Electrographic seizure duration and inter‐seizure intervals in focal status epilepticus

Abstract

AbstractObjectiveTo characterize the duration of seizures and inter‐seizure intervals in focal status epilepticus (SE).MethodsWe reviewed consecutive scalp EEG recordings from adult patients who were admitted for a first episode of focal status epilepticus. We identified electrographic seizure duration and inter‐seizure intervals in the first diagnostic pretreatment EEG. We also reviewed isolated focal self‐limiting seizures in epilepsy patients, as a comparison group for seizure duration.ResultsWe recorded 307 focal seizures in 100 consecutive focal SE episodes, with a median seizure duration of 107 s (IQR: 54–186), and 134 isolated focal self‐limiting seizures in 42 epilepsy patients, with a median duration of 59 s (IQR: 30–90; p < .001). The only clinical feature of SE that significantly increased seizure duration was acute symptomatic etiology. In SE, 15% and 7% of seizures lasted longer than 300 and 600 s, respectively (t1 of the actual definition for tonic–clonic and focal SE), while only 1% of self‐limiting seizures lasted longer than 300 s, and none lasted longer than 600 s. The analysis of inter‐seizure intervals in SE with multiple seizures showed that 50% of the inter‐seizure periods were shorter than 60 s, and 95% were shorter than 540 s (9 min). Patients who had an increase in seizure duration (last versus first) of at least 1.4 times showed an increased 30‐day mortality.SignificanceFocal seizures within a SE episode showed a wide range of duration, partly overlapping with the duration of focal self‐limiting seizures but with a longer median duration. Inter‐seizure intervals within an episode of SE were shorter than 1 min in 50% of the seizures and never lasted more than 10 min. Finally, an increase in seizure duration could represent an “electrophysiological biomarker” of a more severe SE episode, which may require more aggressive and rapid treatment.