Affective aspects of pain. A dummies’ guide to what it is and how might exercise help

This is a supplementary blog and dummies’ guide to a paper first published online in the BJSM in 2018. Smith BE, Hendrick P, Bateman M, et al. Musculoskeletal pain and exercise—challenging existing paradigms and introducing new British Journal of Sports Medicine 2019;53:907-912.

It formed part of a chapter in my recent PhD that looked at the assessment and management of patellofemoral pain. As such, my work is a product of supervision and collaboration.  So I would like to start by acknowledging and thanking my supervisors Pip Logan and Paul Hendrick, and collaborators Marcus BatemanSinead HoldenChris LittlewoodFiona MoffattMichael Rathleff, James Selfe and Toby Smith.

Introduction – What is it?

Affective aspects refer to thoughts, feelings and attitudes.

Negative affective aspects of pain are often called pain-related fear. And can be viewed as an umbrella term encompassing a range of negative emotional states. These include

  • kinesiophobia (fear of pain during movement, or fear of physical movements);
  • fear-avoidance (negative thoughts towards movements and fear of injury/pain);
  • catastrophizing (exaggerated negative thoughts);
  • low self-efficacy (low confidence in coping with the pain and completing tasks);
  • anxiety (feeling of worry or nervousness), and
  • depression (low mood) [4,6].

Pain-related fear is becoming increasingly recognised in a range of MSK disorders, such as long term

  • back;
  • hip;
  • knee;
  • patellofemoral pain; and
  • shoulder pain [4,6,12,25].

How does it link to pain and central sensitisation?

Research has shown that pain-related fear not only reduces function and quality of life in patients with pain but can alter people’s pain [5,7,11,16–18,20].

It does this by amplifying the experience of pain. For example, there is strong evidence that pain is experienced more strongly when someone pays it more attention [1–3,8,22].

There is also research that has demonstrated that beliefs and attitudes to pain, and what constitutes “threatening” pain or not, changes the way people move and behave [21].

The mechanisms by which pain-related fear is thought to influence central sensitisation are:

  1. increasing nociceptive transmission via spinal gate mechanism [26];
  2. via modulation of the descending pathways [26]; and
  3. temporal summation, where the increasing magnitude of spinal dorsal horn neurons activation increases glutamine sensitivity. Resulting in a pain response disproportionate to the stimulus experienced [20,27].

Further details on this process can be read in our paper Musculoskeletal pain and exercise—challenging existing paradigms and introducing new British Journal of Sports Medicine 2019;53:907-912.

What’s the role of the amygdala?

Evidence from neuroimaging has demonstrated the role of the amygdala (the area of the brain associated with fear and the response to fear)  in pain-related fear, and its potential over-activity, as a facilitator of pain and central sensitisation  [9,10,24].

For example, Laura Simons et al.’s review on The Human Amygdala and Pain: Evidence from Neuroimaging provides an excellent overview of neuroimaging pain studies and how the amygdala is implicated in acute and persistent pain [24]. The review’s meta-analysis supports the role of the amygdala in pain processing and suggests that targeted therapies that may modulate amygdala function should be developed and evaluated.

Research has even demonstrated that even mental preparation for movements and activities can trigger the fear-memory centre of the brain; thought to be an overactive threat protective mechanism, triggering pain, in the apparent absence of nociception [29].

How does exercise help?

A major consideration of the beneficial effects of exercise is the associated learning involved.

Exercises could help challenge patients to think differently about pain and movement. With exercises offering an opportunity for patients to learn to tolerate movements and activities they feared gradually. Using exercise to help people think differently about pain-related fear may help learn a new inhibitory response [13]. These new inhibitory associations compete with the original overactive response so that they become suppressed [13].

Figure 1 from Musculoskeletal pain and exercise—challenging existing paradigms and introducing new British Journal of Sports Medicine 2019;53:907-912.

bjsports-2019-July-53-14-907-F1.large
The role of exercises in the management of chronic musculoskeletal pain. Therapeutic exercise challenges the threat response to pain. Central pain processes, the immune system and affective aspects of pain may respond differently when pain is conceptualised as non-threatening. Adapted from Physiotherapy, 84(1), Gifford, Louis., ‘Pain, the tissues and the nervous system: a conceptual model’, 27–36, Copyright (1998), with permission from Elsevier.

How do we know this?

Research supporting this hypothesis has come from animal studies [14,15], that have reported the involvement of the medial prefrontal cortex (mPFC) in the learning of new inhibitory associations, which has direct projections onto the amygdala [13]. Human studies on military personnel with and without a clinical diagnosis of posttraumatic stress disorder (PTSD) have confirmed this inverse relationship between activity in the mPFC and amygdala [23].

Clinically, it is worth noting, that this process does not indicate the retraction of the original overactive response (pain-related fear has never truly been eliminated). But that new inhibitory associations compete with the original response. It may, given certain conditions, for example, during an acute flare-up, resurface.

Further details on this process can be read in our paper Musculoskeletal pain and exercise—challenging existing paradigms and introducing new British Journal of Sports Medicine 2019;53:907-912.

Self-efficacy may also be used to explain fear reduction. The potential mechanisms behind the effect of exercises are thought to be that exercises may alter both the response-outcome and efficacy expectation, both components of self-efficacy [28].  Within the context exercises moving from easier to more difficult/higher load, where the patient begins to recognise that they can tolerate harder exercises, without triggering the previous experience of pain-related fear, and pain flare-ups [19]. Furthermore, exercises (with appropriate progression) provides evidence to the patient that they are systematically approaching goals [19].

Found this blog useful? Want to learn a contemporary, evidenced-based approach to the assessment and management of patellofemoral pain? Have a look at available course dates and information. tile

Summary

Central pain processes (central sensitisation), the immune system and affective aspects of pain appear to play a role in the development and maintenance of persistent pain. Therapeutic exercise seems to have an affect of these three overlapping systems.

I hope you’ve found this dummies’ guide to the immune system in persistent pain and principles of exercise for pain-related fear helpful.

References

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