The aim of the present study has been to assess the responsiveness of various types of
chronic pain to
opioids given i.v. and tested against placebo in a double-blind, randomized fashion.
Pain classified as primary nociceptive was effectively alleviated (P greater than 0.001) while neuropathic
deafferentation pain was not significantly influenced by
morphine or equivalent doses of other
opioids. Also 'idiopathic'
pain, defined as
chronic pain with no or little demonstrable pathology, failed to respond. The results were not related to whether the patients were regular users of
narcotic analgesics or not. The outcome of our double-blind
opioid test has proved useful to justify a continued, or discontinued, use of
narcotic medication in individual patients. It may also support the indication and choice of invasive stimulation procedures (spinal cord or brain). The results of the study illustrate the misconception of
chronic pain as an entity and highlight the importance of recognizing different neurobiological mechanisms and differences in responsiveness to
analgesic drugs as well as to non-pharmacological modes of treatment. The
opioid test has thus become a valuable tool in
pain analysis and helpful as a guide for further treatment.