Midbrain asterixis.

Asterixis is usually a manifestation of metabolic encephalopathy. It was the only skeletal motor sign in a patient with ophthalmoplegia caused by midbrain infarction; no metabolic abnormality was present. The asterixis was accompanied by signs of damage to the mesencephalic reticular formation. We propose that episodic lapses of postural control by the reticular formation are responsible for midbrain asterixis and suggest that this asterixis is a segmental form of drop attack.