INTRODUCTION

Identifying seizures with prolonged duration during video-electroencephalographic (EEG) monitoring is of importance to inform clinicians when to start emergency treatment of seizures to prevent status epilepticus. The aims of this study were to assess the clinical and EEG seizure duration (SD) in consecutive patients with epilepsy who underwent prolonged video-EEG monitoring and to identify a seizure type-dependent time point to start emergency treatment based on the likelihood that seizures will not stop spontaneously. Furthermore, we sought to determine predictors of SD and explored the relationship between antiepileptic drug (AED) serum levels and SD.

MATERIAL AND METHODS

We retrospectively analyzed 1796 seizures in 200 patients undergoing video-EEG monitoring between January 2006 and March 2008.

RESULTS

Focal simple seizures lasted significantly shorter (clinical SD: 28s, EEG SD: 42 s) compared with focal complex seizures (clinical SD: 64 s, EEG SD: 62 s), and both seizure types lasted significantly shorter compared with secondarily generalized tonic-clonic seizures (GTCSs; clinical SD: 90 s, EEG SD: 96 s). There was no difference between the duration of the convulsive phase of primary GTCSs (defined as nonfocal) and that of secondarily GTCSs (each 65 s). Cumulative clinical SD (99%) was 7 min in focal complex seizures and 11 min in focal simple seizures. Mixed linear regression model demonstrated that history of status epilepticus (P = 0.034), temporal lobe seizure onset (P = 0.040), and MRI lesions (P = 0.013) were significantly associated with logarithmic EEG SD in focal epilepsies recorded with scalp electrodes. We found significant negative correlations between the AED serum level and the EEG SD in patients treated with monotherapy: carbamazepine (P < 0.001), levetiracetam (P = 0.001), oxcarbazepine (P = 0.001), and valproic acid (P = 0.038) but not with lamotrigine monotherapy and EEG SD.

DISCUSSION

Based on the results of this study, we propose 2 min of convulsive seizure activity (irrespective of focal or generalized onset) as a prolonged seizure, which could serve as a time point to consider treatment to prevent status epilepticus. In focal complex seizures, we suggest an upper limit of 7 min, and in focal simple seizures 11 min, as definition of prolonged seizures. History of status epilepticus, temporal seizure onset, and lesional MRI findings are factors associated with significantly longer SD. Negative correlations of carbamazepine, levetiracetam, oxcarbazepine, and valproic acid serum levels and SD suggest a prolonging effect on seizures during withdrawal of these AEDs during video-EEG monitoring sessions. This article is part of a Special Issue entitled "Status Epilepticus".