In July 2020, the International Association for the Study of Pain (IASP) updated its 40-year-old definition of “pain.” PPM talked to members of the Task Force behind the rewrite, published in Pain.1
Here’s a quick look at what changed:
Old definition: An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
New definition: An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.
Updated Notes accompanying the new definition:
- 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.
Responding to the questions below are:
- Task Force Chair Srinivasa N. Raja, MD, director of Pain Research, Professor of Anesthesiology & Critical Care Medicine, Professor of Neurology, Johns Hopkins University School of Medicine
- Task Force Member Jeffrey Mogil, PhD, director of the Alan Edwards Center for Research on Pain, McGill University
- Task Force member Nanna Finnerup, MD, PhD, Department of Clinical Medicine, Danish Pain Research Center and Department of Neurology, Aarhus University, Denmark
Why Redefine Pain Now?
PPM: What specific knowledge areas in the understanding of pain came about that urged the task force to make this change? In other words, why make this change now?
Dr. Raja: The original IASP definition, written in 1979,2 has been accepted globally by healthcare professionals and researchers in the pain field, and adopted by several professional, governmental, and nongovernmental organizations, including the World Health Organization (WHO). Although the list of associated pain terms have been revised and updated in more recent years, the IASP definition of pain itself has remained unchanged for four decades. Over the years, several advances in our understanding of pain in its broadest sense have warranted a re-evaluation of the definition.
Some of the criticisms of the [older] IASP definition have included that it is “Cartesian” – ignoring the multiplicity of mind–body interactions, and that it neglects “the ethical dimensions of pain.”
In addition, the earlier definition has been interpreted as emphasizing verbal self-report [from patients] and excluding non-verbal behaviors indicative of pain in disempowered and neglected populations, such as neonates and the elderly. In addition, it did not take into consideration the cognitive and social factors critical to the pain experience.
Finally, research in more recent years has indicated that some types of pain (namely, nociplastic pain) exemplified by conditions such as fibromyalgia and irritable bowel syndrome, may not be associated with tissue injury and may be associated with nervous system dysfunction. The Task Force focused on addressing these criticisms in the revised definition and its accompanying notes (numbered 1-6 above).
In revising the definition, the Task Force sought input from multiple stakeholders, including clinicians, researchers, philosophers, and the public – which included persons with pain and their caregivers.
Focusing on the Pain Experience and the Experiencer
PPM: The new definition has a very minor change in words, along with the new six points – what was the reasoning behind these few words?
Dr. Mogil: The change in words solves a significant problem with the existing definition. In the old definition, the word “described” in the phrase “or described in terms of such damage” seemed to imply that verbal communication (what, after all, is a “description” other than verbal communication?) was required for pain to exist. This is no longer the consensus of the scientific and clinical pain communities, which have agreed now for some time that non-verbal organisms (eg, babies, adults with dementia) are perfectly capable of experiencing pain.
The new definition’s wording – “or resembling that associated with…” – does not require any verbal description. It also places the onus for perceiving pain on the experiencer of that pain, whereas in the old definition, part of that responsibility would lie with whomever heard the description. This change too is in keeping with current best practices regarding believing pain patients when they assert that they’re in pain.
Dr. Raja: Although the changes in the definition might seem minor, considerable changes were made in the Notes that accompany the definition to reflect current scientific understanding of pain. These included deletion of the sentence in the previous Notes that stated: “pain in the absence of tissue damage or any likely pathophysiological cause” was usually due to psychological reasons.
Pain Beyond Nociception
PPM: Can you expand on Note #2 which states, “Pain and nociception are different phenomena. Pain cannot be inferred solely from activity in sensory neurons.”
Dr. Mogil: Pain, like all other sensations and emotions, is mediated by neurobiological circuits in the nervous system. In many (but not all) cases, information about actual or potential tissue damage in the periphery is brought to the brain via sensory neurons (“nociceptors”). Thus, pain as the experience is often produced by nociception – the activity of nociceptors (and other neurons in the nervous system). There is thus an understandable motivation to try and simplify how pain works by focusing on activity in those sensory neurons.
Current scientific evidence would suggest that this is a mistake, however. Pain levels cannot be accurately inferred from levels of activity in sensory neurons. Pain is much more than nociception.
Tissue Damage, Neuropathic Pain, and the ICD-11 Definitions of Pain
PPM: How does the updated IASP definition align with the ICD-11 reclassification of chronic pain, set to take effect in 2022?
Dr. Finnerup: The ICD-11 is the latest revision of WHO’s International Classification of Diseases adopted in 2019. It includes for the first time a classification of chronic pain. The new definition of pain and the classification of chronic pain in ICD-11 are two important and aligned steps with the aim to improve the understanding of pain and multimodal treatment of pain.
The ICD-11 chronic pain classification codes for seven main chronic pain diagnoses. In alignment with the new definition, the ICD-11 classification acknowledges that chronic pain may or may not be associated with tissue damage (see Treede, et al. Pain 2019).
As an example of pain related to tissue damage and activation of nociceptors, chronic secondary musculoskeletal pain is pain in muscles, bones, joints, or tendons that arises from an underlying disease, such as persistent inflammation in rheumatological diseases or structural changes in osteoarthritis (see Perrot, et al. Pain. 2019).
Neuropathic pain, on the other hand, is defined as pain caused by a lesion or disease of the somatosensory nervous system and is not caused by activation of nociceptors.
Another example of a pain diagnosis not related to tissue damage is chronic primary pain, which is defined as pain associated with emotional distress or functional disability and that cannot be better accounted for by another chronic pain condition (see Nicholas, et al. Pain. 2019) Subdivisions of this diagnosis include fibromyalgia, irritable bowel syndrome, and chronic primary musculoskeletal pain, which is contrast to chronic secondary pain, is not attributed to a known disease or damage process with activation of nociceptors.
The inclusion of this diagnosis in ICD-11 has the advantages of minimizing unnecessary diagnostic procedures, early focus on managing impact of pain, and greater potential for a patient-centered approach (see Smith, et al. Pain. 2019.)
In summary, the new IASP definition is an attempt to include pain of different etiologies and mechanisms consistent with the new ICD-11 classification of chronic pain.
PPM: What takeaways can pain practitioners gather from the updated IASP pain definition – is the goal is to focus more on patient communication using a biopsychosocial approach?
Dr. Raja: IASP and the Task Force wrote the revised definition and related Notes with the hope that a better understanding of the multiple factors that contribute to an individual’s experience of pain may lead to better communication between the patient and the provider and result in improved assessment and management of their pain.
The revised Notes to the definition emphasize that pain may have adverse effects on function and social and psychological well-being. We also hope that the revised definition will encourage the person in pain to convey a more complete picture of the adverse effects of their pain to their care providers.
Similarly, we are optimistic that the revised definition may lead the clinician to not only listen to the patient’s complaints of pain, but also to inquire as to how the individual’s pain interferes with their daily activities, quality of life, relationships, and social interactions. This information will facilitate the provider in developing a personalized, multidisciplinary, patient-centered pain management strategy.
1. Raja SN, Carr DB, Cohn M, et al. The revised International Association for the Study of Pain definition of pain. Pain. May 23, 2020. In Press. Available at: https://journals.lww.com/pain/Abstract/9000/The_revised_International_Association_for_the.98346.aspx
2. Merskey H, Albe Fessard D, Bonica JJ, et al. Pain terms: a list with definitions and notes on usage. Recommended by the IASP subcommittee on taxonomy. Pain. 1979;6:249-252.