toddler with childhood myoclonic epilepsy standing on porch

What is myoclonic epilepsy of infancy?

  • Myoclonic epilepsy of infancy is a condition that occurs in previously healthy toddler-age children. There is onset of myoclonic seizures between 6 months to 2 years, although occasionally as young as 4 months and up to 5 years old.
  • Myoclonic seizures are the only seizure type at onset, although infrequent febrile seizures can occur in up to 30% of children.
  • Seizures typically resolve between 6 months and 5 years after onset.
  • There can be associated learning, motor, and behavioral difficulties, especially if seizures are not controlled.

How common is this condition?

  • This is a rare condition and accounts for less than 1% of childhood epilepsies. This is likely a slight underestimate of the true frequency and some cases may overlap with epilepsy in children with myoclonic-atonic seizures (EMAS).
  • Males are twice as likely to be affected as females.
  • There can be a family history of epilepsy or a family history of febrile seizures.

How is the diagnosis made?

  • Myoclonic epilepsy of infancy is diagnosed by key clinical and electroencephalography (EEG) features.
  • This includes normal background EEG patterns. This means that there is no diffuse background slowing or regions with focal slowing.
  • There can be evidence of an increased risk of generalized onset seizures, meaning generalized spike or polyspike-and-wave discharges, seen between seizures.
  • During myoclonic seizures there is typically an associated generalized spike or polyspike-and-wave discharge seen on the EEG that lasts 1-3 seconds.
  • Occasionally, after the myoclonic jerk, there can be loss of tone (or an atonia) associated with a drop or fall.

Seizure Types

What Testing is Needed?

  • An EEG is a key component of the diagnosis.
  • An MRI of the brain and genetic testing may be considered.

What is the cause?

A genetic cause is suggested and there are case reports of specific genetic changed identified including SLC2A1 and HCN4.

Treatment

Valproic acid is typically the anti-seizure medication of choice, although other broad-spectrum anti-seizure medications could also be considered.

Long-Term Outcomes

  • Seizures typically resolve, although for some individuals there is recurrence of seizures in adolescence.
  • These are typically generalized tonic-clonic seizures with bilateral extremity stiffening and jerking, although other types of seizures have also been reported. This occurs in 10-20% of children with a history of myoclonic epilepsy of infancy.

References

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Authored By: 
Krista Eschbach MD
Charuta Joshi MD
I
Authored Date: 
10/2020
Reviewed By: 
Elaine Wirrell MD