Pathophysiology of unilateral asterixis due to thalamic lesion.

OBJECTIVE Unilateral asterixis has been reported in patients with thalamic lesion. This study aims at elucidating the pathophysiology of the thalamic asterixis. METHODS Two cases with unilateral asterixis caused by an infarction in the lateral thalamus were studied by analysing the asterixis-related cortical activities, transcranial magnetic stimulation (TMS) for motor cortex excitability and probabilistic diffusion tractography for the thalamo-cortical connectivity. RESULTS Averaging of electroencephalogram (EEG) time-locked to the asterixis revealed rhythmic oscillations of a beta band at the central area contralateral to the affected hand. TMS revealed a decrease in the motor evoked potential (MEP) amplitude and a prolongation of the silent period (SP). The anatomical mapping of connections between the thalamus and cortical areas using a diffusion-weighted image (DWI) showed that the lateral thalamus involved by the infarction was connected to the premotor cortex, the primary motor cortex (M1) and the primary somatosensory cortex (S1) of the corresponding hemisphere. CONCLUSIONS The thalamic asterixis is mediated by the sensorimotor cortex, which is subjected to excessive inhibition as a result of the thalamic lesion involving the ventral lateral nucleus. SIGNIFICANCE This is the first demonstration of participation of the sensorimotor cortex in the generation of asterixis due to the lateral thalamic lesion.