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Abnormal EEG features are a hallmark of epilepsy, and abnormal frequency and network features are apparent in EEGs from people with idiopathic generalized epilepsy in both ictal and interictal states. Here, we characterize differences in the resting-state EEG of individuals with juvenile myoclonic epilepsy and assess factors influencing the heterogeneity of EEG features. We collected EEG data from 147 participants with juvenile myoclonic epilepsy through the Biology of Juvenile Myoclonic Epilepsy study. Ninety-five control EEGs were acquired from two independent studies [Chowdhury et al. (2014) and EU-AIMS Longitudinal European Autism Project]. We extracted frequency and functional network-based features from 10 to 20 s epochs of resting-state EEG, including relative power spectral density, peak alpha frequency, network topology measures and brain network ictogenicity: a computational measure of the propensity of networks to generate seizure dynamics. We tested for differences between epilepsy and control EEGs using univariate, multivariable and receiver operating curve analysis. In addition, we explored the heterogeneity of EEG features within and between cohorts by testing for associations with potentially influential factors such as age, sex, epoch length and time, as well as testing for associations with clinical phenotypes including anti-seizure medication, and seizure characteristics in the epilepsy cohort. P-values were corrected for multiple comparisons. Univariate analysis showed significant differences in power spectral density in delta (2–5 Hz) (P = 0.0007, hedges’ g = 0.55) and low-alpha (6–9 Hz) (P = 2.9 × 10−8, g = 0.80) frequency bands, peak alpha frequency (P = 0.000007, g = 0.66), functional network mean degree (P = 0.0006, g = 0.48) and brain network ictogenicity (P = 0.00006, g = 0.56) between epilepsy and controls. Since age (P = 0.009) and epoch length (P = 1.7 × 10−8) differed between the two groups and were potential confounders, we controlled for these covariates in multivariable analysis where disparities in EEG features between epilepsy and controls remained. Receiver operating curve analysis showed low-alpha power spectral density was optimal at distinguishing epilepsy from controls, with an area under the curve of 0.72. Lower average normalized clustering coefficient and shorter average normalized path length were associated with poorer seizure control in epilepsy patients. To conclude, individuals with juvenile myoclonic epilepsy have increased power of neural oscillatory activity at low-alpha frequencies, and increased brain network ictogenicity compared with controls, supporting evidence from studies in other epilepsies with considerable external validity. In addition, the impact of confounders on different frequency-based and network-based EEG features observed in this study highlights the need for careful consideration and control of these factors in future EEG research in idiopathic generalized epilepsy particularly for their use as biomarkers.

BACKGROUND: Infantile spasms constitute a severe form of epileptic encephalopathy. In the International Collaborative Infantile Spasms Study (ICISS), we showed that combining vigabatrin with hormonal therapy was more effective than hormonal therapy alone at stopping spasms between days 14 and 42 of treatment. In this planned follow-up, we aimed to assess whether combination therapy was associated with improved developmental and epilepsy outcomes at 18 months of age.METHODS: In ICISS, a multicentre, open-label, randomised controlled trial, infants were enrolled from 102 hospitals (three in Australia, 11 in Germany, two in New Zealand, three in Switzerland, and 83 in the UK). Eligible infants had a clinical diagnosis of infantile spasms and a hypsarrhythmic (or similar) electroencephalogram (EEG) no more than 7 days before enrolment. Participants were randomly assigned (1:1) by a secure website to receive hormonal therapy with vigabatrin or hormonal therapy alone. If parents consented, there was an additional randomisation (1:1) of type of hormonal therapy used (prednisolone or tetracosactide depot). Block randomisation was stratified for hormonal treatment and risk of developmental impairment. Parents and clinicians were not masked to therapy, but investigators assessing epilepsy and developmental outcomes at 18 months were masked to treatment allocation. Minimum doses were oral prednisolone 10 mg four times a day or intramuscular tetracosactide depot 0·5 mg (40 IU) on alternate days with or without oral vigabatrin 100 mg/kg per day. The primary outcome at 18 months was development as assessed by the Vineland Adaptive Behaviour Scales (VABS) composite score. Secondary outcomes were the presence or absence of epileptic seizures or infantile spasms in the previous 28 days, as recorded by parents and carers, and the use of any anti-epileptic treatment (including ketogenic diet) in the previous 28 days. Analysis was by intention to treat. The trial is registered with the ISRCTN registry, number 54363174, and EudraCT, number 2006-000788-27.FINDINGS: Between March 7, 2007, and May 22, 2014, 766 infants were screened and, of those, 377 were randomly assigned to hormonal therapy with vigabatrin (n=186) or hormonal therapy alone (n=191). 362 infants were assessed for developmental and epilepsy outcomes at 18 months, 181 in each treatment group. Mean VABS scores did not differ significantly between the combination therapy group and the hormonal therapy alone group (73·9 [SE 1·3] vs 72·7 [1·4], difference -1·2 [95% CI -4·9 to 2·6], p=0·55). Presence of epilepsy at the assessment at age 18 months was similar in both treatment groups (54 [30·0%] of 180 infants who received combination therapy vs 52 [29·2%] of 178 who received hormonal therapy alone; difference 0·8% [95% CI -8·8 to 10·4], p=0·90). Presence of spasms was also similar in both treatment groups (27 [15·0%] of 180 infants on combination therapy vs 28 [15·7%] of 178 on hormonal therapy alone; difference 0·7% [95% CI -6·9 to 8·3], p=0·85). At the 18-month assessment, 158 (44·1%) of 358 infants were on some form of anti-epileptic treatment. Initial control of spasms between days 14 and 42 of treatment was associated with higher mean VABS scores at 18 months (79·1 [SE 1·2] vs 63·2 [1·1], difference 15·9 [95% CI 12·4 to 19·5], pINTERPRETATION: Combination therapy did not result in improved developmental or epilepsy outcomes at 18 months. However, early clinical response to treatment was associated with improved developmental and epilepsy outcomes at 18 months. Longer lead-time to treatment was associated with poorer outcomes. Rapid diagnosis and effective treatment of infantile spasms could therefore improve outcomes.FUNDING: The Castang Foundation, Bath Unit for Research in Paediatrics, National Institute of Health Research, the Royal United Hospitals Bath NHS Foundation Trust, BRONNER-BENDER Stiftung/Gernsbach, University Children's Hospital Zurich.