain unique stimuli. This is linked with Conditioning (think of Pavlov's dogs). These stimuli may have been unconsciously building up over years for some patients.
Therefore, it is not always easy to change these chronically conditioned pain states. But understanding the science behind it is the first step!
Educating patients about pain is important.
Evidence behind Pain Science Education:
A randomised controlled trial has shown that one-to-one education sessions about the neurophysiology of pain will result in significant changes in pain beliefs and attitudes (Moseley, 2002).
Pain thresholds can be increased during physical tasks (Moseley, 2004.)
Pain neurophysiology education will improve the outcome of other therapeutic approaches such as various exercise strategies (Moseley, 2003b).
More recent studies (eg. Meeus et al 2010; Nijs et al 2011, Kol et al. 2013) have supported the initial Moseley et al. findings with the increased number of studies now allowing initial systematic reviews which support the use of Explain Pain type education, in particular, to decrease pain ratings, perceived disability and catastrophisation, and developing healthy attitudes and beliefs about pain (Louw et al. 2011; Clarke et al. 2011).
In conclusion, pain science is a fascinating and growing concept, which should be explained to patients. This may be relevant not only in helping patients already with chronic (longstanding) pain, but in stopping patients in acute (short term) pain from developing chronic pain conditions. As always, some patients may benefit form this education more than others and every patient is unique in terms of what factors may need to be addressed!
Other Helpful Links:
https://www.tamethebeast.org/#tame-the-beast - Patient friendly video explaining Pain
https://www.rcplondon.ac.uk/guidelines-policy/diagnosis-fibromyalgia-syndrome- New Guidelines on Fibromyalgia diagnosis and management
http://www.protectometer.com/ - Book or App teaching patients about pain and helping them track their thoughts
https://www.painscience.com/index-pain-theory.php - Website including articles/blogs about all things pain science related
https://www.physio-pedia.com/Descending_Pathways - Descending inhibition evidence and explanation
https://physio-pedia.com/Pain_Facilitation_and_Inhibition - In depth neurobiological explanation of the Pain Pathways
s-lanss.pdf (bpac.org.nz)- LANSS Scoring System for Neuropathic Pain
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