Myoclonic epilepsy in infancy (MEI) is a rare self-limited generalised epilepsy syndrome in which otherwise normally developing infants or young children develop brief generalised myoclonic seizures.
The syndrome was historically called benign myoclonic epilepsy in infancy, but the ILAE now prefers “self-limited” because some affected children have learning, behavioural or developmental difficulties despite eventual seizure remission.
Typical age at onset
MEI begins in infancy or early childhood, usually between about 4 months and 3 years.
Onset outside this range should prompt consideration of another epilepsy syndrome.
The defining seizure
Myoclonic seizures are brief, shock-like jerks, often involving the head and upper limbs.
The child may suddenly nod, flex the arms or drop an object. Consciousness is usually preserved or only minimally affected during a single brief jerk.
Seizure frequency
Jerks can occur singly or in short clusters and may be more noticeable when the child is drowsy or tired.
Frequency varies substantially between children.
EEG
The interictal EEG background is normal.
Myoclonic seizures are associated with generalised spike-wave or polyspike-wave discharges. Drowsiness and sleep can increase epileptiform activity.
Photosensitivity
Photosensitivity occurs in a subset of affected children.
Intermittent photic stimulation during EEG may provoke generalised discharges or myoclonic jerks.
Development
Development before seizure onset is normal.
Most children continue to develop well, but attention, learning or behavioural difficulties have been reported in some cohorts. Clear developmental regression should prompt reconsideration of the diagnosis.
What argues against MEI?
Focal seizures, epileptic spasms, tonic seizures, marked developmental impairment before seizure onset or a persistently abnormal EEG background suggest another epilepsy syndrome.
Myoclonic-atonic seizures also point toward epilepsy with myoclonic-atonic seizures rather than MEI.
MRI
MRI is not required in a classic presentation with normal development, examination and generalised EEG.
Imaging may be appropriate when there are atypical features or focal abnormalities.
Genetics
MEI is considered genetic, but most cases do not have one single identified causative gene.
A family history of febrile seizures or epilepsy may be present.
Treatment
Many children respond well to broad-spectrum antiseizure therapy.
Valproate has historically been commonly used and can be effective, but medication choice depends on the child’s age, adverse-effect profile, local practice and regional regulatory considerations.
Other medication options
Other broad-spectrum antiseizure medicines may be considered when valproate is unsuitable or ineffective.
Because controlled trials specific to MEI are limited, treatment recommendations rely heavily on syndrome experience and generalised epilepsy principles.
Medicines that can worsen myoclonus
Some medicines used primarily for focal epilepsy can aggravate myoclonic seizures.
This is another reason to distinguish MEI from focal motor seizures or movement disorders.
Prognosis
Seizures usually remit, often within childhood, which is why the syndrome is classified as self-limited.
However, a favourable seizure prognosis does not guarantee that every child will have no later learning or behavioural concerns.
Later epilepsy
A minority of children may later develop another generalised epilepsy phenotype.
Long-term follow-up should therefore focus on the whole child rather than only the disappearance of myoclonic jerks.
Worldwide diagnosis
MEI can often be diagnosed with careful clinical history and routine EEG, making it less dependent on advanced imaging or genomic testing than many severe infantile epilepsies.
Where EEG is unavailable, however, brief myoclonic movements can be difficult to distinguish from non-epileptic infant movements.
The central point
Myoclonic epilepsy in infancy is a self-limited generalised epilepsy, but “self-limited” should not be confused with “irrelevant”. Accurate identification prevents inappropriate focal-epilepsy treatment and ensures developmental concerns are not overlooked.
Related reading
Epilepsy Syndromes →
Epilepsy with Myoclonic-Atonic Seizures →
Epilepsy in Children and Young People →
Sources
- ILAE — Classification and definition of epilepsy syndromes with onset in neonates and infants
- ILAE position statement — neonatal and infant syndrome classification
Medical note: myoclonic movements in infants can be epileptic or non-epileptic. EEG correlation is often important when the diagnosis is uncertain.
Evidence checked: September 2026.