DESCRIPTION OF A MECHANISTIC APPROACH TO PAIN MANAGEMENT IN ADVANCED CANCER - PRELIMINARY-REPORT

A mechanistic approach to advanced cancer pain management is proposed, based on the clinically perceived anatomical and pathophysiological mechanisms of pain generation. It is an extension of the World Health Organisation (WHO) analgesic ladder in which severity of pain is the principal determinant of analgesic choice. The mechanistic categories are: superficial somatic, deep somatic, visceral and neurogenic (mixed or pure, i.e., nociceptive component present or absent). Allocation of pain to the different categories is based on clinical history, physical findings and investigations to establish the site and extent of active primary or metastatic tumour deposits, and evidence of previous response to medication. Drug choice sequence is determined by the dominant pain mechanism judged to be present and not the severity of the pain. In order to describe this approach, mechanisms of pain, disease distribution and drug treatment have been analysed in the first 20 consecutive patients who consented to enter a longitudinal pain description and evaluation study on admission to an inpatient hospice unit. Despite a high exclusion rate from research standard monitoring due to severity of illness and related factors, the majority of eligible patients approached to enter the study did so, and the pain scoring was well tolerated. The implications of this for future research and clinical practice are discussed. In 6 patients only 1 pain mechanism was identified (visceral 4, deep somatic 2). Two mechanisms were present in 8 patients and 3 mechanisms in 6 patients. The deep somatic mechanism was identified in 15 patients, visceral mechanism in 13, neurogenic in 10 and superficial somatic in 2. The most common combination of mechanisms was neurogenic/visceral/deep somatic (5 patients) and neurogenic/deep somatic (4 patients). No patient had neurogenic pain alone or superficial pain alone. To achieve optimal analgesia, a mean of 2.8 drug classes per patient was required (range: 1-5). All 20 patients required an opioid, and in 2 patients with visceral pain only, morphine was the initial and sole analgesic used. None of the 15 patients with deep somatic pain achieved acceptable pain relief with an anti-inflammatory drug alone at conventional dose levels. It is concluded that the approach is feasible, and prospective assessment and validation of the response of these proposed mechanism categories to specific drug classes is now underway. Assessment of the anti-inflammatory responsive component of nociceptive cancer pain has emerged as a priority for further investigation.