Abstracts

Rationale: Long-term video-EEG monitoring (LTM) is the gold standard test in the definitive diagnosis of epilepsy. However, one limitation of this test is a potential failure to capture typical events, leaving the diagnosis uncertain. We evaluated the proportion of non-diagnostic LTM studies that failed to record typical events, and investigated the value of a repeat LTM study in consecutive patients admitted to the Vanderbilt University Epilepsy Monitoring Unit (EMU) with an initial non-diagnostic study. Methods: We reviewed LTM reports for all adult patients admitted to the Vanderbilt University EMU from January 2004 to June 2008. We identified all patients who had no typical events recorded during their initial LTM study. We recorded age, gender, age at onset of spells, duration of spells since onset, presence of epilepsy risk factors, results of any prior brain imaging and prior interictal EEG results. Risk factors included developmental delay/birth injuries, febrile seizures, head trauma with loss of conscioussness greater than 5 minutes, CNS infections and family history of epilepsy. We then identified all patients who had repeat LTM studies and noted success in recording typcial spells as well as the diagnosis of recorded events (epileptic vs. nonepileptic). As a control group, we identified immediately subsequent patients who had typical spells on their first LTM study and recorded the same parameters for comparison. Results: During the study period, 380/2397 (15.8%) of all LTM studies failed to record typical events. Of the individual patients who did not have any typical events during their first time studies, 43 patients (11.3 %) were readmitted for a subsequent LTM study. The mean age was 41.1 ± 13.6 years, 26 patients were females and 17 were males. Typical events were recorded in 18 of them (42%), nine had ictal discharges and nine had non-epileptic events. The remaining 25 patients (58%) had no typical events. Brain imaging abnormalities were seen in higher percentage of patients who had ictal discharges on the subsequent LTM study (44%) than patient with non-epileptic or non-diagnotic subsequent LTM study (11% and 25 % respectively). There was no difference in number of reported risk factors between the studied and control groups or among individual groups of epileptic vs. nonepileptic events. Conclusions: Less than 20% of LTM studies fail to record typical events. Repeating an LTM study is diagnostic in about half of patients who failed to have an event on the first study and is therefore recommended, particularly in the presence of imaging abnormalities.