Epilepsy with Myoclonic-Atonic Seizures

Doose syndrome, EMAS, Epilepsy with myoclonic-astatic seizures, EMAtS, MAE, Myoclonic atonic epilepsy, Myoclonic-astatic epilepsy in early childhood

G40.4
8A61.22
10081179

Epilepsy with myoclonic-atonic seizures is a rare childhood condition that causes multiple types of seizures, especially sudden jerking movements followed by loss of muscle control. These seizures can cause children to fall suddenly, and most children also experience delays or setbacks in their development.

Table of contents

• What is epilepsy with myoclonic-atonic seizures?
• Who gets this condition?
• Types of seizures in EMAS
• Signs and symptoms
• What causes EMAS?
• How is EMAS diagnosed?
• What is the outlook?
• Related conditions

What is epilepsy with myoclonic-atonic seizures?

Epilepsy with myoclonic-atonic seizures, also known as EMAS or Doose syndrome, is a rare form of childhood epilepsy. Seizures are caused by abnormal electrical signals in the brain. In epilepsy, seizures occur repeatedly.^[1]

This condition causes about 1% to 2% of all cases of childhood epilepsy. The name comes from the most common type of seizure seen in this condition: myoclonic-atonic seizures.^[1][3]

Myoclonic-atonic seizures begin with a brief jerk (the myoclonic component), followed by a sudden loss of muscle tone (the atonic component). These seizures can cause sudden falls or more subtle head movements downward onto the chest, called head drops.^[1]

Children with EMAS mostly have generalized seizures, which are seizures that affect the whole brain. Focal seizures, which affect only one part of the brain, are rarely reported in EMAS.^[1]

Who gets this condition?

EMAS typically affects young children. The first seizure usually occurs between 2 and 6 years of age, with the peak age being 3 to 4 years. The condition can rarely begin as early as 6 months or as late as 8 years.^[1][3][4]

Boys are affected more often than girls. Studies show that males are affected 2.7 to 3.1 times more frequently than females.^[3]

Most children with EMAS have normal development before seizures begin. However, a small number of children have mild developmental delays before having their first seizure.^[1][4]

In about 1 in 4 children (20%), simple febrile seizures (seizures during fever) have occurred before the onset of EMAS.^[1][3]

Types of seizures in EMAS

EMAS can include multiple types of seizures. The first seizure is usually a generalized tonic-clonic seizure, which causes the entire body to stiffen briefly followed by rhythmic shaking. After days to months, other seizure types begin to appear.^[1][3]

Common seizure types in EMAS include:

• Myoclonic seizures: These cause brief jerking movements.
• Atonic seizures: These cause a drop due to sudden loss of muscle tone.
• Myoclonic-atonic seizures: These cause a brief jerking movement followed by a drop due to sudden loss of muscle tone.
• Tonic seizures: These cause stiffening of the whole body and can result in a fall. Brief tonic seizures may be seen in some patients.
• Tonic-clonic seizures: Also known as grand-mal seizures, these cause the entire body to stiffen briefly followed by rhythmic shaking.
• Absence seizures: Also known as petit-mal seizures, these can cause staring, unresponsiveness, or slow responses. Atypical absences occur with increasing frequency in EMAS.

Sometimes seizures can change a child’s level of consciousness without obvious signs like jerking. When this occurs and continues for a long period of time (hours to days), it is called nonconvulsive status epilepticus. During these episodes, children may show drowsiness, problems walking, and irregular muscle jerks.^[1][3]

Signs and symptoms

Main symptoms

The primary symptom of EMAS is having myoclonic-atonic seizures.^[1]

Developmental setbacks are also a key symptom. When seizures begin, a child’s development is usually normal or only mildly delayed. However, developmental setbacks begin around the same time as the seizures. Many researchers believe the seizures contribute to these setbacks, though there could be a different underlying cause for both.^[1]

Parents of children with EMAS may report:

• Regression: A loss of previously achieved milestones
• Developmental plateau: A failure to gain additional skills

The stormy phase

Most children experience an active phase when seizures become very frequent and many different seizure types occur. This intense seizure activity, along with developmental setbacks, is known as the “stormy phase.”^[1][3]

During this phase, seizures can be difficult to control with medication. Other symptoms that can appear during this period include behavior problems, sleep disorders, difficulty with planning and organizing tasks, and problems with balance and coordination.^[4]

What causes EMAS?

The exact cause of EMAS is unknown in most cases. Researchers suspect that many cases involve multiple genes working together, which is called polygenic inheritance.^[3]

Some cases are caused by changes in a single gene. The most common single-gene causes include changes in SLC6A1, CHD2, and AP2M1. Other genetic changes that have been reported include those in SLC2A1, SCN1A, SYNGAP1, KCNA2, and NEXMIF.^[3]

Most children with EMAS have had normal development before seizures start, and their birth history is usually unremarkable.^[4]

How is EMAS diagnosed?

Diagnosis of EMAS is based on several factors: medical history, the types of seizures a child has, neurological examination, and electroencephalogram (EEG) findings. An EEG is a test that measures electrical activity in the brain.^[3]

The EEG may be normal when seizures first start, or it may show a slowing of background brain activity and generalized spike-wave discharges (abnormal electrical patterns) at 2 to 3 cycles per second. Because myoclonic, atonic, and myoclonic-atonic seizures can all cause drops, a special type of EEG called video-EEG with electromyogram (EMG) of shoulder and neck muscles is essential. This test helps distinguish these seizures from other types like tonic seizures or epileptic spasms.^[3]

Brain imaging tests, such as CT or MRI scans, are typically normal in children with EMAS.^[3]

Genetic and metabolic testing should be performed if doctors suspect other conditions or when clinical features suggest a specific genetic change. A special type of EEG test using flashing lights at low frequencies should be systematically performed to rule out neuronal ceroid lipofuscinosis type 2 (CLN2 disease), which can begin at the same age.^[3]

What is the outlook?

Despite initial seizures that are difficult to control with medication, about two-thirds of children with EMAS eventually achieve epilepsy remission (freedom from seizures), usually within 3 years of when seizures first started.^[4]

The remaining patients continue to have seizures and developmental impairments. Factors that predict poorer outcomes include the presence of tonic seizures, repeated episodes of nonconvulsive status epilepticus, and slow background brain activity on EEG.^[4]

The condition has a variable outlook over time, and seizures can be challenging to control with medication, especially during the stormy phase.^[3]

Related conditions

Several other epilepsy conditions can appear similar to EMAS and must be distinguished from it:

Dravet disease differs from EMAS by having earlier onset and prolonged seizures during fever.^[3]

Myoclonic epilepsy of infancy also occurs earlier than EMAS and shows only brief myoclonic seizures as the single seizure type.^[3]

Lennox-Gastaut syndrome is frequently associated with structural or metabolic causes and has tonic seizures during sleep and atypical absences as the main seizure types.^[3]

Neuronal ceroid lipofuscinosis type 2 (CLN2 disease), with onset in the same age range, is another important condition to rule out.^[3]