Abstracts

Rationale: Continuous EEG is a valuable tool in the assessment of poorly responsive patients with suspected seizures, a history of structural brain pathology, a history of epilepsy or events of unclear etiology. Despite the increasing availability of continuous EEG monitoring (cEEG), the role of this mode of investigation has yet to be clearly defined and more particularly the value of shorter duration routine EEG study, particularly in the Neurology ICU setting, has been questioned. We examine and compare the findings of pre-cEEG routine EEG studies to the findings of the subsequent non-elective cEEG monitoring studies. We aim to better define the role of newer longer term cEEG recording and assess the value of the more widely available routine EEG, particularly in the ICU setting.Methods: Data from 300 consecutive non-elective adult and pediatric continuous cEEG studies performed in our hospital for varying indications was examined. One hundred and eighty-nine of these studies were performed in the Intensive care Unit. Prior to 168 of the total 300 cEEG studies, a routine EEG was performed in advance of request for subsequent continuous monitoring by the supervising physician. Ninety-three of 189 cEEG studies performed in the Intensive Care Unit had a routine EEG prior to monitoring. EEG findings were classified as (i) normal, (ii) background abnormalities with out epileptiform abnormality, (iii) epileptiform abnormalities with out seizure and (iv) electrographic seizure. All studies were reviewed by a Neurophysiology/Epilepsy Fellow and a Staff Neurophysiologist. Results: Of 168 routine EEG studies, performed prior to cEEG monitoring, 28 (16.66%) were normal, 69 (41%) showed background abnormalities with out epileptiform abnormality, 34 (20.2%) showed epileptiform abnormalities with out seizure and 37 (22.02%) showed electrographic seizures. In subsequent cEEG studies, 57 (19%) were normal, 92 (30.6%) showed background abnormalities with out epileptiform abnormality, 67 (22.3%) showed epileptiform abnormalities with out seizure and 84 (28%) showed electrographic seizures. Within the group 189 patients who had cEEG monitoring performed in the ICU, in 93 cases a routine EEG was performed before cEEG study. Seven (7.5%) of these were normal, 45 (48.4%) showed background abnormalities with out epileptiform abnormality, 18 (19.3%) showed epileptiform abnormalities with out seizure and 18 (19.3%) showed electrographic seizures. Conclusions: Routine EEG showed similar findings to cEEG in all sub-groups except seizure detection. Our study shows the value of routine EEG in the assessment of the epileptiform risk, but also highlights the benefit of cEEG in event detection.