Abstracts

Various EEG protocols are used to evaluate children with suspected absence epilepsy. Few data are available on the length of EEG needed to reliably identify absence seizures. A standardized video-EEG protocol is being used to establish eligibility in a large, multi-center trial of CAE. The 1-hour EEG protocol includes: 5-minute waking baseline, 1^st hyperventilation (HV) trial of 3-4 minutes, photic stimulation, 2^nd HV trial, and additional wakefulness. We examined the utility of this protocol, and the duration of EEG needed to establish eligibility for this trial. Eligibility criteria include: diagnosis of CAE consistent with the ILAE classification; age 2.5 [ndash] 13 years; normal EEG background; at least one bilateral, synchronous, symmetric spike wave discharge with a frequency of 2.7 - 5 hertz and lasting at least 3 seconds. The first burst of generalized spike and wave (GSW), with or without clinical signs, lasting at least 3 seconds was considered the defining GSW burst for eligibility. To date, 55 subjects with newly diagnosed, untreated CAE have been enrolled. The standardized EEG protocol was followed in 49/55 subjects (89%). Two subjects were too young to cooperate with fixed periods of HV, two subjects had delayed HV trials, and two subjects had photic stimulation prior to HV. The EEGs of the 49 subjects who followed the recommended procotol were analyzed for this report. The first defining GSW burst occurred after a mean of 6 minutes, 43 seconds of EEG recording (range: 18 seconds to 31 minutes, 44 seconds). The first defining GSW burst occurred before or during the 1^st HV trial in 47/49 (96%), and during the 1^st 20 minutes of EEG recording in 48/49 (98%) untreated subjects. Two of 49 subjects had no GSW after the waking baseline and 1st HV trial. One subject had a defining GSW burst during the 2^nd HV trial after 31 minutes, 44 seconds of EEG recording, and one subject had a defining GSW burst during photic stimulation after 19 minutes, 6 seconds of EEG recording and then had additional GSW during a 2nd HV trial. A standardized EEG protocol in this setting is practical. To date, an awake EEG lasting 32 minutes with two HV trials would have confirmed the initial diagnosis and allowed for study inclusion in all subjects. A 20-minute awake EEG with one HV trial, as is often done in clinical practice, would have yielded false negative results in only 1/49 (2%, upper limit of 95% CI = 6%) of untreated patients. (Supported by National Institute of Neurological Disorders and Stroke.)