OVERVIEW

What is Severe Myoclonic Epilepsy in Infancy?

Severe Myoclonic Epilepsy in Infancy (SMEI), also known as Dravet Syndrome (DS), is an extremely rare epilepsy syndrome that begins in infancy. The condition is associated with genetic mutations and is highly challenging to treat, primarily managed through symptomatic relief, with no known cure currently available.

Due to its presentation of tonic-myoclonic seizures during episodes, it was previously referred to as Severe Myoclonic Epilepsy of Infancy (SMEI). In 1978, the disease was first described by a physician named Charlotte Dravet, and it has since been termed Dravet Syndrome.

Is Severe Myoclonic Epilepsy in Infancy Common?

It is extremely rare. Only 1 in 15,700 to 40,000 live births is affected, with no significant difference in incidence between males and females.

In 2018, Severe Myoclonic Epilepsy in Infancy was included in the First List of Rare Diseases jointly issued by China's National Health Commission and four other government departments.

SYMPTOMS

What are the main manifestations of severe myoclonic epilepsy in infants?

The main characteristic of severe myoclonic epilepsy in infants is refractory epilepsy, with children exhibiting various forms of seizures. A typical example is "tonic-clonic epilepsy," where the child's limbs become rigid and difficult to move during an episode, followed by muscle twitching accompanied by fever.

Other forms of seizures include the following:

• Generalized seizures;

• Hemilateral seizures: For example, only one arm and leg twitch while the other side remains still;

• Focal seizures: For instance, seizures limited to the head, manifesting as stereotypical "nodding" movements, which may last over 15 minutes and develop into status epilepticus.

Seizures typically appear within the first year of an infant's life, mostly between 5–8 months, and rarely as late as the second year. After onset, seizures become frequent, difficult to treat, and persist.

What other symptoms do infants with severe myoclonic epilepsy exhibit besides seizures?

• Absence seizures: Sudden episodes of impaired consciousness, unresponsiveness, returning to normal after 3–8 seconds;

• Abnormal gait: Unsteady walking, walking in a semi-squatting posture, etc.;

• Focal neurological symptoms: Such as reduced muscle tone, tremors during fine motor activities;

• Developmental delays: Including slow language development, intellectual delays, etc.;

• Behavioral disorders: Such as autism, ADHD, etc.

CAUSES

How is severe myoclonic epilepsy in infants caused?

The condition is caused by genetic mutations, primarily in the α-1 subunit of the voltage-gated sodium channel gene (SCN1A) located on chromosome 2q24. Approximately 70%–80% of cases result from SCN1A mutations, while the remaining 20%–30% are caused by mutations in other genes (such as PCDH19, SCN1B, GABRA1, etc.).

Is severe myoclonic epilepsy in infants hereditary?

It is uncertain. Most cases of severe myoclonic epilepsy in infants arise from new SCN1A mutations in the child rather than being inherited from parents. Although a small proportion of SCN1A mutations are inherited, having an SCN1A mutation does not necessarily guarantee the development of Dravet syndrome.

Is severe myoclonic epilepsy in infants contagious?

No.

DIAGNOSIS

How is severe myoclonic epilepsy in infants diagnosed?

Diagnosis is based on clinical features combined with EEG results. According to the International League Against Epilepsy criteria, the clinical features must meet the following points:

• Family history of epilepsy or febrile seizures;

• Normal development before the onset of seizures;

• First seizure occurs before 1 year of age;

• Diverse seizure types (myoclonic seizures, focal seizures, absence seizures, generalized seizures);

• EEG shows generalized spike waves and polyspike waves;

• Early focal abnormalities or photosensitivity;

• Psychomotor developmental delay after 2 years of age;

• Ataxia, pyramidal signs, or interictal myoclonus following psychomotor delay;

• Seizure worsening triggered by overheating, such as hot weather or heat therapy.

What tests are needed for severe myoclonic epilepsy in infants?

• EEG: The most important and primary test. However, it must be performed during a seizure episode; otherwise, no abnormalities may be detected. Some infants may show EEG abnormalities during interictal periods. Electrodes are placed on the infant's head to monitor neural electrical activity in the brain, aiding diagnosis based on waveform patterns.

• Imaging tests (CT, MRI, etc.): Mainly used to rule out structural brain abnormalities causing seizures.

Which conditions can severe myoclonic epilepsy in infants be confused with? How to differentiate them?

It is primarily distinguished from febrile seizures, as both conditions involve convulsions in infants and may occur with fever.

• Febrile seizures: Typically short-lasting, rarely exceeding 15 minutes or progressing to status epilepticus, and do not affect intellectual or cognitive development.

• Severe myoclonic epilepsy in infants: Seizures last longer, often exceeding 15 minutes, recur frequently, may occur without fever, and impair psychomotor and cognitive development.

TREATMENT

Which department should be consulted for severe myoclonic epilepsy in infants?

Pediatrics or Neurology.

Is hospital treatment necessary for severe myoclonic epilepsy in infants?

Yes, hospitalization is required. Severe myoclonic epilepsy in infants does not resolve on its own.

How is severe myoclonic epilepsy in infants treated?

Most infants with severe myoclonic epilepsy require two or more antiepileptic drugs to control the condition. Commonly used medications include sodium valproate, clobazam, topiramate, stiripentol, and levetiracetam.

Some reports suggest that a "ketogenic diet" (high-fat, low-carbohydrate) may also help treat severe myoclonic epilepsy in infants. This requires strong commitment from the patient and family and must be supervised by an experienced dietitian and neurologist.

Vagus nerve stimulation and deep brain stimulation surgery have also been attempted for treatment, but there is insufficient reliable data to confirm their effectiveness.

Can severe myoclonic epilepsy in infants be cured? Does it affect lifespan?

No.

Current treatments can only control seizures, but the condition persists and recurs. Most affected children do not survive to adulthood.

DIET & LIFESTYLE

What dietary precautions should infants with severe myoclonic epilepsy take?

A ketogenic diet, which consists of high-fat and low-carbohydrate ratios, can help treat severe myoclonic epilepsy in infants. However, it is crucial to follow this dietary plan under the guidance of a hospital nutrition department and avoid self-preparation.

What lifestyle precautions should infants with severe myoclonic epilepsy take?

• Reduce fever promptly when it occurs, and use antipyretics (such as acetaminophen or ibuprofen) if necessary;

• For patients sensitive to light and visual stimuli, avoid exposure to flashing lights, limit screen time, and prevent seizure triggers;

• Avoid sodium channel-blocking medications that may worsen the condition, such as carbamazepine, oxcarbazepine, lamotrigine, and phenytoin;

• Keep bathwater at a moderate temperature, avoid saunas or hot springs, and limit intense physical activity in hot weather to prevent elevated body temperature;

• Watch TV from a distance in well-lit rooms, wear sunglasses or blue-tinted lenses outdoors, and use a 100Hz screen instead of a traditional 50Hz display;

• Minimize emotional extremes and other known seizure triggers.

Do infants with severe myoclonic epilepsy require follow-up examinations?

Yes.

Seek medical attention promptly to adjust medication if seizures occur or drug resistance develops (i.e., the condition becomes difficult to control with medication).

PREVENTION

How to prevent severe myoclonic epilepsy in infants?

There is currently no effective prevention method.

For infants already diagnosed with severe myoclonic epilepsy, prompt fever reduction and avoiding flashing lights may help prevent seizures.