The Revised IASP Definition of Pain and Accompanying Notes: Considerations for the Physiotherapy Profession

In 2020, for the first time since it produced its initial definition of pain in 1979,¹ the International Association for the Study of Pain (IASP) published a revised definition of pain and accompanying notes² (see Box 1 for the 1979 definition and note and Box 2 for the 2020 revision and notes). This revision is timely, given recent advancements in the field of pain, including the introduction of a newly defined mechanistic descriptor of pain (i.e., nociplastic pain) and updates to the International Classification of Diseases, 11th Revision (ICD–11), which states that chronic pain can be “a health condition in its own right.”^3,4(p.19) This revision was led by an IASP Task Force and was outlined in a recent publication.² In this editorial, we provide critical reflections on the revised IASP definition of pain and the accompanying notes and discuss considerations for physiotherapy practice, education, research, and policy.

Box 1. IASP (1979) definition of pain¹.

Pain

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

Note

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 which 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 (e.g., pricking), but are not unpleasant, should not be called pain. Unpleasant abnormal experiences (dysaesthesiae) 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 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.

IASP = International Association for the Study of Pain.

Box 2. Revised IASP (2020) definition of pain².

Pain

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

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.

Etymology

Middle English, from Anglo-French peine (pain, suffering), from Latin poena (penalty, punishment), in turn from Greek poinê (payment, penalty, recompense).

Critical reflections

A notable strength of this revision is that it removed the statement that pain in the absence of tissue damage or pathophysiological causes “happens for psychological reasons.”¹ This statement did not reflect current evidence and potentially contributed to stigma, an experience commonly reported by people with chronic pain.⁵ Moreover, removing the phrase “or described in terms of such damage” addresses previous concerns that the 1979 definition of pain relied too heavily on verbal self-report.^1,6 However, removing it may de-emphasize pain as an internal experience that a person communicates (verbally or non-verbally). As such, the revision could be perceived as placing a greater emphasis on pain as an experience that requires interpretation by an observer. Finally, the note “Through their life experiences, individuals learn the concept of pain” could have unintended consequences if incorrectly interpreted by health care providers, who might then blame the person for their current conceptualization of pain (e.g., that the person has learned the concept of pain incorrectly and is now catastrophizing).^2,7 However, these concerns are tempered by the notes, which identify pain as a personal experience that should be respected.

Considerations for practice

This revision has broad implications for physiotherapy practice. The fact that the notes acknowledge the impact of pain on function and well-being speaks to the role of pain management in addressing not only pain but also its associated negative consequences. This acknowledgement highlights the role of rehabilitation providers, such as physiotherapists, in comprehensive pain management that addresses the whole person. Moreover, the note “A person’s report of an experience as pain should be respected” emphasizes the importance of physiotherapists validating a person’s pain experience.^2,8 Dismissal of pain by health care providers has been identified as contributing to stigma for people with chronic pain,⁵ so we are hopeful that this explicit endorsement of respecting pain represents a positive step forward. Finally, the note “Verbal description is only one of several behaviors to express pain” guides physiotherapists to integrate non-verbal expressions of pain (e.g., pain behaviours) into their evaluation strategies,² especially for persons who may not be able to verbally communicate their experiences of pain, such as infants,⁹ persons with intellectual and developmental disabilities,¹⁰ and older adults with dementia.¹¹

Considerations for education

This revision can serve as a foundation for continued improvements in entry-level physiotherapy pain education, and it reinforces the value of work that is currently underway to advance pain education in Canadian physiotherapy programmes.¹² For example, a note refers to a person’s pain experience as being influenced by “biological, psychological, and social factors”;² this statement supports the ongoing shift toward a biopsychosocial model of pain, away from the historical emphasis on more biomedical understandings in the field of physiotherapy.¹³ Acknowledging the impact of psychological and social factors on pain also emphasizes the need for physiotherapy students to develop competencies in screening for such determinants and the knowledge to tailor their management strategies appropriately. Although psychologically informed approaches to pain management have historically been considered outside the physiotherapy scope of practice, there is now a growing recognition of their value.¹⁴ Thus, it is important to provide physiotherapy students with these skills so that they can fully address the complexity of pain.

Considerations for research

This revision provides an operational definition of pain for research in the field of physiotherapy. For example, the note “Pain is always a personal experience” supports the value of qualitative research and including narrative accounts of the subjective experience of pain in addition to traditional quantitative measures,^2,15,16 both of which have historically been undervalued. The recognition of function and well-being in the notes also supports the notion that research on physiotherapy interventions for pain conditions should continue to consider function and associated outcomes and not focus solely on pain intensity as the main indicator of treatment effectiveness. Finally, the note that pain can be influenced by “biological, psychological, and social factors” speaks to the complexity of pain and the importance of continuing research efforts to understand pain processing and the underlying mechanisms of interventions commonly used in physiotherapy practice (e.g., mechanisms of exercise-induced analgesia).¹⁷

Considerations for policy: a call to action

The revised notes refer to the Declaration of Montréal, whose Article 1 declares “The right of all people to have access to pain management without discrimination.”^{18(p. 29)} This declaration is reinforced by calls for improved chronic pain management in Canada (see a recent report by the Canadian Pain Task Force).¹⁹ Ultimately, this revision can serve as a critical opportunity for physiotherapists to take action and advocate for timely and equitable access to effective pain management. Targets should include other health care providers, policy- and decision makers, and third-party payers. Advocacy efforts are of particular importance, considering the lengthy waitlists and inequities in access to outpatient physiotherapy²⁰ and multidisciplinary pain management facilities in Canada.²¹

Summary

We believe that the revised IASP definition of pain and accompanying notes are an important milestone in the field of pain. We encourage physiotherapists to embrace and apply the concepts outlined in this revision, particularly the notes, because they provide essential information for understanding the complexity of pain. As suggested by the IASP Task Force,² this revision should be viewed as a living document that will be updated as new knowledge is acquired. In alignment with this, it is important for physiotherapists to seek out and apply this new knowledge, with the ultimate goal of reducing the burden of pain.