Involvement of Primary Motor Cortex in Wilson's Disease Postural Tremor

Objective: The following study included five Wilson's disease (WD) patients showing a right-sided postural forearm tremor (4 6Hz) and addressed the question whether the primary motor cortex (M1) is directly involved in the generation of tremor. Methods: Using a 122-channel whole-head neuromagnetometer and surface EMGs we investigated cerebro-muscular coupling. Postural tremor was observed in a sustained 45° posture of the right-sided forearm. Data were analyzed using Dynamic Imaging of Coherent Sources (DICS), revealing cerebro-muscular coupling between EMG and cerebral activity. Coherent sources were superimposed on individual high-resolution T₁-weighted MR images. Phase lags between EMG and cerebral areas showing the strongest coherence were determined by means of a Hilbert transform of both signals. Results: In all patients postural tremor was associated with strong coherence between tremor EMG and activity in the contralateral primary sensorimotor cortex (S1/M1) at tremor or double tremor frequency. Phase lag values between S1/M1 activity and EMG revealed efferent and afferent components in the cortico-muscular coupling. Conclusions: Taken together our results indicate that postural tremor in Wilson's disease is mediated through a pathological oscillatory drive from the primary motor cortex.