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Nonconvulsive status epilepticus (NCSE) is often diagnosed based on abolition of rhythmic sharp waves by benzodiazepines. It is possible that sharp waves resulting from metabolic (nonepileptic) encephalopathies may also respond to benzodiazepines and are potentially misdiagnosed as NCSE. The authors hypothesized that triphasic waves (TW) resulting from metabolic encephalopathy are abolished by benzodiazepines. They retrospectively identified patients with TW resulting from metabolic encephalopathy who had EEG recordings before, during, and after benzodiazepine administration. Benzodiazepines were given either because of the possibility of NCSE or for a medically indicated purpose. All patients were diagnosed definitively with a metabolic cause of encephalopathy and not NCSE. Ten patients (mean age, 59 years) met the criteria and were reviewed. TW resolved persistently in four patients and intermittently in six patients. Background activity slowed in five patients and was attenuated in five patients. Unresponsive patients did not arouse and three of five drowsy patients became less responsive. Rhythmic sharp waves resulting from metabolic encephalopathy are abolished by benzodiazepines, similar to NCSE, but without improvement in mental status. This suggests that definitive electrographic diagnosis of primary NCSE should not be based entirely on abolition of sharp waves by benzodiazepines. This also implies that gamma-aminobutyric acid neurotransmission is important in the expression of TW.