October 26, 2021
The topic of how we define pain, and how humans respond to pain has come...

The topic of how we define pain, and how humans respond to pain has come up for me as I mull over the IASP definition of pain. The current (new) definition is this:

An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.

Six key notes:

  • Pain is always a personal experience that is influenced to varying degrees by biological, psychological, and social factors.
  • Pain and nociception are different phenomena. Pain cannot be inferred solely from activity in sensory neurons.
  • Through their life experiences, individuals learn the concept of pain.
  • A person’s report of an experience as pain should be respected.
  • Although pain usually serves an adaptive role, it may have adverse effects on function and social and psychological well-being.
  • Verbal description is only one of several behaviors to express pain; inability to communicate does not negate the possibility that a human or a nonhuman animal experiences pain.

Now, for me the definition works fine – definitions describe and establish boundaries around what is being defined. Definitions don’t have to include all the uses of the term but instead just have to be distinct and clear, to “express the essential nature of something” as Merriam-Webster puts it.

Alongside this definition are notes about the function of pain – in other words, the notes (but not the definition) attempt to indicate why we experience pain. ‘An adaptive role‘ – in other words, pain serves a purpose in most cases and it may have adverse effects.

The question that leaps out to me now is what is the adaptive purpose of pain? This is the question that vexes many commentators who really don’t like the idea of what one author has called “maldynia“. Maldynia is thought to be “bad pain” that is severe, disabling and long-lived. I’m not fond of the word, but I do think there are pains that are not “adaptive” and these are amongst the ones that puzzle us the most in clinical practice. Things like phantom limb pain, nonspecific low back pain, complex regional pain syndrome and dear old fibromyalgia.

Back to the adaptive purpose of pain. Right now I have a cracked area on my heel. It’s quite a deep crack and it hurts every time I put my foot down. The way I’m using that information (the ‘ouch’) is to notice that yep, the crack is deep and there is tissue damage. And I am doing something about it by looking for urea-based cream and covering it while I work in the garden. I’ve (1) noticed tissue damage; (2) recognised that I need to do something about it; and (3) from experience, know that it will settle down and no longer be painful once the tissues have healed. I’ll also take care in the future to treat my heels so they remain soft as a baby’s bottom.

The metaphor of pain as an alert and action prompt serves quite well for me at the moment. And in most cases this is how we experience pain. Another example: I burned my thumb and finger on a soldering iron recently – you bet that hurt! I let go of the soldering iron PDQ, soaked my thumb and finger in cold water, then covered them until they had healed. The pain I experienced settled down after a day or so (unless I held a hot coffee cup!), and the new skin was a little tender for a couple of weeks. Again – pain served a purpose to alert me to stop doing dumb stuff, to protect the area, and to learn not to grab hold of the wrong end of the soldering iron! The metaphor of pain as an alert, call to action and learning experience again worked pretty well.

Now over the last few years I’ve had shoulder pain, imaging showed a bit of an enlarged bursa, a tiny fragment of calcification. This pain hasn’t settled down, even after I had cortisone injection AND did all the movement stuff including strength (yes – I did strength stuff!). Where oh where is the purpose or function of pain in this instance? Pain is not serving me well – I’ve been alerted, I’ve acted on that alert, nothing has changed and the metaphor breaks down.

But let’s take a look at the notes from IASP again – “Although pain usually serves an adaptive role” – usually. Usually. So there are times when pain does not serve an adaptive role. I think my shoulder pain, my groin pain, and my neck and back pain (yep, good old fibromyalgia) does not serve a function. I can’t think of any utility in having a grumpy body that really gripes about doing everyday movements like getting dressed, standing up from a chair, turning to look our the rear window of my car while I reverse down the driveway or aches in different parts of my body on different days then moves somewhere else at random.

A hidden assumption of the pain definition notes is that the “adaptive role” is reserved for those with a normally functioning nervous system, and where pain is associated with nociceptive activity, or inflammation. What if a nerve itself is damaged? What if the spinal cord is diseased or traumatised? What if there are changes to the way the nervous system processes information (we have that in every other sensory process, and in every other body system)? The experience of pain remains the same – still the same old aching, burning, gnawing, stinging sensations and the “ew”, “I don’t want this”, frustrating, totally unpleasant sensory and emotional experience as defined. The adaptive function, however? Not present.

The thing is, while I focus on persistent pain, most pain by far is not ongoing. I expect my heel crack to heal and the pain to go, and my now-slightly scarred finger and thumb are fine now.

Yes, the epidemiology of persistent pain shows that the prevalence of pain that goes on for more than three months is between 13–50{81fee095584567f29e41df59d482e70712cfc555e382220efc71af2368c27a36} of adults in the UK. Of those who live with chronic pain, 10.4–14.3{81fee095584567f29e41df59d482e70712cfc555e382220efc71af2368c27a36} were found to have moderate-to-severe disabling chronic pain (Fayaz, Croft, Langford, Donaldson & Jones, 2016). Similar findings for New Zealand – 16{81fee095584567f29e41df59d482e70712cfc555e382220efc71af2368c27a36} of NZers live with pain lasting three months or more.

But given I think most of us will hurt ourselves at least once this year (especially with the lockdowns and stress of COVID19 and the economy and elections…), this means that more often than not, our experiences of pain are the acute kind. The ones that do alert us to notice what’s happening in our body, to take some kind of action, and to learn something useful from this experience.

So, while the metaphor of an alarm, alert, “danger signal” or “bear” or “beast” doesn’t hold up for all of our pain experiences, on the whole, it works. And the purpose of metaphor is “a way of conceiving of one thing in terms of another, and its primary function is understanding” (Lakoff and Johnson, 2003). Ultimately, we use metaphors like these to generate a sense of purpose for an experience that is commonplace, and the most common pain we have is a short-term, temporary one. Let’s not let my bias towards persistent pain lead me astray.

Fayaz A., Croft P., Langford R., Donaldson J., Jones G. Prevalence of chronic pain in the UK: a systematic review and meta-analysis of population studies. BMJ Open. 2016;6

Lakoff G, Johnson M. Metaphors we live by. Chicago: University of Chicago Press, 2003:36.

Merskey H., Bogduk N., editors. IASP task force on taxonomy, Part III: Pain Terms, A Current List with Definitions and Notes on Usage. IASP Press; Seattle, WA: 1994. pp. 209–214.