Abstracts

Rationale: Despite the widespread use of EEG in clinical practice to detect interictal epileptiform discharges (IEDs) in patients with a known history of seizures, there is not a definitive understanding of how IEDs relate to clinical measures of epilepsy severity. Prior studies, for example, have not found a consistent association between the presence or frequency of IEDs and clinically reported seizure frequency, potentially because of differences in subject characteristics and EEG recording techniques. We sought to investigate this relationship in a population and setting reflective of the most common clinical usage. Methods: We analyzed the EEGs and clinical seizure records of all consenting patients with a history of at least a single focal-onset seizure who presented for routine EEG recording over one year’s time in a general academic neurophysiology laboratory (n = 198). Results: Despite adequate statistical power, we did not find an association between the presence or absence of IEDs or IED frequency and the most recently determined seizure frequency (median 2 per year). Neither IED incidence nor frequency (median 10.0 per hour) correlated with age, epilepsy duration, or antiepileptic drug use. Conclusions: Our results differ from those of some prior studies, most of which focused on more narrow subject populations, suggesting that the patient’s clinical circumstances must be taken into account before assuming the utility of IEDs on routine EEG in predicting epilepsy severity.