Objectives
Abnormal sensorimotor processing is present in adult genetic dystonia, but is sparsely studied in acquired or childhood dystonia.  This study investigates sensorimotor processing by measuring event-related synchronisation (ERS) and desynchronization (ERD) in response to a proprioceptive stimulus in children with dystonia/dystonic cerebral palsy (CP).

Methods
30 young people with dystonia (20 genetic/idiopathic; 10 dystonic CP) and 22 controls participated, age 5-21years.  Proprioceptive stimuli, comprising a brief stretch of the wrist flexors, were delivered to each hand using a robotic wrist interface, (for 5 patients, dominant hand only was tested). Scalp EEG was recorded, filtered (DC-500Hz) and sampled at 2500Hz.   Wrist position was monitored and movement onset synchronised with EEG recordings. Up to 160 EEG epochs (1s pre- and 3.5s post-stimulus) were averaged per subject to produce a Stretch Evoked Potential. Time-frequency analyses were performed using continuous Morlet wavelet transforms to compute power in 1Hz bins between 5-40Hz, using 8 wavelet cycles. The relative change in post-stimulus power with respect to pre-stimulus/baseline, was calculated for the alpha/mu (8-12Hz) band for each time point.

Results
Mean age was 12.7years and was comparable across groups. Controls showed a clear developmental profile in event-related spectral changes. Findings were compared between control and dystonia groups using age as a covariate.  Controls showed a prominent early alpha/mu ERD (0.5-1s post-stimulus) and a prominent alpha/mu ERS (1.5–2.5s post-stimulus) over contralateral sensorimotor cortex following movement of either hand. Alpha ERD was significantly smaller in the dystonia group for both the dominant hand (ANCOVA F(2,47)=4.45 p=0.017) and the non-dominant hand (ANCOVA F(2,42)=9.397 p<0.001). Alpha ERS was significantly smaller in dystonia for the dominant hand (ANCOVA F(1,48)=13.132 p=0.001).  The findings were similar for genetic/idiopathic dystonia and dystonic CP.

Conclusions
The impaired alpha/mu modulation indicates a developmental abnormality of sensorimotor processing which is common to genetic/idiopathic dystonia and dystonic CP.