Brain biomarkers for CRPS.

For complex regional pain syndrome (CRPS), a number of brain biomarkers have been identified which show overlaps but also unique characteristics to other chronic pain syndromes. We here provide a review about possible brain biomarkers for CRPS and differentiate their role for A) diagnosis of CRPS, B) monitoring of time course of CRPS (e.g., during interventions) or C) outcome prediction and treatment stratification. In addition, the transition from the sub-chronic to the chronic phase is extremely important to investigate the development of a chronic pain syndrome. The use of these biomarkers might help to stratify patients individually for most effective interventions. Our approach involved screening of existing imaging literature on CRPS patients to identify alterations in the gray matter volume (GMV) of the brain, structural (diffusion tensor imaging) and functional connectivity (rsFMRI), and task-specific brain activity (response to sensory/painful stimuli, motor tasks, imagery). Furthermore, we will provide an overview of cortical excitability and neurotransmitter balance alterations in CRPS.