Severe Myoclonic Epilepsy of Infancy
Myoclonic epilepsy syndromes of infancy and early childhood (ages 1 to 7)
Myoclonic seizures occur at all ages and are primary features in syndromes that affect many children. Some children experience myoclonic seizures only, but most who experience these seizures will have other seizure types as well. The childhood myoclonic epilepsies are differentiated by:
- Age when seizures begin
- Additional types of seizures
- Type of initiating seizure
- Brain-wave patterns the seizures produce
- Developmental factors
- Long-term outcome
Myoclonic seizures comprise involuntary, quick, movements that occur abruptly and with an irregular rhythm. The movements or sudden jerks can involve a single body part, a region or the whole body. The parts most often involved are the neck, arms and shoulders.
The movements can either be an extension or flexion of muscle resulting in the sudden straightening or bending of the joints involved.
Myoclonic seizures can be experienced as mild or very forceful attacks. In the more violent attacks, an object in the hands of a child might be thrown, or, if the child is standing or sitting, he might himself be thrown to the floor. The seizures may occur singly or in clusters of three or four at a time. There is no loss of consciousness with the single jerking motions , but there may be a clouding of awareness if the seizures come in rapid succession.
Myoclonic seizures often occur upon awakening or falling asleep, but can happen anytime during the day.
Myoclonic epilepsy syndromes of infancy and early childhood include:
- Neonatal myoclonic encephalopathy
- Benign myoclonic epilepsy
- Severe myoclonic epilepsy in infancy / Dravet syndrome
- Lennox-Gastaut syndrome
- Epilepsy with myoclonic-astatic seizures
Neonatal myoclonic encephalopathy (birth to 28 days)
This is a rare and devastating syndrome marked by massive myoclonic seizures involving either the whole body or the muscles on an entire side of the body. Frequently repeated jerks that have a tendency of incessantly shifting from one part of the body to another also occur. About 50 percent of newborns with this condition do not survive. The condition in most neonates who do survive evolves into Infantile Spasms or Lennox-Gastaut syndrome.
Benign myoclonic epilepsy (ages of 4 months to 3years)
Children with benign myoclonic epilepsy are otherwise normal and do not develop other types of seizures. The syndrome represents about two percent of epilepsy that develops in the first three years of life. It is more common in boys than in girls.
The myoclonic seizures are always brief and can occur at any time of the day, with an increased incidence during periods of drowsiness. The episodes almost always involve the arms and head. A few children with the condition may have seizures triggered by flashing lights.
Benign myoclonic epilepsy is associated with a family history of epilepsy or fever seizures in about 30 percent of cases. The response to treatment is excellent and any resistance to treatment does not change the long-term favorable outcome. Medications can usually be discontinued after two or three years of treatment.
Severe myoclonic epilepsy in infancy / Dravet syndrome (ages 1 to 4)
Dravet syndrome develops in infants who are normal and without neurological problems.
The disorder begins before 1 year of age, typically with rhythmic jerks (clonic seizures) triggered by fever, followed by the later development of myoclonic, atypical absence and other types of seizures. A family history of either epilepsy or febrile convulsions exists in 15 percent to 25 percent of cases.
More than 40 percent of these children are photosensitive, and may have seizures provoked by flashing lights, eye closure, or staring at certain patterns. Seizures are frequent, occurring especially upon awakening. Fever remains a strong trigger and can lead to non-stop seizures. Seizures in some of these children might even be provoked by immersion in hot bath water.
Seizures in Dravet syndrome are extremely difficult to control. The myoclonic episodes decrease and may eventually disappear. What has been normal mental development begins to deteriorate, commonly around age 2, accompanied by a lack of coordination and other neurological signs. Although the deterioration stabilizes after age 4, all of these children have some cognitive impairment, with half being severely affected.
Dravet syndrome is very rare with an incidence variously estimated between 1 in 20,000– 40,000 live births. Twice as many boys as girls develop this syndrome.
Epilepsy with myoclonic-astatic seizures / Doose syndrome (ages 1 to 5)
Astatic is defined as the inability to stand. Children with Doose syndrome have myoclonic seizures, repeated falls (atonic seizures / drop attacks) and long periods of apathy or stupor (status). Generalized tonic-clonic seizures (grand mal) may also occur, almost always at night.
These children, who are otherwise normal at the onset, may have drop attacks before, during or after experiencing myoclonic jerks. The attacks occur suddenly, without warning and without any loss of consciousness. The attacks can also be mild and manifest as a slight nodding of the head or buckling of the knees.
A hallmark of Doose syndrome is myoclonic jerks simultaneously involving both arms and shoulders accompanied with a nodding of the head. Status attacks occur in 36 percent of children with this syndrome. The episodes can last for hours or days and may involv e irregular twitching of facial muscles and limbs, drooling, and a series of drop attacks and head nodding. These episodes often begin upon awakening.
Doose syndrome is rare and accounts for only 1 percent to 2 percent of all childhood epilepsy.
There is a genetic predisposition and about 37 percent of cases have a family history of seizures. Boys are far more often affected than girls.
The outcome for some of these children is unfavorable, including possible cognitive impairment.