Electroencephalographic characteristics of Dravet syndrome

In Dravet syndrome, interictal and ictal electroencephalography (EEG) recording may remain misleading, and are not specifically altered. Moreover, there is a great polymorphism of clinical and EEG seizure types. Some can be observed in other epileptic syndromes, but others are more specific--particularly the peculiar unilateral seizures, the falsely generalized seizures, probably with a focal onset, and the unstable seizures. In some cases, the ictal manifestations are characterized by the persistent predominant recurrence of convulsive seizures, often induced by body temperature increase, eventually associated with partial complex seizures. The myoclonic events, absences with myoclonic component, obtundation status, and photosensitivity and/or pattern sensitivity are absent or appear relatively late and recur transiently for short periods. In these cases interictal EEG is characterized by the persistent paucity of paroxysmal discharges. In other cases, on a background of convulsive seizures and body temperature sensitivity, one may find a variable association of (1) myoclonic seizures of different types, (2) a strong sensitivity to light and pattern stimulations, with early onset and persistent in time. In these cases, interictal paroxysms and spontaneous and induced (intermittent photic stimulation, patterns, and eye closure) stimulation tend to appear early and to be frequent and persistent during the evolution. According to these electroclinical patterns it is possible to divide the population into two subsets, both sharing common genetic mechanisms but with a different clinical outcome.