A disturbance in sensory processing on the affected side of the body increases limb pain in complex regional pain syndrome.

OBJECTIVES The aim of this study was to determine whether a central disturbance in somatosensory processing contributes to limb pain in complex regional pain syndrome (CRPS). METHODS In 37 patients with CRPS, the effect of cooling the ipsilateral forehead on pain in the affected limb was compared with the effect of cooling the contralateral forehead. In addition, symptoms associated with cold-evoked limb pain were explored. RESULTS Limb pain generally increased when the ipsilateral side of the forehead was cooled but did not change when the contralateral side of the forehead was cooled. Increases were greatest in patients with heightened sensitivity to cold, brushing, and pressure-pain in the ipsilateral forehead, in patients with heightened sensitivity to pressure-pain in the limbs, and in patients with chronic symptoms. In contrast, sensitivity to light touch was diminished in the CRPS-affected limb of patients whose limb pain remained unchanged or decreased during ipsilateral forehead cooling. CONCLUSIONS These preliminary findings suggest that a central disturbance in sensory processing and pain modulation, which extends beyond the affected limb to the ipsilateral forehead, contributes to symptoms in a subgroup of patients with CRPS.