WS1.3. Normal EEG: Drowsiness and Sleep, and Normal Variants

Abstract

The EEG in the normal awake child and adult is well known and needs to be known for proper reading and reporting and identifying an abnormal transient or pattern. The following are points of emphasis: Alpha rhythm seen after age of 5 years, Significant theta activity (4–7 Hz) is present in the EEG of children and adolescents. Delta activity in the awake tracing is rarely seen after the age of 5 years. Beta rhythm is seen anteriorly. All these will be discussed in details with traces. In the evaluation of abnormalities in the EEG, one needs to be constantly aware that there are many EEG transients that morphologically resemble epileptiform discharges and that need to be distinguished from diagnostically crucial epileptiform abnormalities to avoid overdiagnosis or misdiagnosis. These include: Artifacts: for example, electrode pop, muscle potentials, eye movements, electrocardiogram (EKG), chewing, electrical, etc. Normal components of ongoing background activity: for example, vertex sharp transients of sleep, f waves, slow wave sleep, POSTs, mu rhythm, lambda waves, drowsy activity during sleep in children that may often be associated with sharp components, etc. Epileptiform variants of dubious clinical significance: there are a large number of benign epileptiform variants that must be recognized, lest they be misinterpreted. Although morphologically similar, they are nonepileptogenic as they have no established relationship with the process responsible for generating epileptic seizures. Such sharp transients include 14 to 6 per second positive spikes, small sharp spikes or benign epileptiform transients of sleep, 6 Hz spike wave or phantom spike wave, wicket spikes, psychomotor variant pattern or rhythmic midtemporal discharges, breach rhythm, etc. Sleep not only activates diagnostically useful epileptiform EEG patterns, but also unmasks several types of nonepileptogenic sharp transients. It is necessary that anyone dedicating a career in epilepsy be well aware of these. Often reading EEG requires eyeballing and identifying patterns. The more the number of EEGs reviewed the more the possibility of not missing out normal patterns and rhythms. These will be demonstrated in various EEG epochs in the workshop.