Fine-grained mapping of cortical somatotopies in chronic Complex Regional Pain Syndrome

Abstract It has long been thought that severe chronic pain conditions, such as Complex Regional Pain Syndrome (CRPS), are not only associated with, but even maintained by a reorganisation of the somatotopic representation of the affected limb in primary somatosensory cortex (S1). This notion has driven treatments that aim to restore S1 representations, such as sensory discrimination training and mirror therapy. However, this notion is based on both indirect and incomplete evidence obtained with imaging methods with low spatial resolution. Here, we used functional MRI to characterize the S1 representation of the affected and unaffected hand in patients with unilateral CRPS. At the group level, the cortical area, location, and geometry of the S1 representation of the CRPS hand were largely comparable to those of the healthy hand and controls. However, the area of the map of the affected hand was modulated by disease duration (the smaller the map, the more chronic the CRPS), but not by pain intensity, pain sensitivity and severity of the physical disability. Thus, if any map reorganization occurs, it does not appear to be directly related to our pain measures. These findings compel us to reconsider the cortical mechanisms underlying CRPS and the rationale for interventions that aim to “restore” somatotopic representations to treat pain. Significance statement This study shows that the spatial map of the fingers in S1 is largely preserved in chronic CRPS. Shrinkage of the area of the affected hand map can occur in the most chronic stages of disease. Map shrinkage is related to CRPS duration rather than diagnosis, and is unrelated to how much pain patients experience or to the severity of the physical disability. These findings challenge the rationale for using sensory interventions to treat pain by restoring somatotopic representations in CRPS patients.