Unexplained encephalopathy with phenytoin toxicity - hyperammonemia, the underlying cause

[...]he was diagnosed as a case of phenytoin toxicity with phenytoin-induced hyperammonemic encephalopathy. [...]a very high plasma ammonia level, in contrast to the mildly raised plasma phenytoin level suggested hyperammonemia, which was the cause of encephalopathy. [...]we conclude that unexplained acute onset encephalopathy in a setting of suspected phenytoin toxicity could be due to hyperammonemia seen on phenytoin monotherapy.