Benign Myoclonic Epilepsy in Infancy (BMEI)
Benign Myoclonic Epilepsy in Infancy (BMEI), also known as Self-Limited Epilepsy with Myoclonic Seizures, is a rare, genetically-influenced epilepsy syndrome of infancy. The ILAE classifies it as a genetic generalized epilepsy. The term “benign” is used due to its excellent prognosis for seizure control and cognitive outcome.
Presentation and Clinical Features
Age of Onset: BMEI typically begins in the first year of life, between 3 months and 3 years of age, with a peak incidence around 6-12 months.
Seizure Type: The hallmark of BMEI is the presence of myoclonic seizures. These are brief, sudden muscle jerks, often involving the head (head nods or drops) and arms (flexion or extension). The seizures are usually isolated and brief, and consciousness is not impaired.
Seizure Frequency: Myoclonic jerks can occur in clusters or be quite frequent throughout the day.
No Other Seizure Types: A key diagnostic criterion is the absence of other seizure types, such as tonic-clonic or absence seizures, at the time of diagnosis.
Neurodevelopment: Development is normal at the onset of seizures. This is a crucial feature that distinguishes it from other, more severe myoclonic encephalopathies of infancy (e.g., Dravet Syndrome).
Family History: A family history of epilepsy or febrile seizures is common.
Investigation
Diagnosis: The diagnosis is made based on the characteristic clinical presentation and the EEG findings.
EEG: The EEG is the most important diagnostic tool. It shows generalized, brief polyspike-wave discharges, which are typically enhanced by sleep and can be seen in a relaxed, awake state. Photosensitivity can also be a feature.
Differentiation: A prolonged video EEG is often necessary to distinguish BMEI from other infantile epilepsies, such as infantile spasms (West Syndrome) or Dravet Syndrome, which have very different prognoses and treatments.
Genetics: Genetic testing may be performed to rule out a pathogenic variant associated with a more severe epilepsy syndrome if the clinical picture is atypical.
Management and Prognosis
Prognosis: The prognosis for BMEI is excellent. The seizures are typically easy to control with medication and usually remit by the age of 2 to 5 years, almost always before age 8. The remission is permanent, and the children go on to have normal neurodevelopmental outcomes.
Treatment: While the syndrome is self-limited, treatment is usually indicated to control the seizures and prevent potential developmental disruption.
First-Line Medications: Levetiracetam is an excellent first-line choice due to its efficacy and favorable side-effect profile. Valproate is also highly effective but is generally avoided in young children due to potential side effects.
Other Medications: Clobazam and Benzodiazepines are also effective.
Medications to Avoid: Medications that can worsen myoclonic seizures, such as carbamazepine, should be avoided.
Discontinuation of Medication: Once the child has been seizure-free for a period of time, medication can usually be slowly tapered and discontinued with close monitoring.
ILAE Classification: The ILAE’s classification as a “self-limited” syndrome confirms that the seizures are not life-threatening and that the children have a very high chance of achieving full recovery.