Support for extended classification of pain states

We welcome the recent review “Do we need a third mechanistic descriptor for chronic pain states?” byKosek et al. and their invitation toexpand thisdiscussion to thewiderpaincommunity.Weareacutely aware of the need for internationally agreed pain terminology that is consistent, widely recognised, clinically useful, and allows for iteration as more research emerges regarding our understanding about pain. As Kosek et al. highlight, current approaches impose a binary classification between nociceptive pain and neuropathic pain. The authors also outline emergent issues associated with the recent redefinition of neuropathic pain by the IASP in 2011 and the associated clinical criteria for classifying neuropathic pain, leaving a substantial proportion of patients with pain unclassified. As clinical and research physiotherapists working with people with musculoskeletal pain and disability, we agree that this current binary system fails to acknowledge, or apply to, a sizeable subgroup of our clinical population. In clinical practice, this has many possible adverse consequences including: (1) inadequate recognition of patients whose pain cannot be classified within the current binary system; (2) less effective communication between clinicians and patients about the nature of their pain; (3) less informed consideration of treatment choices; and (4) potential for an unhelpful focus on peripheral tissue dysfunction to explain why pain persists. Kosek et al. suggested the following 3 proposals: (1) the assertion of nociceptive pain, (2) confirmation of the definition of neuropathic pain (but not as default), and (3) the need for a third mechanistic descriptor for people living with chronic pain that may serve to address some of the issues highlighted. With respect to items 1 and 2, we agree with current definitions and that pain classifications of nociceptive pain and neuropathic pain should not be dichotomous. With respect to item 3, we strongly support the arguments made for a third descriptor. It may be useful to note that some of us have previously published frameworks and models that attempt to address this issue and provide support for an expanded classification system of pain. As the topical review by Kosek et al. was positioned as a proposal welcoming debate, we would like to contribute by raising the following points: Point 1. The intention of the third descriptor described by Kosek et al. is “... to distinguish patients suffering from conditions where alterednociception hasbeendocumented from thosewhere thepain mechanisms are still truly unknown.” This raises the following issues: (1) While the focus in this review addresses chronic pain states, could the third descriptor also apply in acute pain states, given that abnormal functioning of the nociceptive system may also be apparent in some people with acute pain? (2) Pain “descriptors” in this classification systemmaynot necessarily be synonymous with the reasons for, or reflect all mechanisms underlying, ongoing pain, that is, there are multiple dimensions involved in characterising chronic pain, and descriptors may be helpful but only in the context of the whole clinical presentation. Therefore, classification of pain by descriptive terms is only one part of a broader framework for understanding the lived experience of pain, including psychosocial, lifestyle, genetics, and environmental factors that may contribute to sensitisation processes. How will a third descriptor (and requisite clinical criteria to satisfy the application of this descriptor) be acknowledged within a broader (biopsychosocial) framework? (3) Ideally, a third descriptor would not imply an algorithmic approach to care that focuses on the descriptor classifications alone or dominantly without considering this broader context. Perhaps, subsequent discussion could include how the addition of the third mechanistic descriptor be applied within the broader pain experience to guide treatment. Point 2. Information regarding what processes will be engaged to progress this proposal would bewelcome. Is this an IASP taxonomy committee task, and if so, how will the wider clinical and research community be engaged (eg, the use of a Delphi process, which could also capture perspectives on relevant clinical criteria that may characterise a third descriptor)? Previous research has adopted similar approaches to identify characteristics of centrally mediated pain in musculoskeletal conditions, yet further work is likely needed to develop broader consensus that has clinical applicability. We would welcome further discussion on this topic, and specifically the issues raised.