![]() Triphasic waves (TW) consist of moderate to high amplitude complexes with three (but sometimes two or four) negative-positive-negative phases, usually occurring in runs at 1.5–3 per second. Metabolic encephalopathiesĪ patient with acute change in awareness whose EEG shows triphasic waves and diffuse slow activity will usually have a metabolic encephalopathy. None of these patterns is specific to a particular pathophysiological process or diagnosis, but PEDs are most likely to occur in acute or subacute focal destructive pathologies or focal epileptogenic lesions triphasic waves are typically found in metabolic encephalopathies and some patients with mesial fronto-parietal lesions or third ventricle tumours show FIRDA in their EEG. A variety of additional EEG patterns can be seen, such as frontal intermittent rhythmic delta (FIRDA), periodic lateralised or bilateral epileptiform discharges (PEDs, BIPEDs), and triphasic waves. In mild encephalopathic states, slowing of normal alpha (α) rhythms occurs, and with more severe encephalopathy, the appearance of theta (θ) and continuous or non-continuous delta (δ) activities. There is a progressive increase in slow wave activities, the degree of which parallels the severity of brain dysfunction. EEG changes in encephalopathies are similar, whether the cause is septic, metabolic, toxic, or structural. ![]()
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