A case of Dravet syndrome with focal cortical myoclonus

Abstract

Background: Dravet syndrome (DS) is a severe epileptic encephalopathy in children dominated by polymorphic seizures. Focal cortical myoclonus indicated on conventional electroencephalogram (EEG) was rarely observed in DS. Case presentation: The child, boy, thirteen months old, suffered from clonic seizures during bathing at two months old. Later he suffered from recurrent afebrile or febrile generalized tonic–clonic seizures often developing into status epilepticus. A genetic analysis of the SCN1A gene revealed a de novo heterozygous frame shift mutation in exon 21(c.3836_c.3837del AT).His myoclonic jerks of unilateral arm occurred spontaneously in response to movement. A spike wave from right central-parietal cortex immediately preceded a left myoclonic muscle activity, while a spike wave from left immediately preceded a right myoclonic muscle activity. The onset of the detected spike preceded the onset of myoclonic muscle activity by 42 ms using jerk-locked back-averaging of electroencephalogram data. The focal cortical myoclonus was not noted when one year old. Conclusions: Focal cortical myoclonus could be a form of seizures during the first year of life in DS, which may broaden the types of seizures of DS and may provide some diagnostic clues for DS.