Myoclonic-Astastic Epilepsy

A rare epilepsy syndrome of childhood characterized by the occurrence of multiple different seizure types including myoclonic-astatic, generalized tonic-clonic and absence seizures, usually in previously healthy children.

Epidemiology

The incidence is approximately 1/10,000 children. Boys are more frequently affected than girls.

Clinical description

In 94% of cases, onset occurs during the first 5 years of life, most commonly between the ages of 3-4 years. Before onset, children usually have normal psychomotor development, but primary developmental delay has been described in some. Some patients have febrile seizures prior to onset of epilepsy. Characteristic of MAE are myoclonic-atonic or myoclonic-astatic seizures, which consist of quick jerking movements (occuring axially or truncally), followed by a drop attack (loss of muscle tone), which can result in falls and injuries. Astatic seizures can also be observed without the myoclonic component. Generalized tonic-clonic seizures are also amongst the most frequently observed seizures. Absence seizures may occur. Some patients may have tonic seizures, even though some clinicians regard the occurrence of these as an exclusion criterion for MAE. Cognitive impairment is variable and both normal cognition and moderate to severe cognitive impairment have been described. Impulsivity, aggression and autistic-like behavior have been noted in some. Seizure remission occurs, on average, 3.5 years after onset but some patients may suffer from persisting intractable seizures, often along with cognitive impairment.

Etiology

Exact etiology is unknown but thought to be genetic. Several genes have been identified in patients with MAE, with and without a family history of generalized epilepsy with febrile seizures-plus (GEFS+) (see this term). These genes are SCN1A (2q24.3), SCN1B (19q13.12) and GABRG2 (5q34) but they are not usually found in sporadic patients. Up to 10% of patients with MAE have been reported to carry non-causal mutations in the SLC2A1 gene (1p34.2). Recently, some patients with MAE-like phenotypes were found to have mutations in CHD2 (15q26).

Diagnostic methods

Diagnosis is based on the occurrence of myoclonic-atonic seizures and other seizures in previously healthy children between the ages of 7 months - 6 years. Electroencephalogram (EEG) is initially normal but brief bursts of 2-5Hz spike and wave and polyspike and wave complexes are noted as the disease progresses. EEG usually shows generalized spike-wave activity interictally and during seizures and background activity can show various degrees of slowing. The presence of explanatory findings on MRI is usually thought to exclude the diagnosis of MAE.

Differential diagnosis

Differential diagnoses include Lennox-Gastaut syndrome, Dravet syndrome, Benign Myoclonic Epilepsy of Infancy (see these terms) and structural brain lesions.

Genetic counseling

In patients with identified de novo alterations and in families with a known genetic mutation associated with GEFS+, genetic counseling is possible.

Management and treatment

The primary goal of treatment is seizure control. Vaproic acid, either alone or with other antiepileptic drugs (i.e. clobazam, levetiracetam, ethosuximide or topiramate) are the primary options considered. In patients with refractory seizures, a ketogenic diet may be implemented as it has been effective in controlling seizures in some. This may be particularly relevant in patients with identified SLC2A1 mutations. Vagus nerve stimulation has also been successful in some.

Prognosis

Prognosis is variable, ranging from normal neurodevelopmental outcome and complete seizure remission after several years, to severe intellectual disability and intractable seizures. Poor prognosis may be predicted by episodes of status epilepticus and cognitive decline soon after the 1st year of onset.