Abstracts

Rationale: Historically the presence of classical triphasic morphology waveforms (TMWs) on the EEG has been considered to indicate a metabolic or toxic cause of cerebral dysfunction compatible with a diffuse encephalopathy. TMWs at times can also be seen in patients with seizures. In patients presenting with altered sensorium or history of seizures, their presence may raise concern for non-convulsive seizures (NCS).Methods: We decided to look at all sequential EEG studies referred to our laboratory for the presence of TMWs over a 12-month period (June 2010-May 2011). This comprised studies on outpatients as well as portable EEG studies requested on patients admitted to the hospital. Our intention was to correlate their presence with the patient s diagnosis, outcome (30-day mortality) and presence of seizures. We categorized the TMWs into a) typical TMWs (defined as generalized, bilateral synchronous, bifrontally predominant positive sharp transients of high amplitude that are preceded and followed by negative waves of relatively lower amplitude) and b) TMWs with additional features (atypical morphology or/and periodicity in a background of diffuse slowing). For the TMWs with additional features we identified the patients that had further continuous EEG monitoring.Results: We reviewed 1459 records and we identified 71 records (62 patients) with TMWs on routine/portable EEG. Of those, 36 records had typical TMWs and 35 records had TMWs with additional features. For the first category, the most common diagnosis was sepsis and the 30-day mortality rate was less than 10%. In this group only two patients had continuous EEG monitoring and there were no seizures recorded. For the second category, the most common diagnosis was multifactorial (sepsis, renal failure, hypoxia) and the 30-day mortality rate was 37%. In this group, sixteen patients had continuous EEG monitoring and three were found to have non-convulsive seizures (NCS).Conclusions: We conclude that the most common cause of typical TMWs was sepsis and their presence is compatible with a favorable prognosis. The TMWs with additional features were commonly seen in patients with multifactorial causes, their presence signifies a high mortality rate and patients should be closely monitored for the presence of NCS. In selected group of these patients, continuous EEG monitoring may yield additional information.