Investigators at Montreal Neurological Institute and Hospital, Canada, studied intracranial electroencephalographic seizure-onset patterns associated with different epileptogenic lesions, and defined high-frequency oscillation correlates of each pattern. MRI-documented lesions included mesial temporal sclerosis, focal cortical dysplasia, periventricular nodular heterotopia, tuberous sclerosis complex, polymicrogyria, and cortical atrophy. Seizure-onset patterns (n = 7) identified across the 53 seizures sampled were as follows: low-voltage fast activity (43%); low-frequency high-amplitude periodic spikes (21%); sharp activity at -/< 13Hz (15%); spike and wave activity (9%); burst of high amplitude polyspikes (6%); burst suppression (4%); and delta brush (4%). Periodic spikes were only observed with mesial temporal sclerosis, and delta brush was exclusive to focal cortical dysplasia. Otherwise, each pattern occurred across several pathologies. Compared to other patterns, low voltage fast activity was associated with a larger seizure-onset zone (P = 0.04). Four patterns (sharp activity, low voltage fast, spike and wave, and periodic spikes) were also found in regions of seizure spread. Each of the 7 patterns was accompanied by a significant increase in high-frequency oscillations at seizure-onset. In periodic spikes and spike and wave activity, ripple and fast ripple densities continued to increase after seizure-onset. [1]

COMMENTARY. The authors conclude that (1) biologically distinct epileptogenic lesions share intracranial electroencephalographic seizure-onset patterns, suggesting that different pathological substrates can affect similarly networks or mechanisms underlying seizure generation; (2) certain pathologies are associated with EEG signatures at seizure-onset, eg. periodic spikes may reflect mechanisms specific to mesial temporal sclerosis; (3) some seizure-onset patterns (eg periodic spikes) are found in regions of spread and may not always define the epileptogenic zone; and (4) high-frequency oscillations increase at seizure-onset, independently of the pattern. Delta brush, previously described as the EEG signature of the premature infant [2], and with ANMDA encephalitis [3], the association of delta brush with epilepsy and focal cortical dysplasia appears to be a novel finding.