Ictal patterns EEG of a 5-month-old infant, showing electrodecremental response during an infantile spasm monitored on the last channel. Tonic sz in a child with LGS • If a tonic seizure is recorded during the EEG of a patient with LennoxGastaut syndrome, the characteristic finding is an electrodecrement or "flattening" lasting several seconds. • In addition, high-frequency rhythmic activity in the alpha-beta frequency range commonly occurs during the electrodecrement. Pearls, Perils, and Pitfalls In the Use of the Electroencephalogram Omkar N. Markand, MD, FRCPC Seminars in Neurol. 2003;23(1) • A unique EEG pattern of GPFA is seen predominantly during sleep consisting of high-frequency, 12 to 25 Hz repetitive spike discharges occurring synchronously over both hemispheres (Fig. 26).[93] It is associated most commonly with SGE (usually Lennox-Gastaut syndrome) but it may rarely occur also with PGE or in patients with focal seizures, particularly with a frontal lobe focus. This EEG pattern is usually not associated with an obvious clinical change, although subtle tonic seizures (opening of eyes and jaw, eye deviation upward) may be missed. In rare patients with PGE and 3 Hz generalized spike wave, the awake EEG may appear rather benign but the presence of GPFA during sleep is a warning that more severe encephalopathy may be present. In such patients, motor seizures are common and the disorder is likely to persist in adulthood.[94] • Generalised paroxysmal fast activity (GPFA) consists of 8–26 (most frequently around 10 Hz), 2–50 seconds (usually below 10 seconds) bursts of generalised rhythmic discharges with frontal predominance, appearing most frequently during NREM sleep. The pattern is traditionally linked to Lennox–Gastaut (LGS) or late LGS (LLGS) syndrome and associated with tonic-axial seizures, pharmacoresistency and poor prognosis including mental deterioration. Patient 2 typical 10–12 Hz GPFA episode with frontal predominance in stage 2 NREM sleep followed by slow waves. Fig. 1 Case 1: ictal polygraphic recording on a compressed time scale. EEG of seizure onset was characterized by a ... Brain, Volume 124, Issue 12, December 2001, Pages 2361–2371, https://doi.org/10.1093/brain/124.12.2361 The content of this slide may be subject to copyright: please see the slide notes for details. Fig. 1 Case 1: ictal polygraphic recording on a compressed time scale. EEG of seizure onset was characterized by a ... a slow amplitude fast activity (enlarged detail on the top of the figure) followed by a high amplitude spike and wave complex on the left derivations. This was subsequently replaced by a prolonged sharp wave discharge more evident on the left temporal area. After seizure onset there was a sudden and sustained BP fall associated with bradycardia. A plethysmogram showed a signal of increased amplitude. The respiratory rate did not show significant changes. Brain, Volume 124, Issue 12, December 2001, Pages 2361–2371, https://doi.org/10.1093/brain/124.12.2361 The content of this slide may be subject to copyright: please see the slide notes for details. Figure 7 Delta brush at seizure-onset. In this ictal intracranial EEG recording (electrographic seizure) from a ... Brain, Volume 137, Issue 1, January 2014, Pages 183–196, https://doi.org/10.1093/brain/awt299 The content of this slide may be subject to copyright: please see the slide notes for details. Intracranial electroencephalographic seizure-onset patterns: effect of underlying pathology Piero Perucca, François Dubeau, Jean Gotman Brain, Volume 137, Issue 1, January 2014, Pages 183–196, https://doi.org/10.1093/brain/awt299 • Delta brush was an uncommon pattern, exclusive to focal cortical dysplasia and occurring in <20% of focal cortical dysplasia seizures. This is an interesting finding because, to the best of our knowledge, it has not been described previously in patients with epilepsy. Before this observation, delta brush had been described in two clinical settings only, being the premiere EEG signature of the premature infant (Clancy et al., 2003) and having been recently found also in patients with anti-Nmethyl-D-aspartate receptor encephalitis (Johnson et al., 2010; Kirkpatrick et al., 2011; Schmitt et al., 2012). Mechanisms underlying the emergence of delta brush in focal cortical dysplasia are yet to be understood. Intuitively, they would be expected to differ from those involved in the other two clinical settings, as in these cases the pattern is visible on the scalp EEG. However, one of the two patients with focal cortical dysplasia with delta brush also displayed the same pattern at the onset of seizures recorded on scalp EEG (Supplementary Fig. 5). This Suppl fig 5 • Aberrant neuronal maturation is considered a prominent feature in focal cortical dysplasia (Najm et al., 2007; Guerrini and Barba, 2010), which might explain why this pathology can exhibit a pattern of activity that normally disappears with complete brain maturation.
