Myoclonic Absence Seizures in Dravet Syndrome

Dravet syndrome is a developmental and epileptic encephalopathy that occurs as a result of SCN1A mutations in more than 80% of affected individuals. The core clinical features of Dravet syndrome include febrile and afebrile seizures beginning before 12 months; multiple seizure types, usually medically refractory, including hemiclonic, generalized tonic-clonic, focal impaired awareness, myoclonic, and absence seizures; status epilepticus; and normal early development with plateau or regression by age two years. Myoclonic absence seizures have not previously been described.

This 20-year-old man had infantile-onset epilepsy with the classical clinical features of Dravet syndrome and a de novo A1326P SCN1A mutation. By five years of age, photosensitive myoclonic absence seizures had become his dominant seizure type, occurring up to 20 times per day.

The seizures were refractory to multiple antiepileptic medications and a vagus nerve stimulator.

Although photosensitivity is well recognized in Dravet syndrome, myoclonic absence seizures have not been previously reported. This rare seizure type may be underreported in Dravet syndrome, as the myoclonic features may be subtle and can be missed if thorough history taking and video recordings are not available.