Asterixis is a sudden, brief, arrhythmic lapse of sustained posture due to involuntary interruption in muscle contraction. It is most easily demonstrated by observing the dorsiflexed hands with arms outstretched (i.e., the motion to indicate "stop"), lapses being seen as flicking or flapping movements of the hands ("flapping tremor").
Movement is associated with EMG silence in antigravity muscles for 35-200 ms. These features distinguish asterixis from tremor and myoClonus; the phenomenon has previously been described as negative myoclonus or negative tremor.
Asterixis may be bilateral or unilateral. Recognized causes of asterixis include:

Hepatic encephalopathy Hypercapnia
Drug-induced, for example, anticonvulsants, levodopa
Structural brain lesions: thalamic lesions (hemorrhage, thalamotomy)

Unilateral asterixis has been described in the context of stroke, contralateral to lesions of the midbrain (involving corticospinal fibers, medial lemniscus), thalamus (ventroposterolateral nucleus), primary motor cortex and parietal lobe; and ipsilateral to lesions of the pons or medulla.



Marchini M, Sayegh GA, Caudana R. Unilateral asterixis and stroke in 13 patients: localization of the lesions matching the CT scan images to an atlas. European Journal of Neurology 2004; 11(suppl2): 56 (abstract P1071)

Cross References

Encephalopathy; Myoclonus; Tremor