RESUMO
Valproate is a widely used antiepileptic drug with rarely occurring serious side effects. However, valproate may induce hyperammonemic encephalopathy. A 85-year-old woman was admitted with stuporous mental status. Brain MRI showed old cerebral infarction and EEG showed sharp waves in the right frontal region. Under the impression of postictal confusion, we used phenytoin and then she was improved. However, the intermittent vacant staring was seen, and valproate was administered additionally. On the 5th day after adding valproate, her mentality was deteriorated and intermittent triphasic waves appeared on EEG. Due to confused mentality and hyperactivities, we injected lorazepam and then semicomatous mentality was developed. Follow-up EEG showed nearly continuous triphasic waves and slightly elevated ammonia with normal liver function was shown. After stopping antiepileptic drugs, we used lactulose and flumazenil, and then she was fully recovered with normalized EEG. This is a rare case of valproate-induced hyperammonemic encephalopathy with triphasic waves.