Predictors of a nondiagnostic epilepsy monitoring study and yield of repeat study

ObjectiveFailure to record typical events during long-term video/EEG monitoring (LTM) leaves the diagnosis uncertain. The purpose of this study was to analyze predictors of an initial nondiagnostic LTM study and to evaluate the yield of a repeat study.MethodsWe reviewed all adult LTM studies performed at Vanderbilt University from January 2004 to June 2008. We identified 150 patients with no typical events on LTM and matched them with consecutive controls with typical events. We compared patient demographics, epilepsy risk factors, history of antiepileptic use/failures, and prior EEG and MRI results.ResultsOf 2397 LTM studies, 380 (15.8%) failed to record typical events. Absence of epilepsy risk factors and normal outpatient EEG predicted this outcome. A repeat LTM study was successful in 18 of 45 patients (42%).ConclusionThe prediction of a nondiagnostic LTM can help to reduce the cost of investigating spells of unknown nature.

Research highlights
► 15 % of initial long-term video/EEG monitoring (LTM) studies are nondiagnostic.
► Predictors of nondiagnostic LTM are normal EEGs and absence of risk factors.
► The yield of a repeat LTM study is 42%.
► Repeat LTM tend to be nondiagnostic in patients with prior normal EEGs.