An international multicentre validation study of a pain classification system for cancer patients

Abstract

Purpose

The study’s primary objective was to assess predictive validity of the Edmonton Classification System for Cancer Pain (ECS-CP) in a diverse international sample of advanced cancer patients. We hypothesised that patients with problematic pain syndromes would require more time to achieve stable pain control, more complicated analgesic regimens and higher opioid doses than patients with less complex pain syndromes.

Methods

Patients with advanced cancer (n = 1100) were recruited from 11 palliative care sites in Canada, USA, Ireland, Israel, Australia and New Zealand (100 per site). Palliative care specialists completed the ECS-CP for each patient. Daily patient pain ratings, number of breakthrough pain doses, types of pain adjuvants and opioid consumption were recorded until study end-point (i.e. stable pain control, discharge and death).

Results

A pain syndrome was present in 944/1100 (86%). In univariate analysis, younger age, neuropathic pain, incident pain, psychological distress, addictive behaviour and initial pain intensity were significantly associated with more days to achieve stable pain control. In multivariate analysis, younger age, neuropathic pain, incident pain, psychological distress and pain intensity were independently associated with days to achieve stable pain control. Patients with neuropathic pain, incident pain, psychological distress or higher pain intensity required more adjuvants and higher final opioid doses; those with addictive behaviour required only higher final opioid doses. Cognitive deficit was associated with fewer days to stable pain control, lower final opioid doses and fewer pain adjuvants.

Conclusion

The replication of previous findings suggests that the ECS-CP can predict pain complexity in a range of practice settings and countries.

Introduction

Pain is one of the most prevalent and distressing symptoms in patients with advanced cancer. Approximately 70% of these patients will experience pain at some point during the progression of their disease.¹ Although most patients achieve adequate pain control,2, 3 some – particularly patients with more complex pain syndromes – fail to obtain satisfactory analgesia. For these patients, clinicians may need to adopt a more intense and complex programme of therapeutic intervention, and as a result, more time is often required to achieve adequate pain control.⁴

Standardised approaches for assessing and classifying cancer pain need to be developed to identify and treat patients with complex pain syndromes. However, the complex, multidimensional nature of cancer pain presents unique challenges for pain classification. A review of the cancer pain literature has revealed the difficulty in comparing research results of analgesic management for cancer pain, due to the lack of a standardised approach.⁵ Diverse interpretations of the pain experience, as well as many factors that may contribute to it, have impeded the development of a standardised classification system. Although better characterisation and classification of pain syndromes would allow for more valid clinical and research comparisons, there is no universally accepted pain classification tool.6, 7

The development of a standardised classification system that is comprehensive, predictive of difficulty in achieving analgesia and simple to use could provide a common language for the clinical management and research of cancer pain. Bruera and colleagues recognised the need for such a system, prompting the development of the Edmonton Staging System (ESS).8, 9 The ESS has been used in a number of reports where it was found useful in describing the underlying cancer pain syndrome.10, 11, 12, 13, 14, 15, 16 Interpretational difficulties with analgesic prognosis and feature definitions have limited the international acceptance of the ESS. To overcome these limitations, an expert panel, consisting of physicians and researchers in the Edmonton Regional Palliative Care Program, developed the revised Edmonton Staging System (rESS). We have subsequently conducted five validation studies: a pilot study, a regional multicentre study,¹⁷ secondary analysis looking at pain intensity,¹⁸ opioid escalation¹⁹ and a construct validation study for validating definitions using an expert panel.²⁰ Based on feedback generated by the latter study and to reflect the intended use as a classification system, the amended instrument was renamed the Edmonton Classification System for Cancer Pain (ECS-CP).²¹ The ECS-CP includes five features – pain mechanism, incident pain, psychological distress, addictive behaviour and cognitive function (Appendix A). These features and the definitions and guidelines for use are the basis of the ECS-CP (Appendix B).

Using the revised definitions for the ECS-CP pain features,²¹ the primary objective of this study was to assess the predictive validity of the ECS-CP as a tool for classifying cancer pain in a diverse international sample of patients, who were referred to palliative care services. Our hypothesis was that patients with more problematic pain features, as classified by the ECS-CP, would require a longer time to achieve stable pain control, require more complicated analgesic regimens and use higher opioid doses than patients with less complex pain syndromes.