Motor cortex dysfunction in complex regional pain syndrome

Objective: Most patients with complex regional pain syndrome (CRPS) exhibit debilitating motor symptoms. The effect of continuous pain on motor system in CRPS, however, is not well known. We searched for signs of motor cortex dysfunction in chronic CRPS type 1 patients with motor impairment. Methods: We recorded rhythmic brain activity with magnetoencephalography (MEG) during noxious thulium-laser stimulation of both hands in eight CRPS patients and eight control subjects. We measured excitability of the motor cortex by monitoring the reactivity of the similar to 20-Hz motor cortex rhythm to laser stimuli. The reactivity was defined as a sum of the stimulus-induced suppression and the subsequent rebound of the similar to 20-Hz rhythm. Results: In CRPS, the reactivity of the similar to 20-Hz rhythm in the hemisphere contralateral to the painful hand was significantly weaker than in control subjects. The reactivity correlated with the mean level of the spontaneous pain (r = -0.64, P = 0.04). Suppression of the similar to 20-Hz rhythm correlated with the grip strength in the painful hand (r = 0.66, P = 0.04). Conclusion: Continuous pain in CRPS is associated with attenuated motor cortex reactivity. Significance: Abnormal motor cortex reactivity may be linked with motor dysfunction of the affected hand in CRPS. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.