EEG Triphasic Waves

Triphasic waves are abnormal electroencephalogram (EEG) waveforms seen in association with multiple clinical conditions, including encephalopathy and structural brain lesions, among others. They are nonspecific, high amplitude sharp/sharply contoured waves with three distinctive phases. The main phase is surface positive with a high amplitude (greater than 70 microvolts), preceded by a low amplitude negative deflection and followed by a slow rising broad negative deflection. They were initially believed to be pathognomonic of hepatic encephalopathy; however, they can be seen in any metabolic encephalopathy (in fact, more common with renal than hepatic conditions) and some other conditions. They may be considered a subset of generalized periodic discharges (GPDs).

This EEG pattern was first described by Foley in 1950. It was an EEG recording of a patient with hepatic encephalopathy. The author described the waveforms as "blunted and spike waves." There is an abundance of literature in the 1950s on this topic, and most of the literature then suggested this finding to be specific to hepatic encephalopathy. It was felt to represent high mortality with severe liver conditions like portal cirrhosis, metastatic liver disease, infective hepatitis, etc. At that time, EEG was used to diagnose early stages of hepatic encephalopathy and as a tool to guide treatment with medications like neomycin. The term triphasic waves was first coined in 1955 by Bickford and Butt, given the three-phase morphology.