A Randomized Trial of Patients With Complex Regional Pain Syndrome Comparing Graded Motor Imagery and Desensitization Versus Simple Desensitization and Changes in Resting-State Connectivity of Cerebral Networks Before and After Treatment.

CRPS: Complex regional pain syndrome (CRPS) is characterized by severe and disabling pain typically in a limb in combination with sensory, autonomic, trophic, and motor abnormalities like tremor and dystonia. A distinction is made between CRPS-1, usually following an injury (fracture, surgery) without a nerve lesion, and CRPS-2, in which a distinct nerve lesion can be identified.

Brain mapping studies have provided increasing evidence that the central nervous system is playing an important role in the pathogenesis of CRPS. Reorganization of the somatosensory cortex and motor networks, with altered central processing of tactile and nociceptive stimuli as well as movement control has been demonstrated.

Functional brain imaging studies suggest that the volume of brain activation differs between motor execution and motor imagery, but the distribution of cerebral activity tends to be similar. Under imaginary movement of affected hands Gieteling et al. (2008) observed that there was reduced activation ipsilaterally in the premotor and adjacent prefrontal cortex, frontal operculum, anterior part of the insula cortex, and the superior temporal gyrus.

Stimulus-driven, functional magnetic resonance imaging, however, are time-consuming and prone to possible confounds, especially in clinical populations. In that perspective resting-state functional magnetic resonance imaging (RS-fMRI), measuring the cerebral networks at rest (in absence of any task), is probably better suited to clinical examinations and is widely used to investigate brain networks that exhibit correlated fluctuations. During recent years, a large number of studies have indicated that RS-fMRI is sufficiently constrained by anatomy to allow the architecture of distinct brain systems to be characterized.

The default mode network (DMN) is probably the most studied resting state network. It seems to be involved in several processes and is found negatively modulated by chronic pain. Only one published study has investigated cerebral networks and cerebral connectivity in CRPS. Here the default mode network displayed reduced connectivity with the S1 compared to healthy controls. This indicates that decreased connectivity may be a key feature in cerebral functioning of CRPS patients. No study, however, has so far investigated if the reduced connectivity in the DMN is reversed in CRPS patients who experience pain reduction after GMI or desensitization treatment.