Effect of reducing the recording time of standard EEGs on the detection of EEG-abnormalities in the management of the epilepsies of childhood.

Purpose: The ILAE recommends baseline recordings of 30 min to detect abnormalities supporting a clinical diagnosis of epilepsy in children. A shorter recording time may be better tolerated by children and be more resource-efficient. Our aim was to determine how many abnormalities supporting a diagnosis of epilepsy would be missed by reducing the recording time of paediatric standard electroencephalograms (EEGs) from 20 to 15 min.
Methods: We evaluated standard EEGs of 300 patients aged 2 months to 17 years referred consecutively with confirmed or suspected epilepsy. EEGs were recorded for 20 min on digital media. A digital copy of each EEG was truncated to give consecutive sequences of 10 min (sequence "A") and 5 min duration (sequences "B" and "C" respectively). A panel of EEG raters blinded to the children's' details other than age identified these sequences as "normal" or "abnormal" if they contained spike waves, discrete sharp waves or notched slow waves in the respective EEG period.
Results: EEGs of 297 children were analysed (three were omitted for technical reasons). 109 out of 297 EEGs (37%) had specific abnormalities supportive of a diagnosis of an epilepsy. 17 of these EEGs showed the abnormality in EEG sequences "B" or "C" and 7 (95% CI: 1.9-12.2) out of these demonstrated the abnormality in sequence "C" only. 105 out of 297 EEGs had non-specific findings.
Conclusion: We conclude that reducing the recording time of standard EEGs to 15 min may miss abnormalities in 2.36% [95% CI: 0.63-4.09%] overall and 6.42% [95% CI: 2.2-11.8%] of those with an abnormality supportive of an epilepsy to explain the reported symptoms. This result should inform any future discussions on seeking resource-efficiencies.
(Copyright © 2012 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.)