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<embedvideo service="youtube" Alignment="right">https://youtu.be/L92A-QbN0Kw</embedvideo>Seen primarily in metabolic encephalopathy, particularly hepatic and renal encephalopathy, asterixis is an inability to sustain normal muscle tone .(1-3). With the arms outstretched and wrists extended, “like stopping traffic,” the lapse in postural tone may cause the hands to suddenly flop downward, then quickly recover, causing a slow and irregular flapping motion that led to the term “liver flap.” (Video) When severe, the entire arm may drop. Other body parts may exhibit the phenomenon (e.g., inability to keep the foot dorsiflexed [foot flap]).
In unresponsive patients, asterixis at the hip joints can sometimes be brought out by passively flexing and abducting the hips and placing the feet together so that the thighs form a “V.” In this position, the periodic loss of adductor tone may cause the knees to flap up and down. (4)
Asterixis is usually bilateral. Unilateral asterixis may occur with focal brain lesions. The most common structural cause of asterixis is ischemia or hemorrhage in the CNS; most frequently involving the genu and anterior portion of the internal capsule or ventrolateral thalamus.
In a study of 45 patients with structural cerebral pathology, asterixis was unilateral in 37 and bilateral in eight. (5)
In a study of 103 patients, asterixis was bilateral in 79 cases (81.4%) and unilateral in 18 (18.6%).(6) In some cases, it was easier to elicit in the upper extremities, in others it was easier to elicit in the lower limbs. Causes included medications, renal disorder, hepatic dysfunction, pulmonary insufficiency, stroke and other brain lesions (malignancy, subdural hematoma and epidural abscess).
