Central opioidergic neurotransmission in complex regional pain syndrome

Objectives Peripheral as well as central mechanisms are thought to contribute to the pathogenesis of complex regional pain syndrome (CRPS). Opioidergic drugs are barely effective in CRPS, therefore we investigated the cortical opioid receptor status in CRPS patients.

Methods Ten CRPS patients underwent a PET scan with the opioidergic radioligand [F-18]fluoroethyl-diprenorphine. The pain status was assessed with the McGill pain questionnaire, the Hospital Anxiety and Depression Scale (HADS) was assessed additionally. The binding potential (BP) was computed voxelwise by means of the modified Logan Plot. SPM 2 was used.

Results Categorical comparisons revealed significant (p<0.001, corrected) reduced BP in patients in the amygdala and parahippocampal cortex contralateral to the painful limb. Significant increased BP was found in the contralateral ventromedial prefrontal cortex and the contralateral middle frontal gyrus.A significant negative correlation between McGill PRI scores and the BP in the midcingulate cortex and the ipsilateral middle temporal gyrus was found.The magnitude of anxiety correlated positively with BP in contralateral medial temporal regions, a significant negative correlation could be shown with BP in the contralateral parahippocampal cortex. The scores in the depression subscale of the HADS were positively correlated to the opioid receptor availability in the contralateral superior temporal cortex.

Conclusions Our results reveal a reduced opioid receptor availability in structures involved in nociception and pain processing in CRPS.Higher pain levels, anxiety and depression correlated with opioid receptor availability in areas, which are related to the affective-motivational component of pain.