Myoclonic Epilepsy in Infancy

What is myoclonic epilepsy in infancy?

Myoclonic epilepsy in 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 in 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

The typical seizures are myoclonic seizures that are described as brief sudden jerks of the extremities.
In up to one-third of patients, seizures may be triggered by various frequencies of light (photosensitivity), as well as sudden noise or touch and can more often be seen during drowsiness.
Children with photosensitivity may have seizures that are more difficult to treat.

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 in infancy.

References

Caraballo RH, Flesler S, Pasteris MC, et al. Myoclonic epilepsy in infancy: An electroclinical and long-term follow-up of 38 patients. Epilepsy; 2013. 54(9): 1605-1612.
Campostrini G, DiFrancesco JC, Castelloti B, et al. A Loss-of-Function HCN4 Mutation Associated with Familial Benign Myoclonic Epilepsy in Infancy Causes Increased Neuronal Excitability. Front Mol Neurosci. 2018; 11:269.
Epilepsydiagnosis.org

Authored By:

Charuta Joshi MD

Krista Eschbach MD

on Monday, October 19, 2020

Reviewed By:

Elaine Wirrell MD

on Friday, February 04, 2022

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