Abstracts

Rationale: It was previously proposed (Matsuo F. Epilepsia 46 (Suppl. 8):138, 2005) that a well-formed interictal focal epileptiform transient (IFET) in time-series display consists of abrupt departure from base (a), an upward peak (c), a trough (e) and a wave (f) (Fig: IFET template). Key characteristics include: (1) slopes b and d of peak c are smooth, (2) peak c is more-or-less symmetrical, and (3) trough e is asymmetrical. Peak-trough is followed by wave f with a wider range of variation. The study objective was to design a protocol to quantify examination of IFET waveform against a template, and test multiple scoring methods toward the goal of applying to a broader range of EEG transients and examining their ability to predict the diagnosis of epilepsy. Methods: Grids for quantification, vertical and horizontal (set independently), were applied to a template made of 5 best-formed IFET, reformatted in common average reference derivations, from the original series. Subscore1 (maximum of 20) consisted of a sum of values for a, b, c, d, and e (4 each but 2, when lacking key attribute; abruptness in a, smoothness in b and d, the nature of symmetry in c and e). Subscore2 was deflection a-c in the number of vertical grids (with c-d set at 7), Subscore3, the number of wave segments (of 10) outside f, and Subscore4, pre-base deviation (counted as the number of crossings to the next vertical grid) for the pre-base period equaling a-e. There were 3 alternative total scores: Score A = Subscore1 + Subscore2 – Subscore3 – Subscore4, Score B = Subscore1 + 2 x Subscore2 – Subscore3 – Subscore4, and Score C = Subscore1 + Subscore2 – Subscore3. The first group of 53 IFET was from the original 2004 series, including 5 best-formed IFET. The second data set was a total of 58 representative IFET, screened and reformatted in the same fashion from clinical EEG performed during 2005. Results: Mean scores are presented in Table. While 3 sets of scores are clearly separated, there was negligible difference between 2004 and 2005. Visual ranking, repeated by a single reviewer, was reproducible among IFET with extreme scores, but not for IFET ranked in the middle range. Conclusions: It was shown feasible to quantitatively examine IFET waveform and to make the scoring system internally consistent. The scope of this study was limited, because it did not formally evaluate inter-rater reproducibility. The scoring system was developed for application to waveform differentiation between IFET and variant forms of “wicket spikes” as the next step. Significant overlap between 2 groups is expected. Multiple scoring alternatives were developed to evaluate differential contribution of IFET segments: Score B emphasizes contribution of the primary peak, while Score C, negative contribution of pre-base oscillation.