Phenytoin-induced asterixis--uncommon or under-diagnozed?

Asterixis is a recognized but uncommon clinical sign of phenytoin toxicity. A case is presented in which asterixis and acute cerebellar dysfunction occurred when the phenytoin levels reached the toxic range. It disappeared when the drug levels normalized. Asterixis is now classified as a form of negative myoclonus, which is characterized by irregular myoclonic lapses of posture. The neurochemistry and physiology of phenytoin causing asterixis has yet to be elucidated.