Abstracts

Rationale: Long-term epilepsy treatment as well as presurgical evaluation often go along with a need for temporary medication withdrawal. This is commonly associated with the fear that seizures might prolong or intensify. Empiric data would be needed for a thorough risk appraisal but is as yet missing. Our study thus aimed to systematically evaluate the duration of focal onset seizures after medication cessation as a function of drug half-life. Methods: We retrospectively identified adult patients with drug resistant focal epilepsy syndromes, who underwent presurgical evaluation including stereo-EEG recording or electrocorticography (EcoG) between 01/2006 and 06/2016 (n=137). Only patients with available MRI data and video- and EEG-recorded clinical seizures were included in the study. Patients with multifocal epilepsy or unknown epileptic foci were excluded, as well as subclinical seizures, isolated auras, or status epileptic. Antiepileptic drugs (AEDs) were withdrawn upon admission and 2mg of lorazepam were only administered after a generalized seizure or four focal onset seizures in a row. The seizure duration was determined based on the EEG seizure pattern onset and cessation. In addition, the latency since start of the monitoring was noted in hours, respectively.  A negative binomial mixed model was used to compare the seizure durations before and after a cut-off, which was set at 2.5 half-lives of the individual anticonvulsive medication as this is thought to reflect the threshold between therapeutic and ineffective drug levels. Results: In total, 72 patients were included in the study and the duration of 697 seizures analyzed. On average, the patients were treated with 2.4±0.77 AEDs. The respective cut-off of 2.5 half-lives was on average 92.63±79.85 hours. A comparable amount of seizures manifested before (321/697) and after (376/697) the individual cut-off point. Similarly, the rate of secondary generalization did not change before (51/321) and after (58/376) that threshold. The mean seizure duration, though, was prolonged after 2.5 half-lives by a factor of 1.168 for focal onset seizures (p=0.090) and a factor of 1.091 for secondary generalized seizures (p=0.545). Conclusions: Although AED withdrawal increases the likelihood for epileptic seizures, it did not prolong the seizure duration, nor did it increase the rate of secondary generalization in our study. Funding: None of the authors has any conflict of interest to disclose.