Asterixis

Asterixis (Greek a, not + stērixis, fixed position) is a flapping tremor of the wrist upon extension (dorsiflexion), sometimes said to resemble a bird flapping its wings. Also called liver flap, it can be a sign of hepatic encephalopathy (damage to brain cells due to the inability of the liver to metabolize ammonia to urea). The exact cause is not known, but it is thought to be related to abnormal ammonia metabolism.

Adams and Foley first described asterixis in 1949 in patients with severe liver failure and encephalopathy. In general, there are brief, arrhythmic interruptions of sustained voluntary muscle contraction causing brief lapses of posture, with a frequency of 3-5 Hz. It is bilateral, but may be asymmetrical. Asterixis is seen most often in drowsy or stuporous patients with metabolic encephalopathies, especially in decompensated cirrhosis or acute hepatic failure. It is also seen in some patients with renal failure and azotemia, and in carbon dioxide toxicity. Asterixis can also be a feature of Wilson's disease.