Background: Bone metastasis results in disabling pain, negatively impacting on quality of life. A better understanding of its characteristics may assist in achieving stable pain control.
Aims: To evaluate the characteristics of cancer induced bone pain and its associations using a standardised international system, the Edmonton Classification System for Cancer Pain (ECSCP).
Methods: Average and worst pain intensity were recorded using the 11-point numerical rating scale on adult cancer patients with bone metastasis. Validated measures were used to elucidate pain mechanisms, cognition, addictive behavior and psychological distress. Negative features from all components of ECSCP were summed to calculate a composite score. Opioid analgesia usage was recorded.
Results: Among 101 eligible patients, 87 completed questionnaires and 3 had no pain symptom (N=84). Mean (SD) for average and worst pain were 2.96 (2.54) and 5.18 (3.82) respectively. After adjusting for age and sex, one unit increase in the composite score resulted in a 1.55 (95% CI: 1.20 to 1.90; P<0.001) unit increase in average pain and 2.6 (95% CI: 2.10 to 3.11; P<0.001) unit increase in worst pain. Both pain scores were positively associated with nociceptive/neuropathic pain (mean difference (MD) of 3.9 and 6.8, p <0.001) and the presence of incident pain (MD: 2.2 and 4.7, p <0.001). Incident pain was associated with higher oral morphine equivalent daily dose (OMEDD) of background opioid (MD: 19.4mg, p=0.002). Addictive behavior was associated with increased frequency of opioid breakthrough usage (MD: 0.9, p=0.02). No association was observed between OMEDD of background opioid and pain mechanism or addictive behavior; frequency of opioid breakthrough usage and pain mechanism. Psychological distress and cognitive impairment were not associated to pain intensity or opioid usage.
Conclusion: A strong positive association was found between ECSCP features and pain reporting scores by patients with bone metastasis.