Abstracts

Rationale: While seizures are classified as focal and generalized based on their onset, it is recognized that focal seizures may evolve to become generalized. The evolution of generalized onset seizures to become focal is much less recognized. This subset of seizures is important to recognize as these patients are often misdiagnosed and treated with improper anti-epileptic medications. We identified patients with this seizure type studied in our epilepsy monitoring unit from 2003-2014, and described their EEG and clinical features. Methods: The adult and pediatric Epilepsy Monitoring Unit databases at Vanderbilt Medical Center and Children's Hospital were screened to identify generalized onset seizures with focal evolution. The data collected from the medical records included age of seizure onset, seizure description and frequency, epilepsy risk factors, MRI abnormalities, neurologic examination, anti-epileptic medications before and after video EEG, and response to medications. The video EEGs were evaluated for: clinical seizure description, EEG pattern at ictal onset, evolution, and interictal epileptiform discharges. Results: Eight patients were identified, 6 males and 2 females. All of the patients developed epilepsy in childhood (ages 3-15 years). The age range for EMU evaluation was 7-56 years. The patients presented with a history of seizures suggestive of generalized tonic-clonic seizures or generalized absence seizures; however 6 of the 8 patients also had seizures with focality raising the possibility of focal seizures (such as head turning, automatisms, or unilateral arm extension). The majority of patients (7/8) were currently on two or more AEDs, having tried 1-6 other AEDs in the past. The interictal epileptiform discharges included generalized spike-and-wave discharges in all patients, but 2 also had focal discharges. Ictal discharges had a generalized onset on EEG, described as either generalized fast activity or spike-and-wave and/or polyspike-wave discharges. The focal evolution was described as rhythmic theta to alpha activity localized to either right temporal (1), left temporal (4), right frontal (2), or left frontal (1) regions. Taking into consideration all clinical and EEG data, 6 patients were classified with idiopathic generalized epilepsy (genetic) and 2 were classified with symptomatic generalized epilepsy (structural/metabolic). All of the patients had modifications to their medications following discharge (2 patients started on valproate while 1 taken off of oxcarbazepine), and 6/8 had improved seizure control, with 2 of these patients being seizure free. Conclusions: Generalized onset seizures may occasionally have focal evolution to resemble complex partial or secondarily generalized seizures, leading to a misdiagnosis of focal onset. This seizure type may occur with genetic as well as structural/metabolic forms of epilepsy. The identification of this seizure type on EEG may help clinicians choose appropriate medications, avoiding agents known to aggravate generalized onset seizures.