Brain Advance Access originally published online on August 18, 2009
Brain 2009 132(10):2871-2877; doi:10.1093/brain/awp213
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Abnormal sensorimotor plasticity in organic but not in psychogenic dystonia
1 Department of Neurosciences, Psychiatry and Anaesthesiology, University of Messina, Italy 2 Department of Neurology, NYU School of Medicine, New York, NY, USA 3 Sobell Department of Motor Neuroscience, Institute of Neurology, University College London, London, UK
Correspondence to: Dr Angelo Quartarone, Clinica Neurologica 2, Policlinico Universitario, 98125 Messina, Italy E-mail: angelo.quartarone{at}unime.it
Dystonia is characterized by two main pathophysiological abnormalities: ‘reduced’ excitability of inhibitory systems at many levels of the sensorimotor system, and ‘increased’ plasticity of neural connections in sensorimotor circuits at a brainstem and spinal level. A surprising finding in two recent papers has been the fact that abnormalities of inhibition similar to those in organic dystonia are also seen in patients who have psychogenic dystonia. To try to determine the critical feature that might separate organic and psychogenic conditions, we investigated cortical plasticity in a group of 10 patients with psychogenic dystonia and compared the results with those obtained in a matched group of 10 patients with organic dystonia and 10 healthy individuals. We confirmed the presence of abnormal motor cortical inhibition (short-interval intracortical inhibition) in both organic and psychogenic groups. However, we found that plasticity (paired associative stimulation) was abnormally high only in the organic group, while there was no difference between the plasticity measured in psychogenic patients and healthy controls. We conclude that abnormal plasticity is a hallmark of organic dystonia; furthermore it is not a consequence of reduced inhibition since the latter is seen in psychogenic patients who have normal plasticity.
Key Words: associative plasticity; organic dystonia; psychogenic dystonia; paired associative stimulation; transcranial magnetic stimulation
Abbreviations: AMT, active motor threshold; ANOVA, analysis of variance; APB, abductor pollicis brevis; FDI, first dorsal interosseus; LAI, long afferent inhibition; LICI, long interval intracortical inhibition; MEP, motor evoked potential; PAS, paired associative stimulation; RMT, resting motor threshold; SAI, short afferent inhibition; SICI, short interval intracortical inhibition; TMS, transcranial magnetic stimulation
Received March 18, 2009. Revised May 22, 2009. Accepted June 30, 2009.