Functional Imaging in Complex-Regional Pain Syndromes

Complex-regional pain syndromes (CRPS) are distressing neuropathic pain syndromes, mainly resulting from injury at the extremities. The clinical triad comprises sensory, motor and autonomic disturbances. Pain and hyperalgesia are hallmarks of this syndrome. Patterns of sensory and motor symptoms may indicate that the pathophysiology of CRPS is not only limited to the affected limb, but also includes changes in the central nervous system (CNS). Therefore, we employed functional imaging techniques in CRPS patients in order to explore potential CNS changes in more detail. In a first study we investigated the somatotopic organization within the primary somatosensory cortex (S1) in acute forms of CRPS by means of magnetoencephalography (MEG). We found a significant shrinkage of the corresponding cortical hand field contralateral to the CRPS affected side. The hand position was switched to a more lateral and inferior position towards the lip. Predictors for these plastic changes were overall pain and the extension of mechanical hyperalgesia. In a second MEG follow-up study (at least one year of follow-up) we could demonstrate that cortical reorganization reversed following successful treatment of CRPS. The recovery from neuropathic pain symptoms predicted recovery from cortical reorganization. Therefore, we could demonstrate a link between central nociceptive sensitization and cortical plasticity. In a third study we used functional magnetic resonance imaging (fMRI) in order to delineate the neuronal matrix of touch-evoked pain (i.e., dynamic-mechanical allodynia) in CRPS. Our results suggest the recruitment of a complex brain network underlying allodynia in CRPS. The most important cortical areas identified within this network were secondary somatosensory cortices, insula, prefrontal cortices, parietal cortices and the cingulate cortex. In summary, the presented studies provide further evidence for an involvement of the CNS in the pathophysiology of CRPS. Supported by the German Research Network „Neuropathic Pain Syndromes“ of the German Federal Ministry of Education and Research (BMBF).