King's College London

Objective
Sensorimotor processing is abnormal in Idiopathic/Genetic dystonias, but poorly studied in Acquired dystonias.  Beta-Corticomuscular coherence (CMC) quantifies coupling between oscillatory electroencephalogram (EEG) and electromyogram (EMG) activity and is modulated by sensory stimuli.  We test the hypothesis that sensory modulation of CMC and intermuscular coherence (IMC) is abnormal in Idiopathic/Genetic and Acquired dystonias.
Methods
Participants: 11 children with Acquired dystonia, 5 with Idiopathic/Genetic dystonia, 13 controls (12-18years).  CMC and IMC were recorded during a grasp task, with mechanical perturbations provided by an electromechanical tapper.  Coherence patterns pre- and post-stimulus were compared across groups.
Results
Beta-CMC increased post-stimulus in Controls and Acquired dystonia (p=0.001 and p=0.010, respectively), but not in Idiopathic/Genetic dystonia (p=0.799).  The modulation differed between groups, being larger in both Controls and Acquired dystonia compared with Idiopathic/Genetic dystonia (p=0.003 and p=0.022). Beta-IMC increased significantly post-stimulus in Controls (p=0.004), but not in dystonia.  Prominent 4-12Hz IMC was seen in all dystonia patients and correlated with severity (rho=0.618). 
Conclusion
Idiopathic/Genetic and Acquired dystonia share an abnormal low-frequency IMC.  In contrast, sensory modulation of beta-CMC differed between the two groups.
Significance
The findings suggest that sensorimotor processing is abnormal in Acquired as well as Idiopathic/Genetic dystonia, but that the nature of the abnormality differs.