Pain characterization in cancer patients and the analgetic response to epidural morphine

In 48 patients with pain related to malignancy, a pain characterization was performed during oral opioid therapy. After an optimal epidural morphine regimen had been established, the alteration in pain relief was evaluated by means of a visual analogue scale. The CSF and plasma morphine concentrations at minimum steady state were then analysed in 28 patients and related to the degree of pain relief. The efficacy of the spinal treatment ranked in the following order: somatic greater than visceral greater than radiating = 0, but the difference was only significant between the somatic and radiating pain groups. There was a tendency for continuous pain to be better relieved than intermittent pain. No correlations were found between the CSF or plasma morphine concentrations and the degree of pain relief, suggesting that not all pain impulses are modulated in a dose-dependent manner by morphine at the spinal level. Pain characterization may be instrumental in providing an optimal spinal opioid analgesia in malignancy. Moreover, there is a need for better defined diagnostic criteria for clinical pain characterization.