Severe myoclonic epilepsy of childhood

This is a malignant syndrome of childhood epilepsy.

Severe myoclonic epilepsy in infancy (SMEI) is a rare disease, characterized by febrile and afebrile, generalized and unilateral, clonic or tonic-clonic seizures that occur in the first year of life in an otherwise apparently normal infant.

Subsequent seizures may be of many types:

• complex absences
• partial clonic seizures
• myoclonic jerks
• complex partial seizures
• apnoeic attacks

Developmental delay becomes apparent within the second year of life and is followed by definite cognitive impairment and personality disorders of variable intensity.

In the borderline form, children do not present with myoclonic symptoms but have the same general picture.

SMEI is a channelopathy

• genetic studies have shown a mutation in the SCN1A gene in 70 to 80% of the patients, including the borderline forms

There are no well-established correlations between genotype and phenotype

Investigations:

• electroencephalograms, often normal at the onset, display both generalized and focal anomalies, without a specific electroencephalographic pattern
• neuroimaging is usually normal

Management (2):

• requires specialist advice - refer to, a tertiary paediatric epilepsy specialist when a child presents with suspected Dravet syndrome
• consider sodium valproate or topiramate as first-line treatment in children with Dravet syndrome. Follow the MHRA safety advice on sodium valproate
• if first-line treatments are ineffective or not tolerated, and consider clobazam or stiripentol as adjunctive treatment
• second-line treatment
  • if triple therapy is unsuccessful for Dravet syndrome and the child is aged 2 years or over, consider second-line add-on treatment options in line with NICE technology appraisal guidance on:
    • fenfluramine
    • cannabidiol with clobazam
• further treatment options
  • If triple therapy is unsuccessful for Dravet syndrome in a child aged under 2 years or second-line treatment is unsuccessful in a child aged 2 years or over, consider 1 of the following add-on options under the supervision of a ketogenic diet team or a neurologist with expertise in epilepsy, as appropriate:
    • ketogenic diet
    • levetiracetam
    • topiramate (do not use topiramate in women and girls of childbearing potential unless the conditions of the Pregnancy Prevention Programme are fulfilled)
  • if the first choice is unsuccessful, consider the other add-on options
    • in January 2025, these were off-label uses of levetiracetam and topiramate
• if all other treatment options for Dravet syndrome are unsuccessful, consider potassium bromide under the guidance of a neurologist with expertise in epilepsy
  • in January 2025, potassium bromide was not licensed for use in the UK

Be aware that the following medications may exacerbate seizures in people with Dravet syndrome:

• carbamazepine
• gabapentin
• lacosamide
• lamotrigine
• oxcarbazepine
• phenobarbital
• pregabalin
• tiagabine
• vigabatrin

Reference:

1. Dravet C. Oguni H. Dravet syndrome (severe myoclonic epilepsy in infancy).Handb Clin Neurol. 2013;111:627-33
2. NICE (August 2026). Epilepsies in children, young people and adults