Background: The number of neuroimaging studies that examine chronic pain are relatively small, and it is clear that different chronic pain conditions activate diverse regions of the brain.
Objective: Cancer patients presenting for diagnostic positron emission tomography (PET) imaging were asked to rate their spontaneous baseline pain score. Twenty patients with either no pain (NRS = 0) or with moderate to severe pain (NRS = 4) were invited to participate in this study to determine the difference in brain activity in cancer patients with moderate to severe chronic pain versus no pain.
Study design: Prospective, non-randomized, observational report.
Setting: Academic medical center.
Methods: Patients had a 2-D PET scan with the radionuclide 18F-fluoro-2-deoxyglucose (FDG) at a dose of approximately 20 mCi. Each individual raw PET scan was coregistered and normalized to standard stereotactic space. Differences in regional glucose metabolism were then statistically compared between patients with moderate-to-severe pain and patients with no pain.
Results: The NRS pain score in the patients with moderate to severe pain (n = 11) was 4.5 [4.0-6.0] (median [interquartile range]) versus 0.0 [0.0-0.0] (p < 0.001) in the group with no pain (n = 9). Compared to patients with no pain, patients with moderate to severe pain had increased glucose metabolism bilaterally in the prefrontal cortex, BA 9-11. Unilateral activation was found in the right parietal precuneus cortex, BA 7. There were no areas of the brain in which there was decreased activity due to moderate to severe pain.
Conclusions: Our results showing a preferential activation of the prefrontal cortex are consistent with results from studies showing that affective pain perception and negative emotions play an important part in the chronic pain experience.
Limitations: This was not a randomized clinical trial. Patient medication was not controlled.