Making a definition of pain work for us

With our new proposal, we are not, emphatically NOT, suggesting that we have arrived at the ideal definition of pain. A definition needs to work for clinical and experimental pain, for humans and for other animals, for excruciating and for trivial pain. It needs to distinguish pain from all other sources of distress, from specific anxieties to existential angst or profound grief.

What we hoped we could do with our Topical Review in Pain [1] – and my co-author, Kenneth Craig, has approved this piece for Body in Mind – was to invite (provoke?) a discussion about updating the IASP definition, and to get clinicians and researchers with expertise in all these areas, and more, to pile in and add their ideas. Out of this, we hope, will come a revised definition that works better.

The existing definition (see below) has been rendered out of date by the very research that it has helped to foster. We have both cited the existing definition, in papers and in teaching, more times than we could possibly count, and have done so because it has served very well. But it does have flaws and gaps that are increasing with age.

What are they?

  • Cognitive and social effects are increasingly evident not only in humans but in, for example, rodents [2,3]; these effects have hardly been addressed in other animals but behavioural changes observed across species [4,5] lead us to expect to find them.
  • The emphasis on subjective report was very important, but so is behaviour, and defining pain in exclusively subjective terms makes it hard to apply to non-human animals.
  • We were concerned to represent the profoundly aversive nature of much clinical pain with a stronger term than “unpleasant” to capture the motivational elements, but of course much experimental pain and some procedural clinical pains (a routine immunisation in an adult, for instance) are mild in intensity, unthreatening because voluntarily undertaken, and quickly forgotten.

Adding cognitive and social components to the definition was straightforward, and we have had some encouragingly enthusiastic feedback about this. Those components, of course, may find behavioural expression, but the definition does not seem the place for attempts to encompass these behaviours in general terms. However, they are important and should be elaborated in a revised note.

The existing accompanying note (who reads this?) is important because it refers to the need to assess pain in people unable to provide self-report [6], such as infants and babies and people of any age with cognitive impairment. But it includes several statements that complicate or contradict the main definition (such as “Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons”(!)), and these need to be deleted.

So far, responses to our topical review have tended to raise philosophical issues around definition (which should make clear the way in which the construct defined is unique) and description (which is often an elaboration of the definition but without the requirement that it differentiates the construct from everything else). While this is important, we hope to generate discussion about how the definition is used, and how it could better meet users’ requirements. The existing IASP definition is very widely cited in the animal welfare literature and in debates about animals feeling pain; arguably, a more behavioural and less subjective definition would serve this important field better.

We also hope that we can engage those outside the fields of pain research and treatment. There is still widespread misunderstanding of pain. Patients are often wary of talking about the emotional impact of pain in medical consultations, or being referred to anyone whose profession starts with psych. Educated people frequently ask if by pain I mean “real/physical pain” or “emotional pain”. How can we build a definition that helps people to think in an integrated way about mind and body, rather than to start with this profoundly unhelpful and false dichotomy?

And did we mention that our definition is intended for discussion, revision, and improvement? We do not believe that we have yet found the perfect wording.

About Amanda C de C Williams

Dr Amanda WilliamsAmanda is an academic and clinical psychologist who has specialised in pain for thirty years. She works mainly at University College London researching and teaching; she also works with clinicians in the UCL Hospitals pain team, and in human rights. She is getting rather old and impatient with the rate of change of some ideas in the pain world, so she thought it was time to tackle the definition of pain.

Pain definition

An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

Note: The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain, and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain. This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause.

As updated from “Part III: Pain Terms, A Current List with Definitions and Notes on Usage” (pp 209-214) Classification of Chronic Pain, Second Edition, IASP Task Force on Taxonomy, edited by H. Merskey and N. Bogduk, IASP Press, Seattle, ©1994.  http://www.iasp-pain.org/Taxonomy#Pain

References

[1] Williams ACdeC, Craig KD. Updating the definition of pain. Pain 2016;157:2520-3.

[2] Mogil JS. The social modulation of and by pain in humans and rodents. Pain 2015;156(Suppl. 1):S35-41.

[3] Low LA. The impact of pain upon cognition: what have rodent studies told us? Pain 2013;154:2603-5.

[4] Walters ET. Injury-related behavior and neuronal plasticity: an evolutionary perspective on sensitization, hyperalgesia and analgesia. Int Rev Neurobiol 1994;36:325-427.

[5] Williams ACdeC. What can evolutionary theory tell us about chronic pain? Pain 2016;157(4):788-90. doi:10.1097/j.pain.0000000000000464

[6] Anand KJS, Craig KD. New perspectives on the definition of pain. Pain 1996;67:3-6.

Commissioning Editor: Lorimer Moseley;  Associate Editor: Adrian Traeger