Abstracts

Rationale: While hypsarrhythmia is the classic EEG background pattern in patients with infantile spasms (IS), it is present in only 60% of patients at the time of diagnosis (Gaily E, et al. Dev Med Child Neurol. 2001;43:658-67). Given that remission of hypsarrhythmia is viewed as an important outcome measure, 40% of patients with IS but without hypsarrhythmia may be excluded from IS clinical trials. In addition, a recent study found that the inter-rater reliability of hypsarrhythmia is poor (Kwong G, et al. Epilepsy Currents. 2014;14:32) suggesting that remission of hypsarrhythmia may not be an optimal outcome measure. An EEG grading scale could address these short comings. Prior EEG grading scales for IS have been complex and are not in widespread use. The aim of this study was to validate a simplified EEG grading scale (referred to here as the ‘M-score') in patients with confirmed IS. The M-score is based on the premise that the burden of epileptiform discharges and the background amplitude may be the most objective and predictive measures of the IS-associated epileptic encephalopathy (referred to here as ISEE). We hypothesized that inter-rater reliability with the M-score would be better in the determination of ISEE and electrographic outcome than using current practice in the determination of hypsarrhythmia and electrographic outcome. We also hypothesized that the M-score would accurately predict electroclinical outcome. Methods: The EEGs of 19 prospectively recruited patients with confirmed electroclinical outcomes (including prolonged overnight EEG) were analyzed. The most severely epileptiform five-minute epochs from pre- and post-treatment EEGs were reviewed by three reviewers blinded to treatments and outcomes. Reviewers watched an 11-minute instructional video. The Table defines 5 possible M-scores. An M-score of 4 or 5 defines ISEE and an M-score of 3 or less defines absence of ISEE. Agreement among reviewers was assessed using the intraclass correlation (ICC). Results: When using the M-score, complete agreement on ISEE occurred with 31 of 38 (82%) epochs (ICC: 0.74 [95% CI .61-.85]) and on electrographic outcome with 15 of 19 (79%) epochs (ICC: 0.69 [95% CI .47-.86]). If at least two of the three reviewers agreed, then the prediction of electroclinical outcome was accurate in 19 of 19 post-treatment epochs when using the M-score. In contrast, when reviewers relied on current practice, complete agreement on hypsarrhythmia occurred in only 23 of 38 (61%) epochs (ICC: 0.33 [95% CI .13-.54]) confirming our hypothesis of poor inter-rater reliability in identifying hypsarrhythmia. Complete agreement on electrographic outcome occurred in only 10 of 19 [53%] epochs (ICC: 0.37 [95% CI .1-.65]) when reviewers relied on current practice. Conclusions: The inter-rater reliability was better using the M-score in determining ISEE and electrographic outcome compared to using current practice in determining hypsarrhythmia and electrographic outcome. Additionally, the M-score accurately predicted electroclinical outcomes. The M-score is a reliable and accurate EEG grading scale for the assessment of patients with IS.