Defining Chronic Pain by Prognosis

Kate M. Dunn, Michael Von Korff, and Peter R. Croft

This book addresses the transition ‘from acute to chronic back pain’, but do we really know what ‘chronic’ means? The International Association for the Study of Pain (IASP) defines chronic pain as pain lasting beyond the normal healing time, which is usually defined as 3 months or 6 months (International Association for the Study of Pain 1986). Is this retrospective approach to defining chronic pain sufficient, or are there better ways to characterize patients with chronic pain? In this chapter we reconsider the duration-based, retrospective approach to defining chronic pain, consider reasons why it might be inadequate, and develop an alternative approach to assessing and defining chronic pain, based on its prognosis and multiple prognostic indicators grounded in the biopsychosocial model of pain.

The prognostic approach to defining chronic pain developed in this chapter rests upon three propositions that can be tested empirically. The first proposition is that chronic pain is better characterized by a failure of pain and associated dysfunction to resolve than by progression to a qualitatively distinct chronic pain state. That is, severe pain, pain-related activity limitations, psychological distress, and other features used to characterize chronic pain patients are observable soon after pain onset. What typically differentiates ‘chronic pain’ from ‘acute pain’ is that severe pain and associated dysfunction does not show meaningful improvement. While progressive worsening of pain and pain dysfunction may be observed in some patients, this clinical course is less common. The second proposition is that the seeds of chronic pain (prognostic indicators) are observable early in the course of a pain condition, providing a basis for early identification of patients at risk of an unfavourable outcome. The third proposition is that varied and multi-faceted prognostic indicators can be summarized in a single measure—a prognostic risk score. This prognostic risk score measures how likely it is that clinically significant pain will continue to be present at a future point in time, providing a simple and clinically relevant metric for quantifying chronic pain in terms of its future prognosis rather than its past duration considered in isolation.