Defining Chronic Pain by Prognosis

Abstract

In this chapter, traditional duration-based approaches to defining chronic pain have been contrasted with multifactorial models of pain based in the biopsychosocial model. A new approach to defining chronic pain based on outcome probabilities that are a function of multiple prognostic indicators is proposed. We believe that this approach offers improved predictive validity, as well as better conceptual links to the biopsychosocial model, than approaches based on pain duration alone. It is consistent with current guidelines for managing chronic pain, and is likely to provide more useful information to patients and clinicians. As an alternative to the IASP definition of chronic pain, we propose that chronic pain be defined by the risk that clinically significant pain and associated dysfunction will be present at a future time point, where the likelihood of future pain and dysfunction is predicted by multiple prognostic factors. The prognostic indicators currently investigated for this purpose include pain severity, pain duration, number of anatomical pain sites, the severity of pain-related activity limitations, and psychological distress. However, these should not be considered as a restrictive or exhaustive list. Other prognostic indicators should be evaluated as they are identified or as the purpose fits, including psychological, psychophysical, and genetic variables. Such factors should be investigated and incorporated while keeping in mind that any assessment has to be acceptable and practical in the setting where it will be applied. The current approach, and any future extensions of the approach, will require testing in clinical practice to establish validity and utility outside the research setting. This definition of chronic pain based on risk of future clinically significant pain defines chronic pain status in probabilistic terms (possible and probable chronic pain), indicating to patients and providers alike that change in pain status over time, both improvement and deterioration, is common. This may help patients and clinicians to view chronic pain as a dynamic process, with potential for change, rather than a label applied to patients deemed unlikely to improve or hopeless. The fact that outcomes are a function of multiple factors calls attention to the possibility that chronic pain outcomes can be improved in ways other than reducing pain alone. The proposed prognostic approach should not be seen as representing a linear progression over time, although changes in any of the variables included in the risk score may indicate a transition between pain status categories. For example, an increase in the level of depression reported could move someone from having possible to probable chronic pain. Equally, a reduction in pain intensity could move someone from probable to possible chronic pain. Changes in the number of anatomical sites with pain or pain interference could also trigger shifts between categories of pain status. There is no underlying implication in the prognostic approach that pain sufferers progress from low risk through to probable chronic pain over time. This contrasts with a purely duration-based approach which, by its definition, implies deterioration in status or worsening prognosis over time, but is not based on strong empirical evidence and does not give further information on what should be done to improve outcomes other than eliminating pain. Using a definition of chronic pain based on pain duration alone seems inappropriate when biomedical, psychological and social factors are all accepted contributors to the experience, assessment, mechanisms and management of chronic pain. A definition based on prognosis, quantified in terms of outcome probabilities, encompasses both the complexity and the variability of pain, and appears to be more consistent with the biopsychosocial model of pain.