Muscle hyperalgesia is widespread in patients with complex regional pain syndrome

Patients with complex regional pain syndrome (CRPS) frequently show prominent sensory abnormalities in their affected limb, which may extend proximally and even to unaffected body regions. This study examines whether sensory dysfunction is observed in unaffected body parts of CRPS patients, and investigates whether the extent of dysfunction is similar for the various sensory modalities. Quantitative sensory testing was performed in the unaffected extremities and cheeks of 48 patients with CRPS of the arm (31 with dystonia), and the results were compared with values obtained among healthy controls. The most prominent abnormality was the pressure pain threshold, which showed a consistent pattern of higher sensitivity in unaffected contralateral arms and unaffected legs, as well as the cheek, and demonstrated the largest effect sizes. The cheeks of CRPS patients showed thermal hypoesthesia and hyperalgesia as well as a loss of vibration detection. Except for a lower vibration threshold in the contralateral leg of CRPS patients with dystonia, no differences in sensory modalities were found between CRPS patients with and without dystonia. These results point to a general disturbance in central pain processing in patients with CRPS, which may be attributed to impaired endogenous pain control. Since pressure pain is the most deviant sensory abnormality in both unaffected and affected body regions of CRPS patients, this test may serve as an important outcome parameter in future studies and may be used as a tool to monitor the course of the disease.