Central poststroke pain and reduced opioid receptor binding within pain processing circuitries: a [11C]diprenorphine PET study.

Based on concepts that endogenous opioids participate in neural transmission of pain, the present study in central poststroke pain (CPSP) patients investigated changes in opioid receptor (OR) binding in neural structures centrally involved in the processing of pain. Five patients with central pain after lesions in the brain stem, thalamus or parietal cortex and twelve healthy volunteers underwent a [11C]diprenorphine positron emission tomography study. Binding potentials were calculated using a reference region model in all subjects. Statistical parametric mapping was applied for t-statistical analysis on voxel-basis. Binding potential values for each individual were extracted from a volume of interest at each identified significant peak. Spectral analysis was applied for quantification of global values. Significant regional reduced 11C-diprenorphine binding (corrected for multiple tests) was detected in contralateral thalamus, parietal, secondary somatosensory, insular and lateral prefrontal cortices, and along the midline in anterior cingulate, posterior cingulate and midbrain gray matter. Individual extracted binding values disclosed a reduced binding in these regions in all patients independent from the particular lesion site. The poststroke pain syndrome is associated with a characteristic pattern of reduced OR binding within the neural circuitry processing pain. It is suggested that an imbalance of excitatory-inhibitory mechanisms in certain brain structures, as evidenced in decreased [11C]diprenorphine binding, is one of the causes or the consequences of poststroke pain.