Abnormal low frequency drive in myoclonus-dystonia patients correlates with presence of dystonia.

The pathophysiology of Myoclonus-Dystonia (M-D), an autosomal dominantly inherited movement disorder is largely unknown. In different forms of dystonia abnormal intermuscular coherence is present. The objective of this study was to investigate whether the myoclonic and dystonic features are the result of an abnormal common drive to the muscles in M-D. Coherence analysis was performed in 20 DYT11 mutation carriers (MC) and 13 healthy controls during resting condition and during weak isometric contraction of the arm and neck. The EMG-EMG coherence analysis showed significantly increased intermuscular 3 to 10 Hz coherence in 4 DYT11 MC with clinical pronounced (mobile and static) dystonia. This coherence was not present in DYT11 MC with mild (static) dystonia and/or predominating myoclonus. The EEG-EMG analysis showed significant 15 to 30 Hz coherence during weak isometric contraction of the arm in five healthy controls, but in none of the DYT11 MC. The intermuscular coherence in the low frequency band in DYT11 MC with predominant dystonia is concordant with the previously described coherence in dystonia and suggests that the pathophysiology of M-D shares common pathophysiological features with dystonia. The absence of 15 to 30 Hz EEG-EMG coherence in DYT11 MC may reflect abnormal motor activation caused by an altered cortical drive because of the basal ganglia dysfunction.