Abstracts

Rationale: Angelman syndrome (AS) is a neurogenetic disorder characterized by impairment of neurologic development, poor or no language acquisition, a unique behavioral profile and a wide-based gait with jerky movements. Approximately, 90% of patients with AS have epilepsy and more than 92% of patients have characteristic rhythmic EEG abnormalities Interictal epileptiform discharges (IEDs) consisting of focal, multi-focal or generalized epileptiform discharges are also seen (Dan and Boyd, 2003). In a general epilepsy population, the mean time to the first IED has been shown to be 32.8 minutes during a prolonged outpatient EEG (Losey et al. 2008) and it has previously been shown that abbreviated EEG montages used during polysomnography (PSG) are suboptimal in seizure detection and localization ((Foldvary-Schaefer et al, 2006).The goal of this study was to define the optimal EEG recording (length and montage--full head vs. limited) needed to identify ictal, interictal and benign abnormal rhythms in AS. Methods: Overnight sleep EEGs in conjunction with overnight PSG from 16 patients with AS between the ages of 3 -16 years old enrolled in the Angelman Natural History protocol study were reviewed. A blinded electroencephalographer reviewed the first hour of each EEG using 6- and 21-channel montages. Data was first reviewed in the 6-channel montage and then in the 21-channel montage at least 72 hours later. Each EEG received a score based on finding found on the EEG. The categories scored included: overall EEG impression, EEG background appearance, presence of an occipital rhythm, rhythmic theta or delta, epileptiform abnormalities, and sleep. A second epileptologist independently reviewed the studies to confirm inter-rater reliability of the scores. After each EEG was scored in the different montages, a chart review was done to identify clinical history of seizures and any previous epilepsy monitoring unit (EMU) admissions. Results: Although 81% of patients had a clinical history of seizures and were on anti-epileptic drugs (13/16), only 18% had IED and/or ictal discharge on prolonged EEG (3/16).These proportions were similar on both the 6- and 21-lead EEGs. Only 1 of the 18 patients had an admission to the EMU. Both the limited 6-lead EEG and the full 21-lead EEG were able to distinguish benign abnormal rhythms, in particular the diffuse rhythmic delta pattern. There was 100% concordance in identifying rhythmic delta and/or theta patterns. Otherwise, the background abnormalities, presence or absence of sleep patterns, and overall background appearance were often misrepresented on the 6-lead EEG. The 6-lead EEG also missed an ictal discharge emanating from the frontal lobe. Conclusions: A limited 6-lead EEG is able to detect some common abnormal rhythms seen in AS but is sub-optimal in detecting overall background appearance and seizures in AS. In contrast to a general epilepsy population, IEDs are less likely to be detected on a prolonged EEG in AS patients, even when sleep is captured. Thus, an EMU admission may needed to characterize and localize seizures in this special population.