Abstracts

Rationale:  Diagnosis of epilepsy in the outpatient clinic depends on recording of interictal epileptiform discharges by routine EEG, as ictal recordings are rarely obtained. However, repeated routine EEG or even long-term video EEG monitoring (VEM) fails to record interictal epileptiform discharges in a subset of patients with epilepsy. Diagnosis of such patients is challenging, and their clinical features are not fully understood. The clinical features of patients with epilepsy without interictal epileptiform discharges on VEM were investigated. Methods:  A retrospective review of 626 patients, who underwent approximate 4-day VEM in our epilepsy monitoring unit from October 2011 to February 2017, identified 124 patients with epilepsy (56 men and 68 women, aged 13-76 years) showing no interictal epileptiform discharges during VEM. Clinical features of these patients including presence of seizures during VEM and MRI findings were investigated. Results: Fifty-six (45.2%) of the 124 patients had ictal recordings during VEM. Twenty-three (18.5%) of the remaining 68 patients had MRI abnormalities compatible with the semiology of their epileptic seizures, including hippocampal atrophy in 8 (34.8%), cerebral infarction in 3 (13.0%), brain tumor in 2 (8.7%), and others in 10 (43.5%). The remaining 45 patients (36.3%) had neither epileptiform EEG abnormalities nor MRI lesions, but epilepsy was diagnosed based on clinical history including seizure semiology and responsiveness to antiepileptic medication. Conclusions: VEM is very useful to capture ictal recordings for epilepsy diagnosis of patients with no interictal epileptiform discharges, in addition to MRI. However, approximately one third of epilepsy patients without interictal epileptiform discharges show neither ictal recordings during 4-day VEM nor MRI lesions. Therefore, detailed history taking is crucial for the diagnosis of those patients. Funding: None.