Changes in central opioid receptor binding in relation to inflammation and pain in patients with rheumatoid arthritis.

A group of four patients with RA were examined to test the hypothesis that there is a change in the endogenous opioid system in the brain during inflammatory pain. Regional cerebral opioid receptor binding was quantified using the opioid receptor antagonist [11C] diprenorphine and positron emission tomography (PET). In the four patients studied in and out of pain, significant increases in [11C]diprenorphine binding were seen in association with a reduction in pain. Increases were seen in most of the areas of the brain that were sampled apart from the occipital cortex. Significant region-specific increases over and above the more generalized changes were also seen in the frontal, cingulate and temporal cortices in addition to the straight gyrus. These findings are consistent with the hypothesis that there are substantial increases in occupancy by endogenous opioid peptides during inflammatory pain.