Abstracts

Assessing epileptic activity in patients with continuous sharp wave during slow wave sleep (CSWS) has been difficult. Hence, the requirements for the diagnosis of CSWS have in this regard been poorly defined. This study presents a new method for an objective assessment of epileptic activity in CSWS and other diseases with large amounts of epileptic activity. Sixteen channel 24 hour ambulatory EEG recordings from patients with continuous or almost continous epileptic activity were collected. Spikes were identified by template matching on a single channel or on principal components using the Besa software. The spike/time file thus collected was used for further calculations (Matlab). The percentage of time with spiking was calculated for every time epoch in the recording and the percentage was plotted versus time. A time sequence was tagged as epileptic if the next spike appeared within the given time period (1 - 7s). The epochs were either 2 or 10 minutes. Assessment of various combinations has shown that 10-minute epochs and 1s, 3s and 5s inter spike time, plotted together, are optimal parameters. Inter-patient and intra-patient reproducibility supports the notion of a robust method. Most methods for assessing spikes have utilized histograms (number of spikes/epoch). This measure is very sensitive to spike frequency. Our method is almost independent of spike frequency and gives clinically more useful information as it quantifies spike activity and its temporal distribution through the recording. Furthermore, the method is practicable and not unacceptably time-consuming.