Abstracts

Rationale: Severe Myoclonic Epilepsy in Infancy (Dravet Syndrome) is a severe infantile epileptic encephalopathy characterised by convulsions appearing in the first year of life often associated with fever and progressive developmental delay. Myoclonias and prolonged hemiconvulsions appear to be the most consistent seizure types in patients with Dravet Syndrome but other seizure types do occur. Aim: To study the ictal EEG and semiologic characteristics of patients with Severe Myoclonic Epilepsy in Infancy. Methods: We reviewed ictal EEG records of five patients with genetically proven Dravet Syndrome and one patient with deletion of 2q22-23 encompassing the SCN1A gene area. Correlations with seizure semiology were made by review of video recordings when available. Results: Age at time of EEG recordings ranged from 13 months to 10 years. Myoclonic seizures were captured in five patients. 44 other seizures were captured. Concomitant video recordings were available in 4 patients. 20 absence seizures were captured in two patients and induced by hyperventilation in one patient. 3 Hz Generalized spikes and waves were seen at the onset, then spikes became irregular and of lower frequency, typically lasting more than 10 seconds. On one occasion an initial absence seizure evolved into a focal discharge over the right temporal region followed by a secondarily generalized tonic clonic seizure. 11 seizures with apnoea as the primary manifestation in one patient had EEG correlates of rhythmic theta or alpha-like discharge over the right or left temporal regions. Tonic vibratory seizures were accompanied electrographically by 14-16 Hz generalized discharges more prominent posteriorly in one patient. Complex partial seizures during sleep were accompanied by rhythmic delta activity. Interictal EEG showed multifocal spikes in all patients. A predominance of posterior spikes and polyspikes discharges was seen in younger patients Conclusions: The study demonstrates the heterogeneity of seizure semiology and EEG characteristics in patients with Dravet Syndrome. An interesting pattern was the emergence of focal ictal discharge from a generalized absence seizure. This pattern has also been described in the related syndrome of GEFS+.